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s390/cmm: fix information leak in cmm_timeout_handler()

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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>
Cc: stable@vger.kernel.org
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>
This commit is contained in:
Yihui ZENG 2019-10-25 12:31:48 +03:00 committed by Vasily Gorbik
parent d6d5df1db6
commit b8e51a6a9d
1 changed files with 6 additions and 6 deletions
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12
arch/s390/mm/cmm.c
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@ -298,16 +298,16 @@ static int cmm_timeout_handler(struct ctl_table *ctl, int write,
}
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);
@ -315,9 +315,9 @@ static int cmm_timeout_handler(struct ctl_table *ctl, int write,
len = *lenp;
if (copy_to_user(buffer, buf, len))
return -EFAULT;
*lenp = len;
*ppos += len;
}
*lenp = len;
*ppos += len;
return 0;
}