linux-kernel - [PATCH AUTOSEL 4.9 30/57] s390/extmem: fix gcc 8 stringop-overflow warning

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Message-ID: <20180917030340.378-30-alexander.levin@microsoft.com>
Date:   Mon, 17 Sep 2018 03:04:01 +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:     Vasily Gorbik <gor@...ux.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.9 30/57] s390/extmem: fix gcc 8 stringop-overflow
 warning

From: Vasily Gorbik <gor@...ux.ibm.com>

[ Upstream commit 6b2ddf33baec23dace85bd647e3fc4ac070963e8 ]

arch/s390/mm/extmem.c: In function '__segment_load':
arch/s390/mm/extmem.c:436:2: warning: 'strncat' specified bound 7 equals
source length [-Wstringop-overflow=]
  strncat(seg->res_name, " (DCSS)", 7);

What gcc complains about here is the misuse of strncat function, which
in this case does not limit a number of bytes taken from "src", so it is
in the end the same as strcat(seg->res_name, " (DCSS)");

Keeping in mind that a res_name is 15 bytes, strncat in this case
would overflow the buffer and write 0 into alignment byte between the
fields in the struct. To avoid that increasing res_name size to 16,
and reusing strlcat.

Reviewed-by: Heiko Carstens <heiko.carstens@...ibm.com>
Signed-off-by: Vasily Gorbik <gor@...ux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@...ibm.com>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 arch/s390/mm/extmem.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/s390/mm/extmem.c b/arch/s390/mm/extmem.c
index 02042b6b66bf..e6665a6e105e 100644
--- a/arch/s390/mm/extmem.c
+++ b/arch/s390/mm/extmem.c
@@ -79,7 +79,7 @@ struct qin64 {
 struct dcss_segment {
 	struct list_head list;
 	char dcss_name[8];
-	char res_name[15];
+	char res_name[16];
 	unsigned long start_addr;
 	unsigned long end;
 	atomic_t ref_count;
@@ -432,7 +432,7 @@ __segment_load (char *name, int do_nonshared, unsigned long *addr, unsigned long
 	memcpy(&seg->res_name, seg->dcss_name, 8);
 	EBCASC(seg->res_name, 8);
 	seg->res_name[8] = '\0';
-	strncat(seg->res_name, " (DCSS)", 7);
+	strlcat(seg->res_name, " (DCSS)", sizeof(seg->res_name));
 	seg->res->name = seg->res_name;
 	rc = seg->vm_segtype;
 	if (rc == SEG_TYPE_SC ||
-- 
2.17.1