CVE-2025-21726

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

padata: avoid UAF for reorder_work

Although the previous patch can avoid ps and ps UAF for _do_serial, it can not avoid potential UAF issue for reorder_work. This issue can happen just as below:

crypto_request crypto_request crypto_del_alg padata_do_serial … padata_reorder // processes all remaining // requests then breaks while (1) { if (!padata) break; … }

			padata_do_serial
			  // new request added
			  list_add
// sees the new request
queue_work(reorder_work)
			  padata_reorder
			    queue_work_on(squeue->work)

…

			<kworker context>
			padata_serial_worker
			// completes new request,
			// no more outstanding
			// requests

						crypto_del_alg
						  // free pd

To avoid UAF for reorder_work, get pd ref before put reorder_work into the serial_wq and put pd ref until the serial_wq finish.

Weakness

Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.

Affected Software

Extended Description

The use of previously-freed memory can have any number of adverse consequences, ranging from the corruption of valid data to the execution of arbitrary code, depending on the instantiation and timing of the flaw. The simplest way data corruption may occur involves the system’s reuse of the freed memory. Use-after-free errors have two common and sometimes overlapping causes:

In this scenario, the memory in question is allocated to another pointer validly at some point after it has been freed. The original pointer to the freed memory is used again and points to somewhere within the new allocation. As the data is changed, it corrupts the validly used memory; this induces undefined behavior in the process. If the newly allocated data happens to hold a class, in C++ for example, various function pointers may be scattered within the heap data. If one of these function pointers is overwritten with an address to valid shellcode, execution of arbitrary code can be achieved.

Potential Mitigations

References

• https://git.kernel.org/stable/c/4c6209efea2208597dbd3e52dc87a0d1a8f2dbe1
• https://git.kernel.org/stable/c/6f45ef616775b0ce7889b0f6077fc8d681ab30bc
• https://git.kernel.org/stable/c/7000507bb0d2ceb545c0a690e0c707c897d102c2
• https://git.kernel.org/stable/c/8ca38d0ca8c3d30dd18d311f1a7ec5cb56972cac
• https://git.kernel.org/stable/c/a54091c24220a4cd847d5b4f36d678edacddbaf0
• https://git.kernel.org/stable/c/dd7d37ccf6b11f3d95e797ebe4e9e886d0332600
• https://git.kernel.org/stable/c/f4f1b1169fc3694f9bc3e28c6c68dbbf4cc744c0