Re: [syzbot] [io-uring?] general protection fault in __io_remove_buffers

[Pavel Begunkov]

On 7/18/24 02:20, syzbot wrote:
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    d67978318827 Merge tag 'x86_cpu_for_v6.11_rc1' of git://gi..
> git tree:       upstream
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1178e9e9980000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=e206d588252bd3ff
> dashboard link: https://syzkaller.appspot.com/bug?extid=2074b1a3d447915c6f1c
> 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=10e07d9e980000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16adf045980000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/f34b31760156/disk-d6797831.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/a92e51d8d32e/vmlinux-d6797831.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/000a6a162550/bzImage-d6797831.xz
>
> The issue was bisected to:
>
> commit 87585b05757dc70545efb434669708d276125559
> Author: Jens Axboe <axboe@xxxxxxxxx>
> Date:   Wed Mar 13 02:24:21 2024 +0000
>
>      io_uring/kbuf: use vm_insert_pages() for mmap'ed pbuf ring
Easily reproducible, the diff helps

#syz test:


diff --git a/io_uring/kbuf.c b/io_uring/kbuf.c
index d2945c9c812b..c95dc1736dd9 100644
--- a/io_uring/kbuf.c
+++ b/io_uring/kbuf.c
@@ -657,8 +657,10 @@ static int io_alloc_pbuf_ring(struct io_ring_ctx *ctx,
 	ring_size = reg->ring_entries * sizeof(struct io_uring_buf_ring);
 
 	bl->buf_ring = io_pages_map(&bl->buf_pages, &bl->buf_nr_pages, ring_size);
-	if (!bl->buf_ring)
+	if (IS_ERR(bl->buf_ring)) {
+		bl->buf_ring = NULL;
 		return -ENOMEM;
+	}
 
 	bl->is_buf_ring = 1;
 	bl->is_mmap = 1;