* This bug ONLY surfaces when debugging or running the program with her verbosity. To fix the bug in the code and also make Coverity happy, as suggested by derHugo in a comment, change the RemoveAll line to something like this: Thanks for contributing an answer to Stack Overflow! I'd really love to know why I'm being downvoted. Copy the n-largest files from a certain directory to the current one. It is a corner case that would flash once in the blue moon - but with serious impact on the production availability. How come an array's address is equal to its value in C? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Variant level weaknesses typically describe issues in terms of 3 to 5 of the following dimensions: behavior, property, technology, language, and resource. Why does this example of what compilers aren't allowed to do cause null pointer dereferencing using cmov? A deferred call's arguments are evaluated immediately, so the defer statement panics due to a nil response. I have the following section of code, which gives explicit null dereferenced. The description The sk pointer is initialized to tun->sk before checking if tun is a null pointer. is provided for a non-compliant code example.Thus it seems that the arrow operator (member access through pointer) is usually treated also as a dereference operation. I've changed it to say null pointer instead of invalid pointer. In this noncompliant code example, input_str is copied into dynamically allocated memory referenced by c_str. I say "theoretical" because I have not successfully produced strings of this length in testing. The issue of passing n=0 to memcpy() is distinct from null or invalid pointers. Connect and share knowledge within a single location that is structured and easy to search. Image of minimal degree representation of quasisimple group unique up to conjugacy. I've posted an example for the sake of completion-. 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. You probably don't understand that the * in a pointer declaration and the * in a pointer arithmetics expression mean completely opposite things. Created: Jan 26 2021 02:47:29 PM UTC Updated: Jan 26 2021 10:07:21 PM UTC . "Seven Pernicious Kingdoms: A Taxonomy of Software Security Errors". Aaron:I suspect we are talking past each other. This bug was quite hard to spot! This is in the key management code which converts passwords. The article easily misleads the reader into believeing that ensuring pointer validity boils down to checking for pointer being not equal to NULL. Unless explicitly stated otherwise in the description of a particular function in this subclause, pointer arguments on such a call shall still have valid values, as described in 7.1.4. This information is often useful in understanding where a weakness fits within the context of external information sources. It is pretty easy to miss such things when adding a new feature. VM {} is a viable candidate for solving affinity group violation situation. What are the advantages of running a power tool on 240 V vs 120 V? then the UB is not in your code, you just may be searching for code with potential UB. This is a matter of style, and also following code walkthrough. Passing a null pointer tomemcpy() would produce undefined behavior, even if the number of bytes to copy were 0. Example: tool developers, security researchers, pen-testers, incident response analysts. The 2nd NCCE/CS pair seems redundant with the first NCCE/CS pair. is undefined behavior (UB) if input does not actually point to a valid struct. Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. If a user supplies a malformed request or violates the client policy, the Do method can return a nil response and a non-nil err. It could cause e-mails stored with incorrect names. These types of problems usually lead to insidious correctness errors since exceptions are caught at a higher level. VM {} is NOT a viable candidate for solving affinity group violation situation. 0 is certainly within the 'domain of the function' (a phrase defined by mathematics but not by C11), as copying 0 bytes is well-understood (although silly). Should I re-do this cinched PEX connection? Is there any known 80-bit collision attack? 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! This means one of two things: In this particular case, you're explicitly setting a_ptr to the address of a variable, so it can't possibly be NULL at that point. Possible Null Pointer exception was found in a feature in which I'm the feature owner. Can this be fixed if I reassign the *var1 to NULL again. It can never evaluate to true (unless Equals has been overridden to do something screwy). Note that this code is also vulnerable to a buffer overflow (CWE-119). This compliant solution ensures that both input_str andthe pointer returned by malloc() are not null: This noncompliant code example is from a version of drivers/net/tun.c and affects Linux kernel 2.6.30 [Goodin 2009]: The sk pointer is initialized to tun->sk before checking if tun is a null pointer. For users who are mapping an issue to CWE/CAPEC IDs, i.e., finding the most appropriate CWE for a specific issue (e.g., a CVE record). This vulnerability is capable. Key here (explains table format and definitions), EXP34-C = Union( CWE-690, list) where list =. Not the answer you're looking for? I got the impression that 31 source files of Linux modules will need further adjustments. How a top-ranked engineering school reimagined CS curriculum (Ep. We've been getting report on the random crashes, and here it is, the swapped check for index and actual indexed array value. 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. with solve of this bug problems have gone. 