coverity null pointer dereference

How to force Unity Editor/TestRunner to run at full speed when in background? I suppose we can check that that is not null, but we cannot check that it is valid (in any portable way). If you are working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the if statement; and unlock when it has finished. Canadian of Polish descent travel to Poland with Canadian passport. Correct; a null pointer is not a valid pointer for the C library functions. This code also violates ERR33-C. Detect and handle standard library errors. We didn't figure ourselves where those threading issues came from and tried to hide them with hacks. Event var_deref_model: | Passing null pointer "master_uri_env" to "operator =", which dereferences it. New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. Configure coverity to check that a declared variable is initialized before usage as a pointer. The indicated severity is for this more severe case; on platforms where it is not possible to exploit a null pointer dereference to execute arbitrary code, the actual severity is low. The 4gig boundary will probably be important too with unsigned int in LP64, but since size_t will be 64-bit, there will have to be some truncation that compilers will be able to warn on. It's not them. It worked normally, but sometimes devices had cryptic types. The correct idiom is to only allocate storage if the pointer is currently NULL. I'd guess null pointers are not valid, even though they point to 0 bytes. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. Will the ordering matter a bit more for the safe evaluation of involved expressions? If you put the code above in a c file, run the analysis, does it report the warning? In particular, this paragraph enables & to cancel out * (eg &*x == x) and [] (eg &x[5] == x + 5), but not ->. How a top-ranked engineering school reimagined CS curriculum (Ep. So before writing anything to some memory location memory has to allocated to the pointer. and Gary McGraw. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. I have the following section of code, which gives explicit null dereferenced. Would such an aspect be influenced in any ways if the address of operator would be applied around similar expressions? And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. Because null pointer dereferencing is undefined behavior, the compiler (GCC in this case) can optimize away the if (!tun) check because it is performed after tun->sk is accessed, implying that tun is non-null. A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. Coverity scan helps our developers finding issues like these. Is there any known 80-bit collision attack? See C17 7.1.4p1, which says, in part: Each of the following statements applies unless explicitly stated otherwise in the detailed descriptions that follow: If an argument to a function has an invalid value (such as a value outside the domain of the function, or a pointer outside the address space of the program, or a null pointer, or a pointerto non-modifiable storage when the corresponding parameter is not const-qualified) or a type (after default argument promotion) not expected by a function with a variable number of arguments, the behavior is undefined. Why are players required to record the moves in World Championship Classical games? A non-null but invalid pointer passed to memcpy() can indeed cause undefined behavior, but that is not the issue in the noncompliant codethe pointer will either be valid or null. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). Yes the ordering matters. This fixed weird behaviour that was really hard to find. assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Horizontal and vertical centering in xltabular. Not the answer you're looking for? Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. Is it safe to publish research papers in cooperation with Russian academics? Thus I became a bit more curious about involved technical details. Shouldn't the function check all pointers before dereferencing them or passing them to another function? So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). In rare circumstances, when NULL is equivalent to the 0x0 memory address and privileged code can access it, then writing or reading memory is possible, which may lead to code execution. Which language's style guidelines should be used when writing code that is supposed to be called from another language? I'll just provide a few references to back up my beliefs. If your code examples are simply searching for instances of C code of this nature, then the UB is not in your code, you just may be searching for code with potential UB. rev2023.5.1.43405. It modifies the pointed-to data. This pointer was the resaon of a memory leak Realy nice catch by Coverity. "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. This error detected by CoverityScan detected a case where the driver would never run at the maximum CPI clock speed. rev2023.5.1.43405. