CVE-2024-41023

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

sched/deadline: Fix task_struct reference leak

During the execution of the following stress test with linux-rt:

stress-ng --cyclic 30 --timeout 30 --minimize --quiet

kmemleak frequently reported a memory leak concerning the task_struct:

unreferenced object 0xffff8881305b8000 (size 16136): comm "stress-ng", pid 614, jiffies 4294883961 (age 286.412s) object hex dump (first 32 bytes): 02 40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 .@.............. 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ debug hex dump (first 16 bytes): 53 09 00 00 00 00 00 00 00 00 00 00 00 00 00 00 S............... backtrace: [<00000000046b6790>] duptaskstruct+0x30/0x540 [<00000000c5ca0f0b>] copyprocess+0x3d9/0x50e0 [<00000000ced59777>] kernelclone+0xb0/0x770 [<00000000a50befdc>] _dosysclone+0xb6/0xf0 [<000000001dbf2008>] dosyscall64+0x5d/0xf0 [<00000000552900ff>] entrySYSCALL64after_hwframe+0x6e/0x76

The issue occurs in startdltimer(), which increments the taskstruct reference count and sets a timer. The timer callback, dltasktimer, is supposed to decrement the reference count upon expiration. However, if enqueuetask_dl() is called before the timer expires and cancels it, the reference count is not decremented, leading to the leak.

This patch fixes the reference leak by ensuring the task_struct reference count is properly decremented when the timer is canceled.