linux-kernel - [PATCH AUTOSEL 4.4 07/17] fs/cifs: suppress a string overflow warning

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Date:   Mon, 1 Oct 2018 00:41:29 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Stephen Rothwell <sfr@...b.auug.org.au>,
        Steven French <Steven.French@...rosoft.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.4 07/17] fs/cifs: suppress a string overflow warning

From: Stephen Rothwell <sfr@...b.auug.org.au>

[ Upstream commit bcfb84a996f6fa90b5e6e2954b2accb7a4711097 ]

A powerpc build of cifs with gcc v8.2.0 produces this warning:

fs/cifs/cifssmb.c: In function ‘CIFSSMBNegotiate’:
fs/cifs/cifssmb.c:605:3: warning: ‘strncpy’ writing 16 bytes into a region of size 1 overflows the destination [-Wstringop-overflow=]
   strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Since we are already doing a strlen() on the source, change the strncpy
to a memcpy().

Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
Signed-off-by: Steve French <stfrench@...rosoft.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 fs/cifs/cifssmb.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index 63aea21e6298..b9b8f19dce0e 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -577,10 +577,15 @@ CIFSSMBNegotiate(const unsigned int xid, struct cifs_ses *ses)
 	}
 
 	count = 0;
+	/*
+	 * We know that all the name entries in the protocols array
+	 * are short (< 16 bytes anyway) and are NUL terminated.
+	 */
 	for (i = 0; i < CIFS_NUM_PROT; i++) {
-		strncpy(pSMB->DialectsArray+count, protocols[i].name, 16);
-		count += strlen(protocols[i].name) + 1;
-		/* null at end of source and target buffers anyway */
+		size_t len = strlen(protocols[i].name) + 1;
+
+		memcpy(pSMB->DialectsArray+count, protocols[i].name, len);
+		count += len;
 	}
 	inc_rfc1001_len(pSMB, count);
 	pSMB->ByteCount = cpu_to_le16(count);
-- 
2.17.1