null pointers should not be dereferenced null pointers should not be dereferenced

This sounds indeed like a bug in the flow when an exception is raised. How to tell which packages are held back due to phased updates. Hi @Michael! Thered be huge value in jumping onto the latest version of the ecosystem (notably SonarQube), and benefit from all latest analyzers (e.g. This is a matter of style, and also following code walkthrough. public boolean isNameEmpty() { return getName().length() == 0; // Noncompliant; the result of getName() could be null, but isn't null-checked } . rev2023.3.3.43278. Browse other questions tagged, Where developers & technologists share private knowledge with coworkers, Reach developers & technologists worldwide, It is a false positive, but it might be a good idea not to do the, Sonar false-positive on rule: Null pointers should not be dereferenced, How Intuit democratizes AI development across teams through reusability. In the meantime, Im locking this thread. It does not point to any area of memory. The standard will simply copy 0 byteswhich is essentially a no-op. 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. Your assertion is not backed by the wording in the standard, nor by common implementer understanding. Does Counterspell prevent from any further spells being cast on a given turn? {"serverDuration": 214, "requestCorrelationId": "084acdc104f21c51"}, 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. A common memory-leak idiom, is reallocating storage and assigning its address to a pointer that already points to allocated storage. (In contrast, the case of passing 0 bytes to malloc is addressed in C11.) This rule applies to all null pointers, regardless of which function returned them. Asking for help, clarification, or responding to other answers. Even if the object is null in this case, it will not give an exception and will print ' null ' to the output stream. sometimes FP occurs. Possible fix: Assign a valid address to the pointer in all branches of the conditional statement.. Pointer can point to dynamically allocated memory. This issues is displayed by SonarQube. This is indeed an obvious False Positive from the rule. Isn't easier just to check valid range of length? [4] Find centralized, trusted content and collaborate around the technologies you use most. uninitialized reference-type class members. That is only true if possibleNumbers contains no element.. BTW: none of these warnings are shown by . With their flexibility, void pointers also bring some constraints. can have the value zero on a call to that function. So we have to check all the arguments before performing any actions. It also reinforces the notion to the reader that any time you see arithmetic in an allocation expression, you need to think about corner-cases. void *pointerVariableName = NULL; Since they are very general in nature, they are also known as generic pointers. False-positives are pointed out in other SO posts (1 & 2), where nulls are involved across functions and procedures. The return value from strchr() is often NULL, but the dev might know that a specific strchr() function call will not return NULL. So you can declare a string t and then add characters to the string with a plus sign : t += 'a'; The code you are having issue with is just moving the pointer to the next character which the foreach is already doing. Things go fine now. Optimizers are optimizing based on this latitude and have been for years. Here is our source code: Sign in to download full-size image 5.2 Part 2 Sometimes a helper function is de ned to perform the memory allocation. 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. While the engine is in practice already able to explore code from other files if needed (relying solely on bytecode), we restrain this approach to a limited set of well-known methods from standard libraries, for which we know that behaviors are correctly produced. The final NCCE is actually more insidious than it seems at first. 4. We have a false positive with the " Null pointers should not be dereferenced -squid:S2259" rule : We have a "NullPointerException" false positive for which we do not know how to solve it. What methods/tools can be used to determine the cause so that you stop the exception from causing the progra. Likewise, pointers to freed memory are not valid. The null concept refers to the idea that a pointer can hold a special value that is not equal to another pointer. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Appropriate typecasting is necessary. 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. NULL vs Void Pointer - Null pointer is a value, while void pointer is a type. The problem is that something like %*pbl which reads a bitmask, will save the pointer to the bitmask in the buffer. Using platform-specific means (e.g. 4500 Fifth Avenue When and how should I use a ThreadLocal variable? Are there tables of wastage rates for different fruit and veg? Why do academics stay as adjuncts for years rather than move around? The idea is not to guarantee validity, but to catch a substantial number of problems that could occur. My below code where I'm calling a stored procedure is giving a null pointer exception. This solution also ensures that theuser_data pointer is not null. The libpng library implements its own wrapper to malloc() that returns a null pointer on error or on being passed a 0-byte-length argument. very old code or C code being worked into c++ may have functions that expect the user to delete the data. versions used (SonarQube, Scanner, language analyzer) return p == NULL || (char *)p < &_etext; I was fixing some issues gathered by SonarQube when I stumbled upon the following issue: SonarQube violation: Possible null pointer dereference in ___ due to return value of called method, This error was found in the following code: else if (foo.list().length > 0) { }, I attempted to resolve this by rewriting as: else if (null != foo.list() && foo.list().length > 0) { }, foo is an instance of the File class in Java, and is directly instantiated through new File(). ability to run any cleanup processes. Which @NotNull Java annotation should I use? EXP34-C is a common consequence of ignoring function return values, but it is a distinct error, and can occur in other scenarios too. How can we prove that the supernatural or paranormal doesn't exist? I already tried to put ResponseEntity responseDto inside my try clause assigning and returning the respective value but its mandatory to return something out the try/catch. IMHO, the rule title should be changed to something less general. 