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. C/C++ Dereference error: Dereference before null check, Solving C warning - dereferencing a null pointer. Yes the ordering matters. However there is no portable way to verify that the pointer is valid, other than checking for null. I reordered that code example to do all the checks before allocations. Search for vulnerabilities resulting from the violation of this rule on the CERT website. If copying takes place between objects that overlap, the behavior is undefined. Making statements based on opinion; back them up with references or personal experience. NULL can't point to data. "Signpost" puzzle from Tatham's collection. 2005. FWIW the pointer arithmetic is also invalid because p1 does not point to valid memory, so you scan't just say something like, That code does not violate th is rule, but it violates ARR30-C. Do not form or use out-of-bounds pointers or array subscripts. ', referring to the nuclear power plant in Ignalina, mean? These relationships are defined as ChildOf, ParentOf, MemberOf and give insight to similar items that may exist at higher and lower levels of abstraction. Find centralized, trusted content and collaborate around the technologies you use most. *var1 = 0; this dereferences the pointer, i.e. 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. Hence the error. I'd guess WG14 has considered these questions, but I haven't until now :). If the compiler finds a pointer dereference, it treats that pointer as nonnull. Copy the n-largest files from a certain directory to the current one. 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). New feature implementation got stuck for days because old code had obscure implementation which caused debuging nightmare. Right? Not the answer you're looking for? So before writing anything to some memory location memory has to allocated to the pointer. What is this brick with a round back and a stud on the side used for? Good question! The Likelihood provides information about how likely the specific consequence is expected to be seen relative to the other consequences in the list. Why does Acts not mention the deaths of Peter and Paul? 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. (I think you cover that in a different rule.) Does &((struct name *)NULL -> b) cause undefined behaviour in C11? Why did DOS-based Windows require HIMEM.SYS to boot? Off by one error: It is the third example. Parabolic, suborbital and ballistic trajectories all follow elliptic paths. <, [REF-1033] "NULL Pointer Dereference [CWE-476]". uint64_t *var1 = malloc(sizeof(uint64_t)); /* Allocate memory for one uint64_t on the heap and set var1 to point at it */. This was the kind of error that most likely would never cause a problem during development but could have wreaked havoc after a release. Find centralized, trusted content and collaborate around the technologies you use most. It is useful to have a function with portable interface but platform-dependent implementation: extern bool invalid(const void *); Improve INSERT-per-second performance of SQLite. <. 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. mruby is vulnerable to NULL Pointer. 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. It's not them. To learn more, see our tips on writing great answers. That noncompliant code example (it's currently the 3rd) came from the Linux kernel, whose source is publicly available. Ah, gotcha. The test was added to catch the possibly theoretical situation where the length of input_str was somehow the maximum size for size_t, and adding one to this size in the malloc expression (to allocated space for the trailing null byte) results in an integer overflow. 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. However, I must add a few qualifications: First of all, there is the question of whether this is for C or for C++. Adding EV Charger (100A) in secondary panel (100A) fed off main (200A), Are these quarters notes or just eighth notes? This warning thrown by Coverity if you dereference a pointer and then later on do a NULL check on it. 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. which bolsters my assertion that x->member dereferences x (or at least an offset of x). To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Base - a weakness I would also guess that pointers that point to the one-past-the-end of an array are also invalid. If your code examples are simply searching for instances of C code of this nature. The format With two string literals, "SGI_ACL_FILE" and "SGI_ACL_DEFAULT", the addition of the (unsigned char *) cast resulted in sizeof returning 7 (size of pointer minus one), rather than the length of Impacts a highly used used area of our code which could cause problems when running for extended time. cov-analyze scan is returning Reverse NULL and Customer believes Coverity is reporting false positive "Dereference before NULL check". At best ISO C is under-specified in this regard, and perhaps should explicitly say so. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. 