[PATCH net-next v2 4/7] phonet: pep: do not write beyond optlen in getsockopt

[Breno Leitao <leitao@debian.org>]

pep_getsockopt() clamps the reported length to the caller's buffer with
min_t(), but then stores the value with put_user(val, (int __user *)
optval), which always writes sizeof(int) bytes. A getsockopt() call with
an optlen smaller than sizeof(int) thus reports the clamped length yet
writes a full int, one to three bytes past the user buffer.

Write the value with copy_to_user() bounded by len, so at most optlen
bytes are copied, matching the length reported back to userspace.

Fixes: 02a47617cdce ("Phonet: implement GPRS virtual interface over PEP socket")
Signed-off-by: Breno Leitao <leitao@debian.org>
Acked-by: Rémi Denis-Courmont <remi@remlab.net>
---
 net/phonet/pep.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/phonet/pep.c b/net/phonet/pep.c
index 7069271393933..60d1a5375725b 100644
--- a/net/phonet/pep.c
+++ b/net/phonet/pep.c
@@ -1115,7 +1115,7 @@ static int pep_getsockopt(struct sock *sk, int level, int optname,
 	len = min_t(unsigned int, sizeof(int), len);
 	if (put_user(len, optlen))
 		return -EFAULT;
-	if (put_user(val, (int __user *) optval))
+	if (copy_to_user(optval, &val, len))
 		return -EFAULT;
 	return 0;
 }

-- 
2.53.0-Meta