5.5 - CVE-2024-56613

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

sched/numa: fix memory leak due to the overwritten vma->numab_state

[Problem Description] When running the hackbench program of LTP, the following memory leak is reported by kmemleak.

# /opt/ltp/testcases/bin/hackbench 20 thread 1000
Running with 20*40 (== 800) tasks.

# dmesg | grep kmemleak
...
kmemleak: 480 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
kmemleak: 665 new suspected memory leaks (see /sys/kernel/debug/kmemleak)

# cat /sys/kernel/debug/kmemleak
unreferenced object 0xffff888cd8ca2c40 (size 64):
comm "hackbench", pid 17142, jiffies 4299780315
hex dump (first 32 bytes):
ac 74 49 00 01 00 00 00 4c 84 49 00 01 00 00 00 .tI.....L.I.....
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
backtrace (crc bff18fd4):
[] __kmalloc_cache_noprof+0x2f9/0x3f0
[] task_numa_work+0x725/0xa00
[] task_work_run+0x58/0x90
[] syscall_exit_to_user_mode+0x1c8/0x1e0
[] do_syscall_64+0x85/0x150
[] entry_SYSCALL_64_after_hwframe+0x76/0x7e
...

This issue can be consistently reproduced on three different servers:
* a 448-core server
* a 256-core server
* a 192-core server

[Root Cause] Since multiple threads are created by the hackbench program (along with the command argument 'thread'), a shared vma might be accessed by two or more cores simultaneously. When two or more cores observe that vma->numab_state is NULL at the same time, vma->numab_state will be overwritten.

Although current code ensures that only one thread scans the VMAs in a single 'numa_scan_period', there might be a chance for another thread to enter in the next 'numa_scan_period' while we have not gotten till numab_state allocation [1].

Note that the command `/opt/ltp/testcases/bin/hackbench 50 process 1000` cannot the reproduce the issue. It is verified with 200+ test runs.

[Solution] Use the cmpxchg atomic operation to ensure that only one thread executes the vma->numab_state assignment.

[1] https://lore.kernel.org/lkml/1794be3c-358c-4cdc-a43d-a1f841d91ef7@amd.com/