linux-kernel - [PATCH] fs/cifs: suppress a string overflow warning

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Date:   Mon, 3 Sep 2018 13:15:58 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     Steve French <sfrench@...ba.org>
Cc:     linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        Linux-kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] fs/cifs: suppress a string overflow warning

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>
---
 fs/cifs/cifssmb.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifssmb.c b/fs/cifs/cifssmb.c
index dc2f4cf08fe9..dcf939cb9d2f 100644
--- a/fs/cifs/cifssmb.c
+++ b/fs/cifs/cifssmb.c
@@ -601,10 +601,14 @@ 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);
-- 
2.19.0.rc1

-- 
Cheers,
Stephen Rothwell

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