linux-kernel - Re: [syzbot] [lsm?] [keyrings?] KCSAN: data-race in __se_sys_keyctl / key_task

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Message-ID: <CACT4Y+a1QqOO7XbZrTkppopg3hiUdBkpQLwN8+67PmHJcRHJsQ@mail.gmail.com>
Date: Thu, 4 Jul 2024 16:38:58 +0200
From: Dmitry Vyukov <dvyukov@...gle.com>
To: syzbot <syzbot+8c446f45cf5815e9110a@...kaller.appspotmail.com>
Cc: dhowells@...hat.com, jarkko@...nel.org, jmorris@...ei.org, 
	keyrings@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-security-module@...r.kernel.org, paul@...l-moore.com, serge@...lyn.com, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [lsm?] [keyrings?] KCSAN: data-race in __se_sys_keyctl /
 key_task_permission (3)

On Thu, 4 Jul 2024 at 16:18, syzbot
<syzbot+8c446f45cf5815e9110a@...kaller.appspotmail.com> wrote:
>
> 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+8c446f45cf5815e9110a@...kaller.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
> ==================================================================

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.