[PATCH 4.9 38/59] fs/cifs: suppress a string overflow warning

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stephen Rothwell <s...@canb.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 <s...@canb.auug.org.au>
Signed-off-by: Steve French <stfre...@microsoft.com>
Signed-off-by: Sasha Levin <alexander.le...@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 fs/cifs/cifssmb.c |   11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -577,10 +577,15 @@ CIFSSMBNegotiate(const unsigned int xid,
        }
 
        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);