[syzbot] [lsm?] [keyrings?] KCSAN: data-race in __se_sys_keyctl / key_task_permission (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8a9c6c40432e Merge tag 'io_uring-6.10-20240703' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=113817ae980000
kernel config: https://syzkaller.appspot.com/x/.config?x=5b9537cd00be479e
dashboard link: https://syzkaller.appspot.com/bug?extid=8c446f45cf5815e9110a
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f01153f3ec8e/disk-8a9c6c40.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/04b88663a824/vmlinux-8a9c6c40.xz
kernel image: https://storage.googleapis.com/syzbot-assets/63c518cc63c5/bzImage-8a9c6c40.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+8c446f...@syzkaller.appspotmail.com

==================================================================
BUG: KCSAN: data-race in __se_sys_keyctl / key_task_permission

write to 0xffff88812277dd70 of 4 bytes by task 19442 on cpu 0:
keyctl_setperm_key security/keys/keyctl.c:1098 [inline]
__do_sys_keyctl security/keys/keyctl.c:1926 [inline]
__se_sys_keyctl+0xab5/0xbb0 security/keys/keyctl.c:1874
__x64_sys_keyctl+0x67/0x80 security/keys/keyctl.c:1874
x64_sys_call+0x2bf5/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:251
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

read to 0xffff88812277dd70 of 4 bytes by task 19441 on cpu 1:
key_task_permission+0x14a/0x2c0 security/keys/permission.c:55
lookup_user_key+0x9ea/0xdf0 security/keys/process_keys.c:803
keyctl_setperm_key security/keys/keyctl.c:1083 [inline]
__do_sys_keyctl security/keys/keyctl.c:1926 [inline]
__se_sys_keyctl+0x829/0xbb0 security/keys/keyctl.c:1874
__x64_sys_keyctl+0x67/0x80 security/keys/keyctl.c:1874
x64_sys_call+0x2bf5/0x2d70 arch/x86/include/generated/asm/syscalls_64.h:251
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xc9/0x1c0 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

value changed: 0x3d010000 -> 0x00000000

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 19441 Comm: syz.1.4799 Tainted: G W 6.10.0-rc6-syzkaller-00067-g8a9c6c40432e #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/07/2024
==================================================================


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[Dmitry Vyukov]

The code in key_task_permission() looks fishy if it can race with
key->perm updates.
There is possibility for TOCTOU and unintentional re-reads of the field.