general protection fault in io_uring_show_cred

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 4ef8451b Merge tag 'perf-tools-for-v5.10-2020-11-03' of gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=12bf23a8500000
kernel config: https://syzkaller.appspot.com/x/.config?x=61033507391c77ff
dashboard link: https://syzkaller.appspot.com/bug?extid=a6d494688cdb797bdfce
compiler: gcc (GCC) 10.1.0-syz 20200507
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11022732500000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13649314500000

The issue was bisected to:

commit 1e6fa5216a0e59ef02e8b6b40d553238a3b81d49
Author: Jens Axboe <ax...@kernel.dk>
Date: Thu Oct 15 14:46:24 2020 +0000

io_uring: COW io_identity on mismatch

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14295fa8500000
final oops: https://syzkaller.appspot.com/x/report.txt?x=16295fa8500000
console output: https://syzkaller.appspot.com/x/log.txt?x=12295fa8500000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a6d494...@syzkaller.appspotmail.com
Fixes: 1e6fa5216a0e ("io_uring: COW io_identity on mismatch")

general protection fault, probably for non-canonical address 0xdffffc04422cfb38: 0000 [#1] PREEMPT SMP KASAN
KASAN: probably user-memory-access in range [0x000000221167d9c0-0x000000221167d9c7]
CPU: 0 PID: 8480 Comm: syz-executor292 Not tainted 5.10.0-rc2-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:io_uring_show_cred+0x32f/0x5f0 fs/io_uring.c:8922
Code: 3c 02 00 0f 85 a8 02 00 00 49 8b ae a0 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 4d 04 48 89 ca 48 89 4c 24 18 48 c1 ea 03 <0f> b6 14 02 48 89 c8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 e4
RSP: 0018:ffffc900015ff9f0 EFLAGS: 00010203
RAX: dffffc0000000000 RBX: ffff8880213f4c00 RCX: 000000221167d9c4
RDX: 00000004422cfb38 RSI: ffffffff81d32adc RDI: ffff888014b101a0
RBP: 000000221167d9c0 R08: 0000000000000001 R09: ffff8880272840ce
R10: ffffed1004e50819 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8880136c4cb8 R14: ffff888014b10100 R15: ffffffff8b1fe940
FS: 0000000001182880(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000455310 CR3: 000000001b604000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
idr_for_each+0x113/0x220 lib/idr.c:208
__io_uring_show_fdinfo fs/io_uring.c:8974 [inline]
io_uring_show_fdinfo+0x923/0xda0 fs/io_uring.c:8996
seq_show+0x4a8/0x700 fs/proc/fd.c:65
seq_read+0x432/0x1070 fs/seq_file.c:208
do_loop_readv_writev fs/read_write.c:761 [inline]
do_loop_readv_writev fs/read_write.c:748 [inline]
do_iter_read+0x48e/0x6e0 fs/read_write.c:803
vfs_readv+0xe5/0x150 fs/read_write.c:921
do_preadv fs/read_write.c:1013 [inline]
__do_sys_preadv fs/read_write.c:1063 [inline]
__se_sys_preadv fs/read_write.c:1058 [inline]
__x64_sys_preadv+0x231/0x310 fs/read_write.c:1058
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x4403a9
Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 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 0f 83 db 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fff45cb17f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000127
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 00000000004403a9
RDX: 0000000000000333 RSI: 00000000200017c0 RDI: 0000000000000004
RBP: 00000000006ca018 R08: 0000000000000000 R09: 65732f636f72702f
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401c10
R13: 0000000000401ca0 R14: 0000000000000000 R15: 0000000000000000
Modules linked in:
---[ end trace 2f3a282977161035 ]---
RIP: 0010:io_uring_show_cred+0x32f/0x5f0 fs/io_uring.c:8922
Code: 3c 02 00 0f 85 a8 02 00 00 49 8b ae a0 00 00 00 48 b8 00 00 00 00 00 fc ff df 48 8d 4d 04 48 89 ca 48 89 4c 24 18 48 c1 ea 03 <0f> b6 14 02 48 89 c8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 e4
RSP: 0018:ffffc900015ff9f0 EFLAGS: 00010203
RAX: dffffc0000000000 RBX: ffff8880213f4c00 RCX: 000000221167d9c4
RDX: 00000004422cfb38 RSI: ffffffff81d32adc RDI: ffff888014b101a0
RBP: 000000221167d9c0 R08: 0000000000000001 R09: ffff8880272840ce
R10: ffffed1004e50819 R11: 0000000000000000 R12: 0000000000000001
R13: ffff8880136c4cb8 R14: ffff888014b10100 R15: ffffffff8b1fe940
FS: 0000000001182880(0000) GS:ffff8880b9e00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000455310 CR3: 000000001b604000 CR4: 00000000001506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400


---
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[Jens Axboe]

On 11/5/20 9:14 AM, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 4ef8451b Merge tag 'perf-tools-for-v5.10-2020-11-03' of gi..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=12bf23a8500000
> kernel config: https://syzkaller.appspot.com/x/.config?x=61033507391c77ff
> dashboard link: https://syzkaller.appspot.com/bug?extid=a6d494688cdb797bdfce
> compiler: gcc (GCC) 10.1.0-syz 20200507
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11022732500000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13649314500000
>
> The issue was bisected to:
>
> commit 1e6fa5216a0e59ef02e8b6b40d553238a3b81d49
> Author: Jens Axboe <ax...@kernel.dk>
> Date: Thu Oct 15 14:46:24 2020 +0000
>
> io_uring: COW io_identity on mismatch

Gah, stupid braino in that patch. Below should fix it.

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 3d489cf31926..29f1417690d5 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8974,7 +8974,8 @@ SYSCALL_DEFINE6(io_uring_enter, unsigned int, fd, u32, to_submit,
#ifdef CONFIG_PROC_FS
static int io_uring_show_cred(int id, void *p, void *data)
{
- const struct cred *cred = p;
+ struct io_identity *iod = p;
+ const struct cred *cred = iod->creds;
struct seq_file *m = data;
struct user_namespace *uns = seq_user_ns(m);
struct group_info *gi;

--
Jens Axboe