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. At best, such an exception will cause abrupt program termination. 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. 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. 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. The only potential null is the return value of list(). Many platforms can support testing for those also. It's still illegal. Privacy Policy, Detect issues in your GitHub, Azure DevOps Services, Bitbucket Cloud, GitLab repositories. Since you cannot have a variable of type void, the pointer will not point to any data and therefore cannot be dereferenced. And fwstr > is dereferenced in the following codes. 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. Aaron:I suspect we are talking past each other. Hello. How handle the initialization of "responseDto" without "null" because is throwing the issue on sonar. That's true. Which ensures that the chunkdata pointer is valid, but makes no such check to the user_data pointer. All content is copyright protected. And if there is no pointer_default declaration, then the default default is ref. I suppose there is a question of "Is a pointer that points to 0 bytes valid?" The method takes a relation name r as input, executes the query "select * from r," and prints the result out in tabular format with the attribute names displayed in the table's header; the attribute names are displayed in the table's header. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. Privacy Policy, Detect issues in your GitHub, Azure DevOps Services, Bitbucket Cloud, GitLab repositories. Connect and share knowledge within a single location that is structured and easy to search. Sonar is ok. Sonar can't determine that the helper method did the null validation. Doing so will at best cause abrupt program termination, without the This cross-file approach analysis can be quite resource-consuming, and we are not ready to openly enable the feature. Trying to understand how to get this basic Fourier Series. So no checking of the length is necessary (besides preventing integer overflow, which the compliant solution does). 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. We really appreciate your help. 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. The Clang Static Analyzer already has a checker to find the null pointer dereference in code, however it is not sufficient for higher abstractions such as C++ smart pointers or optionals. Asking for help, clarification, or responding to other answers. Find centralized, trusted content and collaborate around the technologies you use most. Check whether a String is not Null and not Empty. I would also guess that pointers that point to the one-past-the-end of an array are also invalid. Powered by Discourse, best viewed with JavaScript enabled. Just because something is a pointer does not mean you should call delete . ), 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). - the incident has nothing to do with me; can I use this this way? . 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. However there is no portable way to verify that the pointer is valid, other than checking for null. Off by one error: It is the third example. But when length of A is 1, the control never reaches the else block. 3.7. This compliant solution ensures that the pointer returned by png_malloc() is not null. How do I align things in the following tabular environment? Is the God of a monotheism necessarily omnipotent? There are other problems with this code, as is noted in the rule. The value 0 for the number of bytes to copy is not what causes the UB, it's the null pointer value which triggers it. Replacing broken pins/legs on a DIP IC package, Bulk update symbol size units from mm to map units in rule-based symbology, How do you get out of a corner when plotting yourself into a corner. When I added the not null validation as sonar suggest. On many platforms, dereferencing a null pointer results inabnormal program termination, but this is not required by the standard. Cause we need throw our own Runtime Exception, well-known methods wont help. 1 Answer Sorted by: 1 Your code is ok. // <------- reported violation: NullPointerException might be thrown as 'bar' is nullable here, https://jira.sonarsource.com/browse/SONARJAVA-1490, https://groups.google.com/d/msgid/sonarqube/4752a999-246e-42c2-bbdc-8a44a5564ce9%40googlegroups.com. It could be non-null the first time but not the second time, sonar does not know this. Issues Components. context.RaiseException , (/) At this point we define size as strlen(input_str) + 1. At worst, it could expose debugging information that would be useful to an attacker, or it could allow an attacker to . static-code-analysis extern char _etext; A pointer to null (the 0 memory address) should never be dereferenced/accessed. At worst, it could expose debugging information that would be useful to an attacker or it could allow an Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. Believing that dereferencing NULL shouldn't crash the system doesn't make it true. 1 Answer Sorted by: 2 Your code needs to do something about the possible NullPointerException when some exception is caught, because in this scenario the responseDto will be null. 0 is a valid value as far as memcpy() is concerned, and malloc() has special language concerning malloc(0). An awesome tip to avoid NPE is to return empty strings or empty collections rather than null. Alternate Terms Relationships A reference to null should never be dereferenced/accessed. What is a NullPointerException, and how do I fix it?,What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them? 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. I suggest that this topic needs to include calloc() and realloc() Refer to Linux man pages online for more enlightenment about malloc(), and friends. Is the God of a monotheism necessarily omnipotent? Fixed by #1156 Contributor 94cb5f8 boris-unckel on Jul 28, 2021 9e62550 boris-unckel mentioned this issue on Jul 28, 2021 Closes #1155 - Null pointers should not be dereferenced #1156 Merged There is a missing check for the return value from . Does Java have support for multiline strings? Software Engineering Institute Site design / logo 2023 Stack Exchange Inc; user contributions licensed under CC BY-SA. It is still a pointer though, to use it you just have to cast it to another kind of pointer first. The approximation of the try catch flow is such that we consider an exception can be thrown just after the curly brace of the try. 