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Subject: Re: general protection fault in io_uring_show_cred
To:     syzbot <syzbot+a6d494688cdb797bdfce@syzkaller.appspotmail.com>,
        io-uring@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com,
        viro@zeniv.linux.org.uk
References: <0000000000003afa6905b35e6386@google.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <1390bb94-a400-8e17-3c39-06c38277f091@kernel.dk>
Date:   Thu, 5 Nov 2020 09:49:31 -0700
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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 <axboe@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