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? Making statements based on opinion; back them up with references or personal experience. See the "Null pointer checks may be optimized away more aggressively" section inhttps://gcc.gnu.org/gcc-4.9/porting_to.htmlas an example with one common implementation. NULL can't point to data. This is in the key management code which converts passwords. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. I suppose there is a question of "Is a pointer that points to 0 bytes valid?" Possible Null Pointer exception was found in a feature in which I'm the feature owner. Buffer overflow difficult to find by reading the code that would result a crash if path is too long. Example: educators, technical writers, and project/program managers. Furthermore, the C++20 draft (N4860) s7.6.2.1p1 says: The unary * operator performs indirection: the expression to which it is applied shall be a pointer to an object type, or a pointer to a function type and the result is an lvalue referring to the object or function to which the expression points. ROSE does not handle cases where an allocation is assigned to an lvalue that is not a variable (such as a struct member or C++ function call returning a reference), Finds instances where a pointer is checked against NULL and then later dereferenced, Identifies functions that can return a null pointer but are not checked, Identifies code that dereferences a pointer and then checks the pointer against NULL, Can find the instances where NULL is explicitly dereferenced or a pointer is checked againstNULL but then dereferenced anyway. Now it seems that I can inform also Linux contributors with higher confidence about further change possibilities (which I detected by the means of the Coccinelle software again recently). Loading. Dereferencing a null pointer always results in undefined behavior and can cause crashes. Would you like to help any further according to different understanding and expectations for affected implementation details. On such a call, a function that locates a character finds no occurrence, a function that compares two character sequences returns zero, and a function that copies characters copies zero characters. To be precise, once length is changed to a size_t and cannot take negative values, it cannot have an invalid value. Coverity is correctly telling you that, albeit in a somewhat indirect way. The standard will simply copy 0 byteswhich is essentially a no-op. This is not a perfect solution, since 100% accuracy and coverage are not feasible. 2012-09-11. So let me be more precise in my wording: I assert that a platform whose memcpy() did anything besides copy zero bytes when given n=0 and valid src and dest pointers was not C-standards-compliant. Then we hit memcpy with length 0. It looks like a logic bug, which can cause a memory leaking. For example, run the program under low memory conditions, run with insufficient privileges or permissions, interrupt a transaction before it is completed, or disable connectivity to basic network services such as DNS. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. It would cause game actors to teleport to the wrong coordinates. very useful to find this very horrible bug in this case, we're using a pointer to memory which is not guaranteed to be zero, and potentially corrupting the malloc arena in the process. More specific than a Pillar Weakness, but more general than a Base Weakness. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed Q.931, which triggers a null dereference. In the following code, the programmer assumes that the system always has a property named "cmd" defined. Running through Coverity reports and it is having issues with the "onsSelectedCredentials.RemoveAll(x => x.Equals(null));" line here, stating "check_after_deref: Null-checking x suggests that it may be null, but it has already been dereferenced on all paths leading to the check." This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. which bolsters my assertion that x->member dereferences x (or at least an offset of x). mruby is vulnerable to NULL Pointer. You have defined pointers var1 and var2 of type uint64_t and char respectively which are pointing to NULL . Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. This compliant solution ensures that the pointer returned by png_malloc() is not null. Allocated memory leaked in several cases. Why does the second compliant example permit using possibly-null pointers? Synopsys, Inc. | Policy Statement | Contact, // Create a set of all VMs in affinity groups, // There is no need to migrate when no collision was detected. in this line you are trying to assign a value 0 to a location pointed by var1 which is NUll location ie invalid address and de-referencing a invalid /Null address will result in crash. . VM {} is NOT a viable candidate for solving affinity group violation situation. The code processes a physics modification option line given either from the command line or file. In my experience, there are reasons to check for a NULL pointer other than dereferencing it. There are other problems with this code, as is noted in the rule. May be you need to do this null check much before. The pointer could in fact be NULL and any dereference prior to that NULL check could result in a NULL pointer dereference, so you need to either do the NULL check sooner or don't deereference at that point. It even looked as a false positive at first. Found logically dead code that would never have been accessed. