Re: [syzbot] [io-uring?] KASAN: null-ptr-deref Write in sys_io_uring_register

[Jens Axboe]

On 12/4/24 6:56 AM, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    c245a7a79602 Add linux-next specific files for 20241203
> git tree:       linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=10ae840f980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=af3fe1d01b9e7b7
> dashboard link: https://syzkaller.appspot.com/bug?extid=092bbab7da235a02a03a
> compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=14a448df980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=15cca330580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/8cc90a2ea120/disk-c245a7a7.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/0f6b1a1a0541/vmlinux-c245a7a7.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9fa3eac09ddc/bzImage-c245a7a7.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+092bbab7da235a02a03a@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
> BUG: KASAN: null-ptr-deref in atomic_long_sub_and_test include/linux/atomic/atomic-instrumented.h:4521 [inline]
> BUG: KASAN: null-ptr-deref in put_cred_many include/linux/cred.h:255 [inline]
> BUG: KASAN: null-ptr-deref in put_cred include/linux/cred.h:269 [inline]
> BUG: KASAN: null-ptr-deref in io_unregister_personality io_uring/register.c:82 [inline]
> BUG: KASAN: null-ptr-deref in __io_uring_register io_uring/register.c:698 [inline]
> BUG: KASAN: null-ptr-deref in __do_sys_io_uring_register io_uring/register.c:902 [inline]
> BUG: KASAN: null-ptr-deref in __se_sys_io_uring_register+0x1227/0x3b60 io_uring/register.c:879
> Write of size 8 at addr 0000000000000406 by task syz-executor274/5828
> 
> CPU: 1 UID: 0 PID: 5828 Comm: syz-executor274 Not tainted 6.13.0-rc1-next-20241203-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
> Call Trace:
>  <TASK>
>  __dump_stack lib/dump_stack.c:94 [inline]
>  dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
>  print_report+0xe8/0x550 mm/kasan/report.c:492
>  kasan_report+0x143/0x180 mm/kasan/report.c:602
>  kasan_check_range+0x282/0x290 mm/kasan/generic.c:189
>  instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>  atomic_long_sub_and_test include/linux/atomic/atomic-instrumented.h:4521 [inline]
>  put_cred_many include/linux/cred.h:255 [inline]
>  put_cred include/linux/cred.h:269 [inline]
>  io_unregister_personality io_uring/register.c:82 [inline]
>  __io_uring_register io_uring/register.c:698 [inline]
>  __do_sys_io_uring_register io_uring/register.c:902 [inline]
>  __se_sys_io_uring_register+0x1227/0x3b60 io_uring/register.c:879
>  do_syscall_x64 arch/x86/entry/common.c:52 [inline]
>  do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f65bbcb03a9
> Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007ffe8fac7478 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
> RAX: ffffffffffffffda RBX: 000000000000371d RCX: 00007f65bbcb03a9
> RDX: 0000000000000000 RSI: 000000000000000a RDI: 0000000000000003
> RBP: 0000000000000003 R08: 00000000000ac5f8 R09: 00000000000ac5f8
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007ffe8fac7648 R14: 0000000000000001 R15: 0000000000000001
>  </TASK>
> ==================================================================

Not sure what's going on with -next, but this looks like nonsense - we
store a valid pointer in the xarry, and then attempt to delete an
invalid index which then returns a totally garbage pointer!? I'll check
what is in -next, but this very much does not look like an io_uring
issue.

-- 
Jens Axboe