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From: Dan Carpenter <dan.carpenter@oracle.com>
To: Andrew Morton <akpm@linux-foundation.org>,
	Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	syzbot <syzbot+e64a13c5369a194d67df@syzkaller.appspotmail.com>,
	aarcange@redhat.com, hughd@google.com, mhocko@suse.com,
	syzkaller-bugs@googlegroups.com, vbabka@suse.cz,
	viro@zeniv.linux.org.uk, yang.shi@linux.alibaba.com
Subject: [PATCH] mm/mempolicy.c: Fix out of bounds write in mpol_parse_str()
Date: Wed, 15 Jan 2020 08:54:26 +0300
Message-ID: <20200115055426.vdjwvry44nfug7yy@kili.mountain> (raw)
In-Reply-To: <0000000000006a8b8f059c24672a@google.com>

What we are trying to do is change the '=' character to a NUL terminator
and then at the end of the function we restore it back to an '='.  The
problem is there are two error paths where we jump to the end of the
function before we have replaced the '=' with NUL.  We end up putting
the '=' in the wrong place (possibly one element before the start of
the buffer).

Reported-by: syzbot+e64a13c5369a194d67df@syzkaller.appspotmail.com
Fixes: 095f1fc4ebf3 ("mempolicy: rework shmem mpol parsing and display")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
 mm/mempolicy.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 067cf7d3daf5..1340c5c496b5 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -2817,6 +2817,9 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 	char *flags = strchr(str, '=');
 	int err = 1, mode;
 
+	if (flags)
+		*flags++ = '\0';	/* terminate mode string */
+
 	if (nodelist) {
 		/* NUL-terminate mode or flags string */
 		*nodelist++ = '\0';
@@ -2827,9 +2830,6 @@ int mpol_parse_str(char *str, struct mempolicy **mpol)
 	} else
 		nodes_clear(nodes);
 
-	if (flags)
-		*flags++ = '\0';	/* terminate mode string */
-
 	mode = match_string(policy_modes, MPOL_MAX, str);
 	if (mode < 0)
 		goto out;
-- 
2.11.0



  reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-15  2:24 KASAN: slab-out-of-bounds Write in mpol_parse_str syzbot
2020-01-15  5:54 ` Dan Carpenter [this message]
2020-01-15 12:54   ` [PATCH] mm/mempolicy.c: Fix out of bounds write in mpol_parse_str() Vlastimil Babka
2020-01-15 12:57     ` Dmitry Vyukov
2020-01-15 15:03       ` Michal Hocko
2020-01-15 15:14         ` Dmitry Vyukov
2020-01-15 19:05           ` Michal Hocko
2020-01-16  5:41             ` Dmitry Vyukov
2020-01-16  7:39               ` Michal Hocko
2020-01-16 10:13                 ` Dmitry Vyukov
2020-01-16 11:51                   ` Michal Hocko
2020-01-16 12:41                     ` Dmitry Vyukov
2020-01-16 14:05                       ` Michal Hocko

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