coverity null pointer dereference

NULL can't point to data. In the first compliant example it's useless to do allocation if the essential pointer user_data is NULL. If you put the code above in a c file, run the analysis, does it report the warning? http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Can this be fixed if I reassign the *var1 to NULL again. Can I use an 11 watt LED bulb in a lamp rated for 8.6 watts maximum? is undefined behavior (UB) if input does not actually point to a valid struct. Finding the distance from a corner of a cube to the midpoint of an edge. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Suppressing a null dereference warning in static analysis coming from stub implementations in tests, Visual Studios giving me Dereferencing Null Pointer warning. The platform is listed along with how frequently the given weakness appears for that instance. 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. If code1 and code2 may both be true, though, then you do have a substantial bug here. Configure coverity to check that a declared variable is initialized before usage as a pointer. ), 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. I would also guess that pointers that point to the one-past-the-end of an array are also invalid. 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. Assign an array of Swift strings to a C structure variable taking a char ** value. ), [REF-6] Katrina Tsipenyuk, Brian Chess Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. @HemantBhargava - you may know that, but the code you have shown us does not ensure that. This rule applies to all null pointers, regardless of which function returned them. This was the kind of error that most likely would never cause a problem during development but could have wreaked havoc after a release. Making statements based on opinion; back them up with references or personal experience. Good question! When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. 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). . * @return a list of vms which are candidates for migration Note that it doesn't know how to check for non-heap, non-stack. To learn more, see our tips on writing great answers. In the case of the ARM and XScale architectures, the 0x0 address is mapped in memory and serves as the exception vector table; consequently, dereferencing 0x0 did not cause an abnormal program termination. I suppose we can check that that is not null, but we cannot check that it is valid (in any portable way). The choice could be made to use a language that is not susceptible to these issues. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. I've changed it to say null pointer instead of invalid pointer. Synopsys, Inc. | Policy Statement | Contact. Thanks, David! Coverity Scan - Static Analysis Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc. The expression x.Equals(null) will throw NullReferenceException if x is null. By clicking Post Your Answer, you agree to our terms of service, privacy policy and cookie policy. For users who want to customize what details are displayed. Without coverity i probably would not have found this copy&paste error. It does not give the pointer a new value. rev2023.5.1.43405. mruby is vulnerable to NULL Pointer Dereference Affected Software. Shouldn't the function check all pointers before dereferencing them or passing them to another function? 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. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. * @param vmToHost vm to host assignments How to force Unity Editor/TestRunner to run at full speed when in background? If copying takes place between objects that overlap, the behavior is undefined. Improve INSERT-per-second performance of SQLite. If the compiler finds a pointer dereference, it treats that pointer as nonnull. <, [REF-1031] "Null pointer / Null dereferencing". FORWARD_NULL: A program will normally crash when a NULL pointer is dereferenced. See C23 (n3096) s6.5.3.2p3: The unary & operator yields the address of 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. Your assertion is not backed by the wording in the standard, nor by common implementer understanding. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Apple. This vulnerability is capable. 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). Only irrelevant information has been removed. This has been there for decade, and was shipped in a real product. Unexpected behavior can be pain to hunt down when one of these is involved. Wikipedia. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? Created: Jan 26 2021 02:47:29 PM UTC Updated: Jan 26 2021 10:07:21 PM UTC . 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. 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(). 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. Content Discovery initiative April 13 update: Related questions using a Review our technical responses for the 2023 Developer Survey, Coverity - Explicit null dereferenced (FORWARD_NULL) in contentResolver.delete(), Coverity report meanings - PW.INCLUDE_RECURSION, Extracting coverity .csv file from coverity server, C# Coverity giving "Dereference before null check (REVERSE_INULL)" on a RemoveAll call to remove null entries from a list. rev2023.5.1.43405. Possibly Clang/LLVM may choose to always return a valid value for &NULL->member. Optimizers are optimizing based on this latitude and have been for years. 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. He also rips off an arm to use as a sword, Canadian of Polish descent travel to Poland with Canadian passport, assertions usually only apply at debug-time (as I was recently reminded with a runtime crash in a release build that made no sense after all, I have assertion safety everywhere, right?). Should I re-do this cinched PEX connection? Pointer members in structs are not checked. can have the value zero on a call to that function. If you want to change the value of your pointer, just do. Copy the n-largest files from a certain directory to the current one. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. Making statements based on opinion; back them up with references or personal experience. 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. Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. VM {} is NOT a viable candidate for solving affinity group violation situation. valgrind wasnt that usefull because of its slowness. It modifies the pointed-to data. . of making the mruby interpreter crash, thus affecting the. CVE-2023-1587 : Avast and AVG Antivirus for Windows were susceptible to IMHO, the rule title should be changed to something less general. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. The software's operation may slow down, but it should not become unstable, crash, or generate incorrect results. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. 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). What REALLY happens when you don't free after malloc before program termination? 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. Possible Null Pointer exception was found in a feature in which I'm the feature owner. Could I capture, and I would be able to glean much security information from the dump? NULL Pointer Dereference in mruby/mruby- vulnerability database First if executes for cond1 and else executes for cond2.. Only one of them could be true at a time. Class level weaknesses typically describe issues in terms of 1 or 2 of the following dimensions: behavior, property, and resource. If an attacker can control the program's environment so that "cmd" is not defined, the program throws a NULL pointer exception when it attempts to call the trim() method. 33615. It also adds assertions to document that certain other pointers must not be null. However there is no portable way to verify that the pointer is valid, other than checking for null. I doubt that "length" of zero is a valid parameter, and although there no copy, but we see memory allocation. