net/packet: check length in getsockopt() called with PACKET_HDRLEN

In the case getsockopt() is called with PACKET_HDRLEN and optlen < 4 |val| remains uninitialized and the syscall may behave differently depending on its value, and even copy garbage to userspace on certain architectures. To fix this we now return -EINVAL if optlen is too small. This bug has been detected with KMSAN. Signed-off-by: Alexander Potapenko <[email protected]> Signed-off-by: David S. Miller <[email protected]>
cail · Apr 25, 2017 · fd2c83b · fd2c83b
1 parent 8048ced
commit fd2c83b
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
@@ -3836,6 +3836,8 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
 	case PACKET_HDRLEN:
 		if (len > sizeof(int))
 			len = sizeof(int);
+		if (len < sizeof(int))
+			return -EINVAL;
 		if (copy_from_user(&val, optval, len))
 			return -EFAULT;
 		switch (val) {