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. Not the answer you're looking for? SONAR, SONARSOURCE, SONARLINT, SONARQUBE and SONARCLOUD are trademarks of SonarSource S.A. All other trademarks and copyrights are the property of their respective owners. rev2023.3.3.43278. )}"); In C/C++ speak, 'dereferencing' simply means getting the object that a pointer . This latter use of pointers is a combined boolean/satellite: the pointer being non-null indicates "I have this sister object", and it provides that object. ), 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'd guess WG14 has considered these questions, but I haven't until now :). That makes sense. Can I tell police to wait and call a lawyer when served with a search warrant? And the compliant solution guarantees that the pointer will be valid if the code calls memcpy(). But the problem also exists in the compliant version, so I'm not so sure that it's really compliant. Thus we should check > this kstrdup() operation. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. By clicking Accept all cookies, you agree Stack Exchange can store cookies on your device and disclose information in accordance with our Cookie Policy. It could be non-null the first time but not the second time, sonar does not know this. The nature of simulating nature: A Q&A with IBM Quantum researcher Dr. Jamie We've added a "Necessary cookies only" option to the cookie consent popup. Note that it doesn't know how to check for non-heap, non-stack. PS: I also tried the code in android studio which uses Lint and got no warnings. Additionally, if input_str is a null pointer, the call to strlen() dereferences a null pointer, also resulting in undefined behavior. The purpose of a NULL pointer is not to cause a processor exception when it is dereferenced (although that is nice to have for debugging.) 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. When exploring such methods, the engine then deduces behaviors regarding null-checking (among other things). Is there a proper earth ground point in this switch box? But when length of A is 1, the control never reaches the else block. Not the answer you're looking for? 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]. It's a modular system with the . The null pointer check for writing or dereferencing should be a compiler flag or library setting. To subscribe to this RSS feed, copy and paste this URL into your RSS reader. I'd guess null pointers are not valid, even though they point to 0 bytes. Just a few words about the rule now. Dereferencing a null pointer can lead to a denial of service. There is no legitimate reason to dereference a null pointer unless you on a rare system that maps page zero (or you intend your program to crash). validated for null in your method declaration with it: 2008-2023 SonarSource S.A., Switzerland. Much like dereferencing a dangling (or wild) pointer leads to undefined behavior, dereferencing a null pointer also leads to undefined behavior. which would allow us to systematically observe what you are having. Please direct comments on this JSR to the Spec Lead (s) Team. ssize_t (*aio_read)(struct kiocb *, char __user *, size_t . NullPointerException is thrown when program attempts to use an object reference that has the null value. If not, this might be a bug. There is no guarantee that subsequent invocations are returning the same value, thats why issue is raised. SonarJava Version 5.9.2 (build 16552). Thanks for the feedback. A null pointer stores a defined value, but one that is defined by the environment to not be a valid address for any member or object. My code is GPL licensed, can I issue a license to have my code be distributed in a specific MIT licensed project? What is a serialVersionUID and why should I use it? Removing the check "exception != null" raises S2259 "Null pointers should not be dereferenced" on "throw exception". We can get a reference to point to null in the following ways: "uninitialized" reference type variables variables which are initialized with nulls and are assigned their real value afterward. When B is null, The control reaches inside the main if block only when length of A is 1. raiseException() return, Sonar (in the meantime, in case of any other false-positive suspicion, make sure to check those latest versions as bunch of improvements are regularly released). Software project. Agreed. You need to benchmark. Making statements based on opinion; back them up with references or personal experience. Calls to extension methods are not reported because they can still operate on null values. which version of SonarQube are you using? To subscribe to this RSS feed, copy and paste this URL into your RSS reader. The correct idiom is to only allocate storage if the pointer is currently NULL. sonarLint (3.2.) Null pointer should not be dereferenced . The solution that I recommend is not work with null returns or variables on Java, try to avoid it. Connect and share knowledge within a single location that is structured and easy to search. Recovering from a blunder I made while emailing a professor. If the project is not compiled, and without sonar.java.binaries whether the white list takes effect? But even with this, the concerned object it tagged as a possible NullPointerException problem. It also adds assertions to document that certain other pointers must not be null. How to use Slater Type Orbitals as a basis functions in matrix method correctly? Now, you can find the list of whitelisted methods here. You're in a company-managed project. NULL vs Uninitialized pointer - An uninitialized pointer stores an undefined value. Good question! Rule squid:S2259 is based on a Symbolic Execution (SE) engine. To be precise, once length is changed to a size_t and cannot take negative values, it cannot have an invalid value. New replies are no longer allowed. "After the incident", I started to be more careful not to trip over things.