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(). valgrind wasnt that usefull because of its slowness. Base level weaknesses typically describe issues in terms of 2 or 3 of the following dimensions: behavior, property, technology, language, and resource. It even looked as a false positive at first. Found logically dead code that would never have been accessed. Explicitly initialize all your variables and other data stores, either during declaration or just before the first usage. Allowing it to be removed. It depends on the specific details, but in general, taking the address of any valid memory is OK. The issue was fixed with Avast and AVG Antivirus version 22.11 Publish Date : 2023-04-19 Last Update Date : 2023-04-19 Collapse All Expand All Select Select&Copy Scroll To Vendor . However, the warning has value because it is pointing [sic] out that the safety of q is not trivially obvious from your function's logic. While there are no complete fixes aside from conscientious programming, the following steps will go a long way to ensure that NULL pointer dereferences do not occur. It is always true that if E is a function designator or an lvalue that is a valid operand of the unary & operator, *&E is a function designator or an lvalue equal to E. If *P is an lvalue and T is the name of an object pointer type, *(T)P is an lvalue that has a type compatible with that to which T points. Coverity is correctly telling you that, albeit in a somewhat indirect way. And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). Dereferencing a pointer that might be null " findVmViolatingPositiveAg(affinityGroup, vmToHost) " when calling " getVmsByIds . Avast and AVG Antivirus for Windows were susceptible to a NULL pointer dereference issue via RPC-interface. 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. Would you like to help any further according to different understanding and expectations for affected implementation details. Why don't we use the 7805 for car phone chargers? This error detected by CoverityScan detected a case where the driver would never run at the maximum CPI clock speed. 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. Yes -> horrible false positive No -> You removed an important piece of information. Where does the version of Hamapil that is different from the Gemara come from? Your assertion is not backed by the wording in the standard, nor by common implementer understanding. Coverity issue : Explicit Null dereferenced, How a top-ranked engineering school reimagined CS curriculum (Ep. View - a subset of CWE entries that provides a way of examining CWE content. NULL Pointer Dereference in mrb_vm_exec with super in GitHub. 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." Expressions (EXP), SEI CERT C Coding Standard - Guidelines 03. 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. One could argue that all code examples would be redundant with the first pair. but we still consider it a violation of this rule for practicality, although to be anal, it is instead a violation of ARR30-C. 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. It evaluates to true if a_ptr is not NULL. Use of the Common Weakness Enumeration (CWE) and the associated references from this website are subject to the Terms of Use. This check identifies such situation by checking all possible paths where such NULL dereferences can occur. The HandleRequest function is intended to perform a request and use a defer to close the connection whenever the function returns. This fault is buried deep within some complex logic that makes it really hard to track. This code also violates ERR33-C. Detect and handle standard library errors. LANG.MEM.NPDLANG.STRUCT.NTADLANG.STRUCT.UPD, Null pointer dereferenceNull test after dereferenceUnchecked parameter dereference, Can detect violations of this rule. I find it interesting in this case how you think in another direction. second, a de-reference of that variable. OS allows remote attackers to cause a denial of service (crash from null dereference) or execute arbitrary code via a crafted request during authentication protocol selection. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. IMHO, the rule title should be changed to something less general. Even when exception handling is being used, it can still be very difficult to return the software to a safe state of operation. (C11, S7.24.2.1). NULL pointer dereferences are frequently resultant from rarely encountered error conditions, since these are most likely to escape detection during the testing phases. This noncompliant code example is derived from a real-world example taken from a vulnerable version of the libpng library as deployed on a popular ARM-based cell phone [Jack 2007]. "Signpost" puzzle from Tatham's collection, Image of minimal degree representation of quasisimple group unique up to conjugacy. NULL pointer dereferences usually result in the failure of the process unless exception handling (on some platforms) is available and implemented. 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. 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? 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. It should be an ingrained practice. I note with interest, that ISO C does permit &*x when x is null. http://blog.llvm.org/2011/05/what-every-c-programmer-should-know_14.html. Class - a weakness that is described in a very abstract fashion, typically independent of any specific language or technology. Iflengthhas the value1, the addition yields 0, and png_malloc() subsequently returns a null pointer, which is assigned to chunkdata. Phew, we're agreed here. The expression x.Equals(null) will throw NullReferenceException if x is null. Coverity is correctly telling you that, albeit in a somewhat indirect way. Overall, I disagree with her answer, and agree with the StackOverflow response (https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be). Asking for help, clarification, or responding to other answers. Thanks for this checker. CWE, CWSS, CWRAF, and the CWE logo are trademarks of The MITRE Corporation. Would you become interested in a related clarification approach for a discussion topic like . Correct; a null pointer is not a valid pointer for the C library functions. Canadian of Polish descent travel to Poland with Canadian passport. Then we hit memcpy with length 0. The platform does add offsetof( struct_type, member) to input and dereferences that. Connect and share knowledge within a single location that is structured and easy to search. This weakness can be detected using