[PATCH 5.10 28/84] ipv6: Fix signed integer overflow in l2tp_ip6_sendmsg

Greg Kroah-Hartman
2022-06-20T13:16:57Z

From: Wang Yufen <wangyufen@huawei.com>

[ Upstream commit f638a84afef3dfe10554c51820c16e39a278c915 ]

When len >= INT_MAX - transhdrlen, ulen = len + transhdrlen will be
overflow. To fix, we can follow what udpv6 does and subtract the
transhdrlen from the max.

Signed-off-by: Wang Yufen <wangyufen@huawei.com>
Link: https://lore.kernel.org/r/20220607120028.845916-2-wangyufen@huawei.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/l2tp/l2tp_ip6.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/l2tp/l2tp_ip6.c b/net/l2tp/l2tp_ip6.c
index 96f975777438..d54dbd01d86f 100644
--- a/net/l2tp/l2tp_ip6.c
+++ b/net/l2tp/l2tp_ip6.c
@@ -502,14 +502,15 @@ static int l2tp_ip6_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
struct ipcm6_cookie ipc6;
int addr_len = msg->msg_namelen;
int transhdrlen = 4; /* zero session-id */
- int ulen = len + transhdrlen;
+ int ulen;
int err;

/* Rough check on arithmetic overflow,
* better check is made in ip6_append_data().
*/
- if (len > INT_MAX)
+ if (len > INT_MAX - transhdrlen)
return -EMSGSIZE;
+ ulen = len + transhdrlen;

/* Mirror BSD error message compatibility */
if (msg->msg_flags & MSG_OOB)
--
2.35.1