Re: BUG: KASAN: use-after-free in dec_rlimit_ucounts
From: Eric W. Biederman <hidden>
Date: 2021-12-20 05:59:18
Also in:
lkml
Qian Cai [off-list ref] writes:
On Wed, Nov 24, 2021 at 04:49:19PM -0500, Qian Cai wrote:quoted
Hmm, I don't know if that or it is just this platfrom is lucky to trigger the race condition quickly, but I can't reproduce it on x86 so far. I am Cc'ing a few arm64 people to see if they have spot anything I might be missing. The original bug report is here: https://lore.kernel.org/lkml/YZV7Z+yXbsx9p3JN@fixkernel.com/ (local)Okay, I am finally able to reproduce this on x86_64 with the latest mainline as well by setting CONFIG_USER_NS and KASAN on the top of defconfig (I did not realize it did not select CONFIG_USER_NS in the first place). Anyway, it still took less than 5-minute by running: $ trinity -C 48
It took me a while to get to the point of reproducing this but I can confirm I see this with 2 core VM, running 5.16.0-rc4. Running trinity 2019.06 packaged in debian 11. I didn't watch so I don't know if it was 5 minutes but I do know it took less than an hour. Now I am puzzled why there are not other reports of problems. Now to start drilling down to figure out why the user namespace was freed early. ---- The failure I got looked like:
BUG: KASAN: use-after-free in dec_rlimit_ucounts+0x7b/0xb0 Read of size 8 at addr ffff88800b7dd018 by task trinity-c3/67982 CPU: 1 PID: 67982 Comm: trinity-c3 Tainted: G O 5.16.0-rc4 #1 Hardware name: Xen HVM domU, BIOS 4.8.5-35.fc25 08/25/2021 Call Trace: <TASK> dump_stack_lvl+0x48/0x5e print_address_descrtion.constprop.0+0x1f/0x140 ? dec_rlimit_ucounts+0x7b/0xb0 ? dec_rlimit_ucounts+0x7b/0xb0 kasan_report.cold+0x7f/0xe0 ? _raw_spin_lock+0x7f/0x11b ? dec_rlimit_ucounts+0x7b/0xb0 dec_rlimit_ucounts+0x7b/0xb0 mqueue_evict_inode+0x417/0x590 ? perf_trace_global_dirty_state+0x350/0x350 ? __x64_sys_mq_unlink+0x250/0x250 ? _raw_spin_lock_bh+0xe0/0xe0 ? _raw_spin_lock_bh+0xe0/0xe0 evict+0x155/0x2a0 __x64_sys_mq_unlink+0x1a7/0x250 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f0505ebc9b9 Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 00 0f 1f 44 00 00 48 89 .... Allocated by task 67717 Freed by task 6027 The buggy address belongs to the object at ffff88800b7dce38 which belongs to the cache user_namespace of size 600 The buggy address is located 480 bytes inside of 600-byte region [ffff88800b7dce38, ffff88800b7dd090] The buggy address belongs to the page: trinity: Detected kernel tainting. Last seed was 1891442794
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