linux-kernel - [PATCH] cifs: cifssmb: Fix potential NULL pointer dereference

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Date:   Tue, 3 Apr 2018 15:55:12 -0500
From:   "Gustavo A. R. Silva" <garsilva@...eddedor.com>
To:     Ronnie Sahlberg <lsahlber@...hat.com>,
        Steve French <sfrench@...ba.org>
Cc:     linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>
Subject: [PATCH] cifs: cifssmb: Fix potential NULL pointer dereference

tcon->ses is being dereferenced before it is null checked, hence
there is a potential null pointer dereference.

Fix this by moving the pointer dereference after tcon->ses has
been properly null checked.

Addresses-Coverity-ID: 1467426 ("Dereference before null check")
Fixes: 93012bf98416 ("cifs: add server->vals->header_preamble_size")
Signed-off-by: Gustavo A. R. Silva <garsilva@...eddedor.com>
---
 fs/cifs/smb2pdu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index f7741ce..e5ac474 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -3454,7 +3454,7 @@ static int
 build_qfs_info_req(struct kvec *iov, struct cifs_tcon *tcon, int level,
 		   int outbuf_len, u64 persistent_fid, u64 volatile_fid)
 {
-	struct TCP_Server_Info *server = tcon->ses->server;
+	struct TCP_Server_Info *server;
 	int rc;
 	struct smb2_query_info_req *req;
 	unsigned int total_len;
@@ -3464,6 +3464,8 @@ build_qfs_info_req(struct kvec *iov, struct cifs_tcon *tcon, int level,
 	if ((tcon->ses == NULL) || (tcon->ses->server == NULL))
 		return -EIO;
 
+	server = tcon->ses->server;
+
 	rc = smb2_plain_req_init(SMB2_QUERY_INFO, tcon, (void **) &req,
 			     &total_len);
 	if (rc)
-- 
2.7.4