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

[Tamir Duberstein <tamird@gmail.com>]

On Wed, Dec 4, 2024 at 10:10 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> On 12/4/24 8:01 AM, Jens Axboe wrote:
> > 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@syzkaller.appspotmail.com
> >>
> >> ==================================================================
> >> 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.
>
> Took a quick look, and it's this patch:
>
> commit d2e88c71bdb07f1e5ccffbcc80d747ccd6144b75
> Author: Tamir Duberstein <tamird@gmail.com>
> Date:   Tue Nov 12 14:25:37 2024 -0500
>
>     xarray: extract helper from __xa_{insert,cmpxchg}
>
> in the current -next tree. Adding a few folks who might be interested.
>
> --
> Jens Axboe

Yep, looks broken. I believe the missing bit is

diff --git a/lib/xarray.c b/lib/xarray.c
index 2af86bede3c1..5da8d18899a1 100644
--- a/lib/xarray.c
+++ b/lib/xarray.c
@@ -1509,7 +1509,7 @@ static void *xas_result(struct xa_state *xas, void *curr)
 void *__xa_erase(struct xarray *xa, unsigned long index)
 {
  XA_STATE(xas, xa, index);
- return xas_result(&xas, xas_store(&xas, NULL));
+ return xas_result(&xas, xa_zero_to_null(xas_store(&xas, NULL)));
 }
 EXPORT_SYMBOL(__xa_erase);

This would explain deletion of a reserved entry returning
`XA_ZERO_ENTRY` rather than `NULL`.

My apologies for this breakage. Should I send a new version? A new
"fixes" patch?
tamird