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. Asking for help, clarification, or responding to other answers. Relatively low, but also relatively hilarious - someone decided to "shut up" a GCC warning in 2006 by putting parentheses around an assignment used as a truth value, but misplaced Impact is low, just wanted to commend you! Yeah, I suspect once it's possible to allocate 2+gigs contiguously in amainstream install of a modern OS, we'll see a frenzy of new vulnerabilities come out. Separate it into a different function that you can call. ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. You need to show more code along with what static analysis tool you are using for us to be able to give an answer to you. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. Copy the n-largest files from a certain directory to the current one. Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. parsing /proc/self/maps under linux) one might find out whether the pointer points into mapped memory, but this is still not a guarantee of validity because it is very coarse-grained see again the above example. And in this case, there is no pointed-to data. Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. DATABASE RESOURCES PRICING ABOUT US. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). ), Does not guess that return values from malloc(), strchr(), etc., can be NULL (The return value from malloc() is NULL only if there is OOMo and the dev might not care to handle that. Why is this claimed dereferencing type-punned pointer warning compiler-specific? Aaron:I suspect we are talking past each other. accesses memory stored at its address. that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Category. Can I use the spell Immovable Object to create a castle which floats above the clouds? This bug was quite hard to spot! One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. Ah, gotcha. It would be tricky, and they would want WG14 (C working group) to at least bless this change, and more likely, make the analogous change to the C standard. It should be an ingrained practice. Could I capture, and I would be able to glean much security information from the dump? A pointer should be made to point to some valid memory location before writing something to it. Thank you for the description (comments).It Cleared my doubts. This defect on our template caused null pointer deferencing in over hundred use cases. Expressions (EXP), SEI CERT C Coding Standard - Guidelines 03. The Phase identifies a point in the life cycle at which introduction may occur, while the Note provides a typical scenario related to introduction during the given phase. Phew, we're agreed here. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. This MemberOf Relationships table shows additional CWE Categories and Views that reference this weakness as a member. That makes sense. Although not a critical application this prevents a real SQL injection. We were using the wrong "pages in" counter FreeBSD's ZFS port:could cause performance issues.Luckily this is not production code yet. Coverity's suggestion to fix this bug is to use a delete[] deallocator, but the concerned file is in C so that won't work. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. In this case, the difference is the assumption thatmalloc() always returns non-nullfor the second NCCE, whereas the first NCCE has themalloc() abstracted away. Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. I've posted an example for the sake of completion-. What's the rationale for null terminated strings? Asking for help, clarification, or responding to other answers. The purpose of that line of code is to read through the current values in the list and strip out any that have become null, there's no null check happening as far as I can tell. The two languages try to maximize compatibility, . patch id. It calls x.Equals() a "dereference", unfortunately using C/C++ terminology (for historical reasons). CWE is sponsored by the U.S. Department of Homeland Security (DHS) Cybersecurity and Infrastructure Security Agency (CISA) and managed by the Homeland Security Systems Engineering and Development Institute (HSSEDI) which is operated by The MITRE Corporation (MITRE). Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? I would never have thought of looking at this piece of code if coverity hadn't found it. Each call of the impacted function may consumes many bytes (it's a file path). This Android application has registered to handle a URL when sent an intent: The application assumes the URL will always be included in the intent. In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. In that case, if you want to change the value of the pointed-to data, well, have the pointer point to some writeable memory first! By 'valid pointers' I mean that both src and dest pointers are not null and they both point to non-overlapping arrays containing at least n bytes each. * @return a list of vms which are candidates for migration Not the answer you're looking for? Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? How to remove elements from a generic list while iterating over it? Assign an array of Swift strings to a C structure variable taking a char ** value. What does 'They're at four. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). SSL software allows remote attackers to cause a denial of service (crash) via a crafted SSL/TLS handshake that triggers a null dereference. Overview. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. NULL can't point to data. The expression x.Equals(null) will throw NullReferenceException if x is null. . you are trying to make your var1 to point to the same location as that of var2 and casting it to uint64_t.So from the above two sections var1 and var2 are pointing to NULL pointer ie nothing in simple terms. ), NPD.CHECK.CALL.MIGHTNPD.CHECK.CALL.MUSTNPD.CHECK.MIGHTNPD.CHECK.MUSTNPD.CONST.CALLNPD.CONST.DEREFNPD.FUNC.CALL.MIGHTNPD.FUNC.CALL.MUSTNPD.FUNC.MIGHTNPD.FUNC.MUSTNPD.GEN.CALL.MIGHTNPD.GEN.CALL.MUSTNPD.GEN.MIGHTNPD.GEN.MUSTRNPD.CALLRNPD.DEREF, 45 D, 123 D, 128 D, 129 D, 130 D, 131 D, 652 S, Checks for use of null pointers (rule partially covered). repository mruby/mruby prior to 3.2. It also uses the unsigned type size_t to pass the length parameter, ensuring that negative values are not passed to func(). It also permits &x[y] to translate to x + y, but that is still UB if x is null because of ARR38-C. ISO C just has no similar wording for x->member. Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. This means one of two things: The pointer could in fact be NULL and any dereference prior to that NULL check could result in a NULL pointer dereference, so you need to either do the NULL check sooner or don't deereference at that point. Making statements based on opinion; back them up with references or personal experience. :). The platform is listed along with how frequently the given weakness appears for that instance. One weakness, X, can directly create the conditions that are necessary to cause another weakness, Y, to enter a vulnerable condition. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). Thanks for contributing an answer to Stack Overflow! Allowing it to be removed. If the operand is the result of a unary * operator, neither that operator nor the & operator is evaluated and the result is as if both were omitted, except that the constraints on the operators still apply and the result is not an lvalue. I would, at the very least, put an assert(q) inside if (code2), but: Ideally you'd stick with that one if/else and put all your logic in there. Various developers and code reviewers are struggling also with evolution of the specifications for such programming languages. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. Why don't we use the 7805 for car phone chargers? The above check can't hurt, as I guess you could have a system with a 32-bit size_t that had a ton of memory and had some crazy banking/selector scheme with pointers. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. Fixed by setting name to Oh joy. To learn more, see our tips on writing great answers. Hence the error. This vulnerability is capable. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. this patch have merged in upstream master branch. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of its operand. Because null pointer dereferencing is UB, the if (!tun) check can be elided entirely by the optimizer (since the tun->sk implies that tun must be non-null). Connect and share knowledge within a single location that is structured and easy to search. For users who wish to see all available information for the CWE/CAPEC entry. The two main view structures are Slices (flat lists) and Graphs (containing relationships between entries). Are these quarters notes or just eighth notes? This was potentially problematic, due to the assert on an uninitialized variable. The choice could be made to use a language that is not susceptible to these issues. Generating points along line with specifying the origin of point generation in QGIS. FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. Network monitor allows remote attackers to cause a denial of service (crash) via a malformed RADIUS packet that triggers a null dereference. Where does the version of Hamapil that is different from the Gemara come from? valgrind wasnt that usefull because of its slowness. User without create permission can create a custom object from Managed package using Custom Rest API. Did the drapes in old theatres actually say "ASBESTOS" on them? NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Before assigning a value you need to allocate a memory and make the pointers to point to that memory location and then assign a value. Consider the following example of a typical