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. Fixed by setting name to Oh joy. What is this brick with a round back and a stud on the side used for? Possible Null Pointer exception was found in a feature in which I'm the feature owner. Thanks! Clearly the standard enumerates 1 case of undefined behavior, but makes no special mention of n=0. Otherwise, the result is a pointer to the object or function designated by its operand. If an invalid value has been assigned to the pointer, the behavior of the unary * operator is undefined.115). 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. 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. The code is dead and will be never processed because 'decoded' outside the scope and redefined in local. At best ISO C is under-specified in this regard, and perhaps should explicitly say so. Negative index used in the code could result in a totally wrong behavior in the application. then the UB is not in your code, you just may be searching for code with potential UB. Thank you for clarifying your assertion until I understood it properly. 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. 2005. 2019-07-15. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); *var1 = 0; this dereferences the pointer, i.e. Right? COVERITY checker description | The STAR experiment 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. Coverity Prevent cannot discover all violations of this rule, so further verification is necessary, Detects when NULL is dereferenced (Array of pointers is not checked. Can I use the spell Immovable Object to create a castle which floats above the clouds? This code also violates ERR33-C. Detect and handle standard library errors. Copyright 20062023, The MITRE Corporation. That exception could have rendered the entire feature non operational (And many log messages that the user wouldn't understand). Why does the narrative change back and forth between "Isabella" and "Mrs. John Knightley" to refer to Emma's sister? Either the check against null is unnecessary, or there may be a null pointer dereference. In the complaint version, I like to make source code checking a little quicker by putting parenthesizes around arguments to |= or &= as. More specific than a Pillar Weakness, but more general than a Base Weakness. I guess you could write a proposal to modify the C Standard, but our coding standard is meant to provide guidance for the existing language. What is it that I did not understand? it may still not be enough to satisfy Coverity. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. Category. 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. It's not them. Check the results of all functions that return a value and verify that the value is non-null before acting upon it. Does &((struct name *)NULL -> b) cause undefined behaviour in C11? assert(!invalid(p)); // or whatever, bool invalid(const void *p) { Coverity complains below message: I do not understand why coverity complains here. Horizontal and vertical centering in xltabular. This was potentially problematic, due to the assert on an uninitialized variable. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. Right? * @param affinityGroup broken affinity rule For users who wish to see all available information for the CWE/CAPEC entry. Standing by. The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. 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. One situation this can happen is when the pointer has been checked against NULL and is dereferenced later. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. If you trigger an unhandled exception or similar error that was discovered and handled by the application's environment, it may still indicate unexpected conditions that were not handled by the application itself. Thanks for contributing an answer to Stack Overflow! 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. Asking for help, clarification, or responding to other answers. Coverity is correctly telling you that, albeit in a somewhat indirect way. It worked normally, but sometimes devices had cryptic types. And Coverity will tend to interpret your code rather than reading your mind. But no where in that particular idiom would a NULL pointer necessarily be deferenced. Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). Buffer overflow difficult to find by reading the code that would result a crash if path is too long. This HandleRequest Function evaluates the close before checking the error. Null pointer dereferences. Unfortunately the problem is much more complex, and generally unsolvable within standard C. Consider the following example: There's no way f can check whether x points into valid memory or not. This fault is buried deep within some complex logic that makes it really hard to track. Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. Is there any known 80-bit collision attack? The idea is not to guarantee validity, but to catch a substantial number of problems that could occur. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, Asside - I would suggest initialising your pointers to, It's impossible to tell from that code whether. 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. accesses memory stored at its address. 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. 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. This code also violates ERR33-C. Detect and handle standard library errors. It is kind of funny, though. In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? Extended Description NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. As a result, this noncompliant code example is vulnerable to a null pointer dereference exploit, because null pointer dereferencing can be permitted on several platforms, for example, by using mmap(2) with the MAP_FIXED flag on Linux and Mac OS X, or by using the shmat() POSIX function with the SHM_RND flag [Liu 2009]. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. That interpretation of the standard is not supported universally. In particular, ROSE ensures that any pointer returned by malloc(), calloc(), or realloc() is first checked for NULL before being used (otherwise, it is free()-ed). ", Getting warning - Dereferencing before possibly being null in C code, How a top-ranked engineering school reimagined CS curriculum (Ep. uint64_t *var1 = NULL; this declares a uint64_t pointer (type uint64_t*). Asking for help, clarification, or responding to other answers. This turned out to be a security flaw, now known as CVE-2015-3237. View Defect : ScummVM: OVERRUN: C/C++: Memory - illegal accesses: Realy nice catch by Coverity. What is it that I did not understand? And in this case, there is no pointed-to data. NULL pointer dereference issues can occur through a number of flaws, including race conditions, and simple programming omissions. Can corresponding author withdraw a paper after it has accepted without permission/acceptance of first author. This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. The code processes a physics modification option line given either from the command line or file. Asking for help, clarification, or responding to other answers. If malloc() fails, it returns a null pointer that is assigned to c_str. At this point we define size as strlen(input_str) + 1. Variable "var" was uninitialized, then function that was supposed to fill it in was called. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. Not the answer you're looking for? Chat client allows remote attackers to cause a denial of service (crash) via a passive DCC request with an invalid ID number, which causes a null dereference. How NULL access (FORWARD_NULL) is reported in Coverity - Synopsys

Lawrenceville Drug Bust, Articles C