linux-kernel - Re: [PATCH 2/3] ceph: fix use-after-free in ceph

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Date:   Fri, 04 Mar 2022 13:20:31 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     Luís Henriques <lhenriques@...e.de>,
        Xiubo Li <xiubli@...hat.com>, Ilya Dryomov <idryomov@...il.com>
Cc:     ceph-devel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

On Fri, 2022-03-04 at 16:14 +0000, Luís Henriques wrote:
> After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
> should be set to NULL, otherwise we may end-up freeing it twince and get
> the following splat:
> 
>   refcount_t: underflow; use-after-free.
>   WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
>   ...
>   Call Trace:
>     <TASK>
>     ceph_readdir+0xd35/0x1460 [ceph]
>     ? _raw_spin_unlock+0x12/0x30
>     ? preempt_count_add+0x73/0xa0
>     ? _raw_spin_unlock+0x12/0x30
>     ? __mark_inode_dirty+0x27c/0x3a0
>     iterate_dir+0x7d/0x190
>     __x64_sys_getdents64+0x80/0x120
>     ? compat_fillonedir+0x160/0x160
>     do_syscall_64+0x43/0x90
>     entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Signed-off-by: Luís Henriques <lhenriques@...e.de>
> ---
>  fs/ceph/dir.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
> index 0bcb677d2199..934402f5e9e6 100644
> --- a/fs/ceph/dir.c
> +++ b/fs/ceph/dir.c
> @@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
>  			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
>  			dout("filldir stopping us...\n");
>  			ceph_mdsc_put_request(dfi->last_readdir);
> +			dfi->last_readdir = NULL;
>  			err = 0;
>  			goto out;
>  		}

I think Xiubo fixed this in the testing branch late yesterday. It should
no longer be needed.

Thanks,
-- 
Jeff Layton <jlayton@...nel.org>