From ec13df6442492592eb6a0b21d65d0489ac91a180 Mon Sep 17 00:00:00 2001
From: Yihui ZENG yzeng56@asu.edu Date: Fri, 25 Oct 2019 12:31:48 +0300 Subject: [PATCH] s390/cmm: fix information leak in cmm_timeout_handler()
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 (cherry picked from commit b8e51a6a9db94bc1fb18ae831b3dab106b5a4b5f) Signed-off-by: Nico Pache npache@redhat.com --- arch/s390/mm/cmm.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/arch/s390/mm/cmm.c b/arch/s390/mm/cmm.c index 9d84a1feefef..846561d4245e 100644 --- a/arch/s390/mm/cmm.c +++ b/arch/s390/mm/cmm.c @@ -306,16 +306,16 @@ static int cmm_timeout_handler(ctl_table *ctl, int write, void __user *buffer, }
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(ctl_table *ctl, int write, void __user *buffer, len = *lenp; if (copy_to_user(buffer, buf, len)) return -EFAULT; + *lenp = len; + *ppos += len; } - *lenp = len; - *ppos += len; return 0; }