[PATCH 3.16 111/136] s390/cmm: fix information leak in cmm_timeout_handler()

Ben Hutchings
2019-12-17T00:54:14Z

From: Yihui ZENG <yzeng56@asu.edu>

commit b8e51a6a9db94bc1fb18ae831b3dab106b5a4b5f upstream.

The problem is that we were putting the NUL terminator too far:

buf[sizeof(buf) - 1] = '\0';

If the user input isn't NUL terminated and they haven't initialized the
whole buffer then it leads to an info leak. The NUL terminator should
be:

buf[len - 1] = '\0';

Signed-off-by: Yihui Zeng <yzeng56@asu.edu>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
[heiko.carstens@de.ibm.com: keep semantics of how *lenp and *ppos are handled]
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
arch/s390/mm/cmm.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

--- a/arch/s390/mm/cmm.c
+++ b/arch/s390/mm/cmm.c
@@ -306,16 +306,16 @@ static int cmm_timeout_handler(struct ct
}

if (write) {
- len = *lenp;
- if (copy_from_user(buf, buffer,
- len > sizeof(buf) ? sizeof(buf) : len))
+ len = min(*lenp, sizeof(buf));
+ if (copy_from_user(buf, buffer, len))
return -EFAULT;
- buf[sizeof(buf) - 1] = '\0';
+ buf[len - 1] = '\0';
cmm_skip_blanks(buf, &p);
nr = simple_strtoul(p, &p, 0);
cmm_skip_blanks(p, &p);
seconds = simple_strtoul(p, &p, 0);
cmm_set_timeout(nr, seconds);
+ *ppos += *lenp;
} else {
len = sprintf(buf, "%ld %ld\n",
cmm_timeout_pages, cmm_timeout_seconds);
@@ -323,9 +323,9 @@ static int cmm_timeout_handler(struct ct
len = *lenp;
if (copy_to_user(buffer, buf, len))
return -EFAULT;
+ *lenp = len;
+ *ppos += len;
}
- *lenp = len;
- *ppos += len;
return 0;
}