[syzbot] KCSAN: data-race in assoc_array_apply_edit / search_nested_keyrings

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 5e321ded Merge tag 'for-5.13/parisc' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=111cafb9d00000
kernel config: https://syzkaller.appspot.com/x/.config?x=a4da2ebcb6e8f526
dashboard link: https://syzkaller.appspot.com/bug?extid=e4eb6db47eb0f80308c6
compiler: Debian clang version 11.0.1-2

Unfortunately, I don't have any reproducer for this issue yet.

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+e4eb6d...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in assoc_array_apply_edit / search_nested_keyrings

write to 0xffff8881065ffc10 of 8 bytes by task 30966 on cpu 1:
assoc_array_apply_edit+0x3e/0x660 lib/assoc_array.c:1357
__key_link+0x8a/0xc0 security/keys/keyring.c:1372
__key_instantiate_and_link+0x15b/0x290 security/keys/key.c:459
key_create_or_update+0x750/0x990 security/keys/key.c:941
__do_sys_add_key security/keys/keyctl.c:134 [inline]
__se_sys_add_key+0x26f/0x300 security/keys/keyctl.c:74
__x64_sys_add_key+0x63/0x70 security/keys/keyctl.c:74
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

read to 0xffff8881065ffc10 of 8 bytes by task 30971 on cpu 0:
search_nested_keyrings+0x34f/0x920 security/keys/keyring.c:751
keyring_search_rcu+0xf4/0x180 security/keys/keyring.c:922
search_cred_keyrings_rcu+0x135/0x240 security/keys/process_keys.c:480
search_process_keyrings_rcu security/keys/process_keys.c:544 [inline]
lookup_user_key+0xab6/0xd40 security/keys/process_keys.c:762
__do_sys_add_key security/keys/keyctl.c:126 [inline]
__se_sys_add_key+0x23a/0x300 security/keys/keyctl.c:74
__x64_sys_add_key+0x63/0x70 security/keys/keyctl.c:74
do_syscall_64+0x4a/0x90 arch/x86/entry/common.c:47
entry_SYSCALL_64_after_hwframe+0x44/0xae

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 30971 Comm: syz-executor.1 Not tainted 5.12.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
==================================================================


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[Marco Elver]

Hello,

I found this interesting because the code around
security/keys/keyring.c:751 is diligent in marking concurrency
accesses with READ_ONCE(). So on the off-chance there is unexpected
concurrency here, I thought it'd be worth double-checking as I wasn't
able to conclude if this is just missing a READ_ONCE().

Thank you!

[Eric Biggers]

It looks more like the problem is missing WRITE_ONCE(), not READ_ONCE().

smp_store_release() would also handle this properly, without the need for the
explicit smp_wmb().

- Eric

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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.