linux-kernel - Re: [PATCH] cifs: fix memory leak of an allocated cifs

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Date:   Tue, 8 Jan 2019 12:42:49 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Colin King <colin.king@...onical.com>
Cc:     Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cifs: fix memory leak of an allocated cifs_ntsd structure

On Mon, Jan 07, 2019 at 05:15:15PM +0000, Colin King wrote:
> From: Colin Ian King <colin.king@...onical.com>
> 
> The call to SMB2_queary_acl can allocate memory to pntsd and also
> return a failure via a call to SMB2_query_acl (and then query_info).
> This occurs when query_info allocates the structure and then in
> query_info the call to smb2_validate_and_copy_iov fails. Currently the
> failure just returns without kfree'ing pntsd hence causing a memory
> leak.  Fix this by kfree'ing pntsd before returning.
> 
> Detected by CoverityScan, CID#1457059 ("Resource Leak")
> 
> Fixes: 2f1afe25997f ("cifs: Use smb 2 - 3 and cifsacl mount options getacl functions")
> Signed-off-by: Colin Ian King <colin.king@...onical.com>
> ---
>  fs/cifs/smb2ops.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
> index cf7eb891804f..6d71958ad2cb 100644
> --- a/fs/cifs/smb2ops.c
> +++ b/fs/cifs/smb2ops.c
> @@ -2238,8 +2238,10 @@ get_smb2_acl_by_fid(struct cifs_sb_info *cifs_sb,
>  	cifs_put_tlink(tlink);
>  
>  	cifs_dbg(FYI, "%s: rc = %d ACL len %d\n", __func__, rc, *pacllen);
> -	if (rc)
> +	if (rc) {
> +		kfree(pntsd);
>  		return ERR_PTR(rc);
> +	}

This is a layering violation.  The memory was allocated in query_info()
so it should be freed there instead.  Also if the kmalloc() fails in
query_info() then it should return -ENOMEM instead of success.

This only affects code which calls SMB2_query_acl().  There are two
callers.  You have fixed one but the other is also buggy because we're
returning uninitialized memory in get_smb2_acl_by_path().

regards,
dan carpenter