linux-kernel - [PATCH][V2][cifs-next] cifs: fix dereference on ses before it is null checked

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Message-Id: <20190902151059.22088-1-colin.king@canonical.com>
Date:   Mon,  2 Sep 2019 16:10:59 +0100
From:   Colin King <colin.king@...onical.com>
To:     Steve French <sfrench@...ba.org>, linux-cifs@...r.kernel.org,
        samba-technical@...ts.samba.org
Cc:     kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH][V2][cifs-next] cifs: fix dereference on ses before it is null checked

From: Colin Ian King <colin.king@...onical.com>

The assignment of pointer server dereferences pointer ses, however,
this dereference occurs before ses is null checked and hence we
have a potential null pointer dereference.  Fix this by only
dereferencing ses after it has been null checked.

Addresses-Coverity: ("Dereference before null check")
Fixes: 2808c6639104 ("cifs: add new debugging macro cifs_server_dbg")
Signed-off-by: Colin Ian King <colin.king@...onical.com>
---
 fs/cifs/smb2pdu.c   | 11 ++++++++---
 fs/cifs/transport.c |  3 ++-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/cifs/smb2pdu.c b/fs/cifs/smb2pdu.c
index dbc6ef50dd45..0e92983de0b7 100644
--- a/fs/cifs/smb2pdu.c
+++ b/fs/cifs/smb2pdu.c
@@ -2759,8 +2759,10 @@ SMB2_ioctl(const unsigned int xid, struct cifs_tcon *tcon, u64 persistent_fid,
 	else
 		return -EIO;
 
+	if (!ses)
+		return -EIO;
 	server = ses->server;
-	if (!ses || !(server))
+	if (!server)
 		return -EIO;
 
 	if (smb3_encryption_required(tcon))
@@ -3058,13 +3060,16 @@ query_info(const unsigned int xid, struct cifs_tcon *tcon,
 	int rc = 0;
 	int resp_buftype = CIFS_NO_BUFFER;
 	struct cifs_ses *ses = tcon->ses;
-	struct TCP_Server_Info *server = ses->server;
+	struct TCP_Server_Info *server;
 	int flags = 0;
 	bool allocated = false;
 
 	cifs_dbg(FYI, "Query Info\n");
 
-	if (!ses || !(server))
+	if (!ses)
+		return -EIO;
+	server = ses->server;
+	if (!server)
 		return -EIO;
 
 	if (smb3_encryption_required(tcon))
diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c
index 0d60bd2f4dca..a90bd4d75b4d 100644
--- a/fs/cifs/transport.c
+++ b/fs/cifs/transport.c
@@ -1242,12 +1242,13 @@ SendReceive(const unsigned int xid, struct cifs_ses *ses,
 	struct kvec iov = { .iov_base = in_buf, .iov_len = len };
 	struct smb_rqst rqst = { .rq_iov = &iov, .rq_nvec = 1 };
 	struct cifs_credits credits = { .value = 1, .instance = 0 };
-	struct TCP_Server_Info *server = ses->server;
+	struct TCP_Server_Info *server;
 
 	if (ses == NULL) {
 		cifs_dbg(VFS, "Null smb session\n");
 		return -EIO;
 	}
+	server = ses->server;
 	if (server == NULL) {
 		cifs_dbg(VFS, "Null tcp session\n");
 		return -EIO;
-- 
2.20.1