linux-kernel - Re: [PATCH] xfs: fix potential memory leak in xfs_bmap_add

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Date:   Wed, 6 Jul 2022 10:24:43 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Jianglei Nie <niejianglei2021@....com>
Cc:     dchinner@...hat.com, chandan.babu@...cle.com,
        linux-xfs@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xfs: fix potential memory leak in xfs_bmap_add_attrfork()

On Wed, Jul 06, 2022 at 04:22:37PM +0800, Jianglei Nie wrote:
> xfs_bmap_add_attrfork() allocates a memory chunk for ip->i_afp with
> xfs_ifork_alloc(). When some error occurs, the function goto trans_cancel;
> without releasing the ip->i_afp, which will lead to a memory leak.
> 
> We should release the ip->i_afp with kmem_cache_free() and set "ip->i_afp
> = NULL" if ip->i_afp is not NULL pointer.
> 
> Signed-off-by: Jianglei Nie <niejianglei2021@....com>
> ---
>  fs/xfs/libxfs/xfs_bmap.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index 6833110d1bd4..0c99726c0968 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -1088,6 +1088,10 @@ xfs_bmap_add_attrfork(
>  trans_cancel:
>  	xfs_trans_cancel(tp);
>  	xfs_iunlock(ip, XFS_ILOCK_EXCL);
> +	if (ip->i_afp) {
> +		kmem_cache_free(xfs_ifork_cache, ip->i_afp);
> +		ip->a_afp = NULL;
> +	}

I don't think this is correct.  If xfs_bmap_add_attrfork_* fail without
dirtying the transaction, this function cancels the transaction without
shutting down the filesystem, and return the error code to the caller.
However, i_forkoff is not reset to zero, which means that the inode
still has an attr fork, so i_afp must not be freed.

Freeing the memory and nulling out the pointer without resetting
i_forkoff results in inconsistent incore state, which will probably lead
to a crash somewhere.  In the end, inode reclaim will free i_afp.

I think this is mooted by[1], right?

--D

[1] https://lore.kernel.org/linux-xfs/165705898555.2826746.14913566803667615290.stgit@magnolia/T/#u

>  	return error;
>  }
>  
> -- 
> 2.25.1
>