Messages in this thread | | | Date | Thu, 18 Nov 2021 15:32:33 -0500 | From | Qian Cai <> | Subject | Re: BUG: KASAN: use-after-free in dec_rlimit_ucounts |
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On Thu, Nov 18, 2021 at 01:46:05PM -0600, Eric W. Biederman wrote: > Is it possible? Yes it is possible. That is one place where > a use-after-free has shown up and I expect would show up in the > future. > > That said it is hard to believe there is still a user-after-free in the > code. We spent the last kernel development cycle pouring through and > correcting everything we saw until we ultimately found one very subtle > use-after-free. > > If you have a reliable reproducer that you can share, we can look into > this and see if we can track down where the reference count is going > bad. > > It tends to take instrumenting the entire life cycle every increment and > every decrement and then pouring through the logs to track down a > use-after-free. Which is not something we can really do without a > reproducer.
The reproducer is just to run trinity by an unprivileged user on defconfig with KASAN enabled (On linux-next, you can do "make defconfig debug.conf" [1], but dont think other debugging options are relevent here.)
$ trinity -C 31 -N 10000000
It is always reproduced on an arm64 server here within 5-minute so far. Some debugging progress so far. BTW, this could happen on user_shm_unlock() path as well.
Call trace: dec_rlimit_ucounts user_shm_unlock (inlined by) user_shm_unlock at mm/mlock.c:854 shmem_lock shmctl_do_lock ksys_shmctl.constprop.0 __arm64_sys_shmctl invoke_syscall el0_svc_common.constprop.0 do_el0_svc el0_svc el0t_64_sync_handler el0t_64_sync
I noticed in dec_rlimit_ucounts(), dec == 0 and type == UCOUNT_RLIMIT_MEMLOCK.
[1] https://lore.kernel.org/lkml/20211115134754.7334-1-quic_qiancai@quicinc.com/
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