Re: [syzbot] KASAN: use-after-free Read in ucma_destroy_private_ctx

[Leon Romanovsky]

On Mon, Jan 03, 2022 at 09:05:16AM -0800, syzbot wrote:
> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    a8ad9a2434dc Merge tag 'efi-urgent-for-v5.16-2' of git://g..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=10cf5253b00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=1a86c22260afac2f
> dashboard link: https://syzkaller.appspot.com/bug?extid=e3f96c43d19782dd14a7
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> 
> Unfortunately, I don't have any reproducer for this issue yet.
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+e3f96c43d19782dd14a7@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ==================================================================
> BUG: KASAN: use-after-free in ucma_cleanup_multicast drivers/infiniband/core/ucma.c:491 [inline]
> BUG: KASAN: use-after-free in ucma_destroy_private_ctx+0x914/0xb70 drivers/infiniband/core/ucma.c:579
> Read of size 8 at addr ffff88801bb74b00 by task syz-executor.1/25529

Jason,

Can it be race between ucma_process_join() and "if (refcount_read(&ctx->ref))"
check in ucma_destroy_private_ctx()?

The ucma_process_join() grabbed ctx, but released it in error path,
while ucma_destroy_private_ctx() was called without holding any locks?

Thanks