client server exchange. I believe that dereferencing NULL should not crash the system, should not allow a write to a NULL pointer area, but should always set errno, If I am a hacker, could I trap a null failure that would force a memory dump. This one is pretty awesome. The user_data pointer could be invalid in other ways, such as pointing to freed memory. large number of packets leads to NULL dereference, packet with invalid error status value triggers NULL dereference, Chain: race condition for an argument value, possibly resulting in NULL dereference. If copying takes place between objects that overlap, the behavior is undefined. May it be expected that the address of operator will eventually be evaluated only after a pointer dereference for a desirable access to a data structure member? Is there a generic term for these trajectories? The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. However there is no portable way to verify that the pointer is valid, other than checking for null. And in this case, there is no pointed-to data. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Connect and share knowledge within a single location that is structured and easy to search. 2005-11-07. I doubt that "length" of zero is a valid parameter, and although there no copy, but we see memory allocation. In your code example, the p1my_item will be evaluated before t he & operator, and so this rule is violated, although you are really trying to do pointer arithmetic rather than see what the pointer points to. "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". It seems that my understanding needs also to grow for such information. 565), Improving the copy in the close modal and post notices - 2023 edition, New blog post from our CEO Prashanth: Community is the future of AI. Expressions (EXP), Weaknesses in the 2019 CWE Top 25 Most Dangerous Software Errors, Weaknesses in the 2021 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2020 CWE Top 25 Most Dangerous Software Weaknesses, Weaknesses in the 2022 CWE Top 25 Most Dangerous Software Weaknesses, Comprehensive Categorization: Poor Coding Practices, https://samate.nist.gov/SSATTM_Content/papers/Seven%20Pernicious%20Kingdoms%20-%20Taxonomy%20of%20Sw%20Security%20Errors%20-%20Tsipenyuk%20-%20Chess%20-%20McGraw.pdf, https://cwe.mitre.org/documents/sources/TheCLASPApplicationSecurityProcess.pdf, https://en.wikipedia.org/wiki/Null_pointer#Null_dereferencing, https://developer.apple.com/documentation/xcode/null-reference-creation-and-null-pointer-dereference, https://www.immuniweb.com/vulnerability/null-pointer-dereference.html, Cybersecurity and Infrastructure Security Agency, Homeland Security Systems Engineering and Development Institute, Null Dereference (Null Pointer Dereference), updated Applicable_Platforms, Common_Consequences, Relationships, Other_Notes, Taxonomy_Mappings, Weakness_Ordinalities, updated Common_Consequences, Demonstrative_Examples, Other_Notes, Potential_Mitigations, Weakness_Ordinalities, updated Potential_Mitigations, Relationships, updated Demonstrative_Examples, Description, Detection_Factors, Potential_Mitigations, updated Demonstrative_Examples, Observed_Examples, Relationships, updated Related_Attack_Patterns, Relationships, updated Observed_Examples, Related_Attack_Patterns, Relationships, updated Relationships, Taxonomy_Mappings, White_Box_Definitions, updated Demonstrative_Examples, Observed_Examples, updated Alternate_Terms, Applicable_Platforms, Observed_Examples, updated Demonstrative_Examples, Detection_Factors, References, Relationships. Copy the n-largest files from a certain directory to the current one. Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Copy & paste errors might not often cause system crashes, but developer headaches. I'd guess WG14 has considered these questions, but I haven't until now :). {"serverDuration": 277, "requestCorrelationId": "e2a1d936a1543fbd"}, EXP34-C. Do not dereference null pointers, Clever Attack Exploits Fully-Patched Linux Kernel, ERR33-C. Detect and handle standard library errors, one compliant and one non-compliant example, CERT Oracle Secure Coding Standard for Java, EXP01-J. Pittsburgh, PA 15213-2612 mruby is vulnerable to NULL Pointer Dereference Affected Software. I find it interesting in this case how you think in another direction. . Solutions I propose: .. View - a subset of CWE entries that provides a way of examining CWE content. Best to cite C11 s7.24.2.1 here: The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1. Monitor the software for any unexpected behavior. For users who are interested in more notional aspects of a weakness. The NULL check is unnecessary because the pointer can't be NULL, so the NULL check should be removed. Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. See "Clever Attack Exploits Fully-Patched Linux Kernel" [Goodin 2009] for an example of a code execution exploit that resulted from a null pointer dereference. Is "I didn't think it was serious" usually a good defence against "duty to rescue"?

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