dynamic tools and techniques that interact with the software using large test suites with many diverse inputs, such as fuzz testing (fuzzing), robustness testing, and fault injection. It looks like a logic bug, which can cause a memory leaking. * Select VMs from the broken affinity group that are running on the same host. Shouldn't the function check all pointers before dereferencing them or passing them to another function? Did the drapes in old theatres actually say "ASBESTOS" on them? Small typo nit: "such as if i t pointed to freed memory" meant to say "if it" instead (removing whitespace). So we have to check all the arguments before performing any actions. Variant - a weakness that we haven't considered here: I'd guess null pointers are not valid, even though they point to 0 bytes. Null pointer dereferences. The occurrence of this wrong index was not seen in the code. 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 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. Thus, &*E is equivalent to E (even if E is a null pointer), and &(E1[E2]) to ((E1)+(E2)). What is the symbol (which looks similar to an equals sign) called? Can I use the spell Immovable Object to create a castle which floats above the clouds? to 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. extern char _etext; . This table specifies different individual consequences associated with the weakness. This turned out to be a security flaw, now known as CVE-2015-3237. What's the rationale for null terminated strings? When c_str is dereferenced in memcpy(), the program exhibits undefined behavior. Allocated memory leaked in several cases. return p == NULL || (char *)p < &_etext; int changed to size_t and if size_t parameter's is zero, allocate one word. I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. 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 interpretation of the standard is not supported universally. Hence the error. In addition, relationships such as PeerOf and CanAlsoBe are defined to show similar weaknesses that the user may want to explore. Coverity complains below message: CID 25469 (#1 of 1): Explicit null dereferenced (FORWARD_NULL) 9. var_deref_op: Dereferencing null pointer q. I do not understand why coverity complains here. How to remove elements from a generic list while iterating over it? Will the ordering matter a bit more for the safe evaluation of involved expressions? <<< 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. This compliant solution eliminates the null pointer deference by initializing sk to tun->sk following the null pointer check. I'll add that right now, but I feel it's pointless, since it will only clutter up the question. . Whoops, you're right. This example takes an IP address from a user, verifies that it is well formed and then looks up the hostname and copies it into a buffer. Thanks for contributing an answer to Stack Overflow! <, [REF-18] Secure Software, Inc.. "The CLASP Application Security Process". I believe in this case, either expression would work. and Gary McGraw. Developer Description. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide. The sk pointer is initialized to tun->sk before checking if tun is a null pointer. Unexpected uint64 behaviour 0xFFFF'FFFF'FFFF'FFFF - 1 = 0? Generating points along line with specifying the origin of point generation in QGIS. For users who are interested in more notional aspects of a weakness. Alternate Terms Relationships 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. Thanks for contributing an answer to Stack Overflow! In 5e D&D and Grim Hollow, how does the Specter transformation affect a human PC in regards to the 'undead' characteristics and spells? . Setting an incorrect jump target leads to a certain crash if the code is exercised. The user_data pointer could be invalid in other ways, such as pointing to freed memory. <, [REF-1031] "Null pointer / Null dereferencing". Not the answer you're looking for? Pillar - a weakness that is the most abstract type of weakness and represents a theme for all class/base/variant weaknesses related to it. Find centralized, trusted content and collaborate around the technologies you use most. If you put the code above in a c file, run the analysis, does it report the warning? Buffer overflow and possibly corrupting the module database. But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Would My Planets Blue Sun Kill Earth-Life? This code also violates ERR33-C. Detect and handle standard library errors. Embedded hyperlinks in a thesis or research paper, Adding EV Charger (100A) in secondary panel (100A) fed off main (200A). Made code more compliant with other rules. Unfortunately, your link also points to code that violates this rule, and is thus undefined behavior. ssh component for Go allows clients to cause a denial of service (nil pointer dereference) against SSH servers. Which ability is most related to insanity: Wisdom, Charisma, Constitution, or Intelligence? Do not use a null in a case where an object is required, https://gcc.gnu.org/gcc-4.9/porting_to.html, ARR30-C. Do not form or use out-of-bounds pointers or array subscripts, Reconsidering pointer dereferences before null pointer checks (with SmPL), understand the source code search pattern, One of the Coccinelle software maintainers expressed opposite development views today, https://stackoverflow.com/questions/25725286/does-taking-address-of-member-variable-through-a-null-pointer-yield-undefined-be, Prior to 2018-01-12: CERT: Unspecified Relationship, Pointer Casting and Pointer Type Changes [HFC], Dereferencing an out-of-domain pointer [nullref], Section 5.2.18, "Null-Pointer Dereference", Dereferencing null pointers that were not returned by a function.
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