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/
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
Eric
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Sun, Dec 19, 2021 at 11:58:41PM -0600, Eric W. Biederman wrote:
Qian Cai [off-list ref] writes:
quoted
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/
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:
quoted
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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel