coverity null pointer dereference

The two languages try to maximize compatibility, and occasionally succeed. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Copyright 20062023, The MITRE Corporation. To learn more, see our tips on writing great answers. 0->member is undefined behavior. 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! IMHO, the rule title should be changed to something less general. If your code examples are simply searching for instances of C code of this nature. In your case you are not doing it,so you have a segmentation fault(or crash) . By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. This turned out to be a security flaw, now known as CVE-2015-3237. Which language's style guidelines should be used when writing code that is supposed to be called from another language? The code processes a physics modification option line given either from the command line or file. Network monitor allows remote attackers to cause a denial of service (crash) or execute arbitrary code via malformed packets that cause a NULL pointer dereference. 412-268-5800, 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 pointer. Common logic to perform in the middle? First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. For users who are interested in more notional aspects of a weakness. can have the value zero on a call to that function. However there is no portable way to verify that the pointer is valid, other than checking for null. What should I follow, if two altimeters show different altitudes? Markus:AFAICT the respponses to this StackOverflow question agree with my previous assertions. Off by one error: It is the third example. Finally, there is the matter of the compliant solution. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); <<< CID 102061: Null pointer dereferences REVERSE_INULL <<< Null-checking " doc_bv " suggests that it may be null, but it has already been dereferenced on all paths leading to the check. The Scope identifies the application security area that is violated, while the Impact describes the negative technical impact that arises if an adversary succeeds in exploiting this weakness. Making statements based on opinion; back them up with references or personal experience. The libpng library allows applications to read, create, and manipulate PNG (Portable Network Graphics) raster image files. Identify error conditions that are not likely to occur during normal usage and trigger them. and Gary McGraw. Since the code does not check the return value from gethostbyaddr (CWE-252), a NULL pointer dereference (CWE-476) would then occur in the call to strcpy(). Believing that dereferencing NULL shouldn't crash the system doesn't make it true. :). 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. 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. This fault is buried deep within some complex logic that makes it really hard to track. What REALLY happens when you don't free after malloc before program termination? If input is null, that is technically not a null dereference, but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. I'm learning and will appreciate any help. first, a null assignment, or a comparison with null will give Coverity an evidence to believe the variable could be null. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. Finally, Clang and Coccinelle are part of the LLVM project, which will define some of the undefined behaviors in C++. *var1 = 0; this dereferences the pointer, i.e. Separate it into a different function that you can call. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. It's even called out explicitly in C17 7.24.1p2: Where an argument declared as size_t n specifies the length of the array for a function, n can have the value zero on a call to that function. Is this a false positive from Coverity or should I do something to fix this? 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. That's true. 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. What were the most popular text editors for MS-DOS in the 1980s? This does not have any impact, because it is just an assert. Otherwise, the result is a pointer to the object or function designated by its operand. NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. (In contrast, the case of passing 0 bytes to malloc is addressed in C11.) Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. So before writing anything to some memory location memory has to allocated to the pointer. Server allows remote attackers to cause a denial of service (crash) via malformed requests that trigger a null dereference. Right? http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Asking for help, clarification, or responding to other answers. 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. 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. 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. This listing shows possible areas for which the given weakness could appear. how to remove a project from coverity-scan, Remove duplicate results from multiple Coverity runs, Coverity. A Pillar is different from a Category as a Pillar is still technically a type of weakness that describes a mistake, while a Category represents a common characteristic used to group related things. Security Intelligence; Non-intrusive assessment; Developers SDK; Database . I'd really love to know why I'm being downvoted. Search for vulnerabilities resulting from the violation of this rule on the CERT website. Can this be fixed if I reassign the *var1 to NULL again ?? NULL Pointer Dereference in mrb_vm_exec with super in GitHub. Variant - a weakness At best ISO C is under-specified in this regard, and perhaps should explicitly say so. 2012-09-11. 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). It looks like a logic bug, which can cause a memory leaking. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? In the complaint version, I like to make source code checking a little quicker by putting parenthesizes around arguments to |= or &= as. The two languages try to maximize compatibility, . This check identifies such situation by checking all possible paths where such NULL dereferences can occur. This bug ONLY surfaces when debugging or running the program with her verbosity. Many modern techniques use data flow analysis to minimize the number of false positives. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. Although i'm only We haven't noticed an impact of the bug but the out of bounds access has been present since at least 2009 without anybody spotting it. This compliant solution ensures that the pointer returned by png_malloc() is not null. 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. <, [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". Do you find another previous clarification approach interesting and helpful? <. And this error has been in the codebase for the last 9 Coverty scan correctly understood the logic of this code, and reported that the loop condition is wrong. Full description here: http://curl.haxx.se/docs/adv_20150617B.html It could make a malicious server fool a client to send off data from Prototypical copy-paste error. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). That exception could have rendered the entire feature non operational (And many log messages that Unused value and previous write overwriting found in the defect meant error in algorithm. Coverity found a case where a copy/paste action went wrong. Likewise, pointers to freed memory are not valid. Description. Null pointer dereferences. Developer Description. Copy & paste errors might not often cause system crashes, but developer headaches. Identify all variables and data stores that receive information from external sources, and apply input validation to make sure that they are only initialized to expected values. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. What is it that I did not understand? If you put the code above in a c file, run the analysis, does it report the warning? The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. Improve INSERT-per-second performance of SQLite. I suppose there is a question of "Is a pointer that points to 0 bytes valid?" Even documented "we don't need to care, I think" issue can become an issue when one does not check the background implementation. that is still mostly independent of a resource or technology, but with sufficient details to provide specific methods for detection and prevention. How to force Unity Editor/TestRunner to run at full speed when in background? 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. 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). Will the ordering matter a bit more for the safe evaluation of involved expressions? It does not give the pointer a new value. This rule applies to all null pointers, regardless of which function returned them. is undefined behavior (UB) if input does not actually point to a valid struct. Customer's opinion is that it is always a good practice to check a pointer for a NULL Value before freeing it. EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. Coverity is correctly telling you that, albeit in a somewhat indirect way. A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit. Only irrelevant information has been removed. 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. Find centralized, trusted content and collaborate around the technologies you use most. If you don't set it again before the above if statement, that means that the NULL check is unnecessary and should be removed. In this scenario, by the time, I come in 'cond2', I already have 'q' set. Wikipedia. patch id. In some situations, however, dereferencing a null pointer can lead to the execution of arbitrary code [Jack 2007,van Sprundel 2006]. 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. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. 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. Yes the ordering matters. FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. valgrind wasnt that usefull because of its slowness. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. What is the symbol (which looks similar to an equals sign) called? That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Thank you for clarifying your assertion until I understood it properly. It does not give the pointer a new value. Thanks, David! 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. It seems that my understanding needs also to grow for such information. This is a matter of style, and also following code walkthrough. SIZE_MAX is the largest possible value that a size_t could take, so it is not possible to have anything larger than SIZE_MAX. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If code1 and code2 may both be true, though, then you do have a substantial bug here. 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. Pittsburgh, PA 15213-2612 This error detected by CoverityScan detected a case where the driver would never run at the maximum CPI clock speed.

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