Re: [PATCH] CIFS: fix use-after-free of the lease keys

[Paulo Alcantara <paulo@paulo.ac>]

Aurelien Aptel <aaptel@suse.com> writes:

> The request buffers are freed right before copying the pointers.
> Use the func args instead which are identical and still valid.
>
> Simple reproducer (requires KASAN enabled) on a cifs mount:
>
> echo foo > foo ; tail -f foo & rm foo
>
> Cc: <stable@vger.kernel.org> # 4.20
> Fixes: 179e44d49c2f ("smb3: add tracepoint for sending lease break responses to server")
> Signed-off-by: Aurelien Aptel <aaptel@suse.com>
> ---
>  fs/cifs/smb2pdu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
> index 846e605175bf..54181387a770 100644
> --- a/fs/cifs/smb2pdu.c
> +++ b/fs/cifs/smb2pdu.c
> @@ -4435,8 +4435,8 @@ SMB2_lease_break(const unsigned int xid, struct cifs_tcon *tcon,
>  	rc = cifs_send_recv(xid, ses, &rqst, &resp_buf_type, flags, &rsp_iov);
>  	cifs_small_buf_release(req);
>  
> -	please_key_low = (__u64 *)req->LeaseKey;
> -	please_key_high = (__u64 *)(req->LeaseKey+8);
> +	please_key_low = (__u64 *)lease_key;
> +	please_key_high = (__u64 *)(lease_key+8);
>  	if (rc) {
>  		cifs_stats_fail_inc(tcon, SMB2_OPLOCK_BREAK_HE);
>  		trace_smb3_lease_err(le32_to_cpu(lease_state), tcon->tid,
> -- 
> 2.16.4

Reviewed-by: Paulo Alcantara <palcantara@suse.de>

Thanks!
Paulo