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>] dup_task_struct+0x30/0x540

[<00000000c5ca0f0b>] copy_process+0x3d9/0x50e0

[<00000000ced59777>] kernel_clone+0xb0/0x770

[<00000000a50befdc>] __do_sys_clone+0xb6/0xf0

[<000000001dbf2008>] do_syscall_64+0x5d/0xf0

[<00000000552900ff>] entry_SYSCALL_64_after_hwframe+0x6e/0x76

The issue occurs in start_dl_timer(), which increments the task_struct

reference count and sets a timer. The timer callback, dl_task_timer,

is supposed to decrement the reference count upon expiration. However,

if enqueue_task_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.