Messages in this thread Patch in this message | | | Date | Tue, 21 Dec 2021 14:09:37 +0100 | From | Alexey Gladkov <> | Subject | Re: BUG: KASAN: use-after-free in dec_rlimit_ucounts |
| |
On Sun, Dec 19, 2021 at 11:58:41PM -0600, Eric W. Biederman wrote: > Qian Cai <quic_qiancai@quicinc.com> writes: > > > On Wed, Nov 24, 2021 at 04:49:19PM -0500, Qian Cai wrote: > >> 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/ > > > > 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 still can't reproduce :(
> I didn't watch so I don't know if it was 5 minutes but I do know it took > less than an hour.
--- a/kernel/ucount.c +++ b/kernel/ucount.c @@ -209,6 +209,7 @@ void put_ucounts(struct ucounts *ucounts)
if (atomic_dec_and_lock_irqsave(&ucounts->count, &ucounts_lock, flags)) { hlist_del_init(&ucounts->node); + ucounts->ns = NULL; spin_unlock_irqrestore(&ucounts_lock, flags); kfree(ucounts); } Does the previous hack increase the likelihood of an error being triggered?
> 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 > > Eric >
-- Rgrds, legion
| |