CVE-2023-52836

In the Linux kernel, the following vulnerability has been resolved:

locking/ww_mutex/test: Fix potential workqueue corruption

In some cases running with the test-ww_mutex code, I was seeing odd behavior where sometimes it seemed flush_workqueue was returning before all the work threads were finished.

Often this would cause strange crashes as the mutexes would be freed while they were being used.

Looking at the code, there is a lifetime problem as the controlling thread that spawns the work allocates the struct stress structures that are passed to the workqueue threads. Then when the workqueue threads are finished, they free the stress struct that was passed to them.

Unfortunately the workqueue work_struct node is in the stress struct. Which means the work_struct is freed before the work thread returns and while flush_workqueue is waiting.

It seems like a better idea to have the controlling thread both allocate and free the stress structures, so that we can be sure we dont corrupt the workqueue by freeing the structure prematurely.

So this patch reworks the test to do so, and with this change I no longer see the early flush_workqueue returns.

Weakness

The product writes data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer.

• Be wary that a language’s interface to native code may still be subject to overflows, even if the language itself is theoretically safe.

• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.

• Examples include the Safe C String Library (SafeStr) by Messier and Viega [REF-57], and the Strsafe.h library from Microsoft [REF-56]. These libraries provide safer versions of overflow-prone string-handling functions.

• Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.

• D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.

• Consider adhering to the following rules when allocating and managing an application’s memory:

• Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.

• Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.

• For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].

• Use a CPU and operating system that offers Data Execution Protection (using hardware NX or XD bits) or the equivalent techniques that simulate this feature in software, such as PaX [REF-60] [REF-61]. These techniques ensure that any instruction executed is exclusively at a memory address that is part of the code segment.

• For more information on these techniques see D3-PSEP (Process Segment Execution Prevention) from D3FEND [REF-1336].

References

• https://git.kernel.org/stable/c/304a2c4aad0fff887ce493e4197bf9cbaf394479
• https://git.kernel.org/stable/c/9ed2d68b3925145f5f51c46559484881d6082f75
• https://git.kernel.org/stable/c/bccdd808902f8c677317cec47c306e42b93b849e
• https://git.kernel.org/stable/c/c56df79d68677cf062da1b6e3b33e74299a92dfc
• https://git.kernel.org/stable/c/d4d37c9e6a4dbcca958dabd99216550525c7e389
• https://git.kernel.org/stable/c/d8267cabbe1bed15ccf8b0e684c528bf8eeef715
• https://git.kernel.org/stable/c/dcd85e3c929368076a7592b27f541e0da8b427f5
• https://git.kernel.org/stable/c/e36407713163363e65566e7af0abe207d5f59a0c
• https://git.kernel.org/stable/c/e89d0ed45a419c485bae999426ecf92697cbdda3
• https://git.kernel.org/stable/c/304a2c4aad0fff887ce493e4197bf9cbaf394479
• https://git.kernel.org/stable/c/9ed2d68b3925145f5f51c46559484881d6082f75
• https://git.kernel.org/stable/c/bccdd808902f8c677317cec47c306e42b93b849e
• https://git.kernel.org/stable/c/c56df79d68677cf062da1b6e3b33e74299a92dfc
• https://git.kernel.org/stable/c/d4d37c9e6a4dbcca958dabd99216550525c7e389
• https://git.kernel.org/stable/c/d8267cabbe1bed15ccf8b0e684c528bf8eeef715
• https://git.kernel.org/stable/c/dcd85e3c929368076a7592b27f541e0da8b427f5
• https://git.kernel.org/stable/c/e36407713163363e65566e7af0abe207d5f59a0c
• https://git.kernel.org/stable/c/e89d0ed45a419c485bae999426ecf92697cbdda3