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/[email protected]/