About vulnerability

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): [<ffffffff81419a89>] __kmalloc_cache_noprof+0x2f9/0x3f0 [<ffffffff8113f715>] task_numa_work+0x725/0xa00 [<ffffffff8110f878>] task_work_run+0x58/0x90 [<ffffffff81ddd9f8>] syscall_exit_to_user_mode+0x1c8/0x1e0 [<ffffffff81dd78d5>] do_syscall_64+0x85/0x150 [<ffffffff81e0012b>] 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/[email protected]/

Affected product:

AlmaLinux 9.2 ESU , TuxCare 9.6 ESU

Affected packages:

kernel @ 5.14.0 (+1 more)

Live-patch status from KernelCare for each operating system.