Re: [syzbot] [net?] kernel BUG in set_ipsecrequest

[shaurya <ssranevjti@gmail.com>]

#syz test: 
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


 From 123c5ac9ba261681b58a6217409c94722fde4249 Mon Sep 17 00:00:00 2001
From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Date: Sun, 19 Oct 2025 23:18:30 +0530
Subject: [PATCH] net: key: Validate address family in set_ipsecrequest()

syzbot reported a kernel BUG in set_ipsecrequest() due to an
skb_over_panic when processing XFRM_MSG_MIGRATE messages.

The root cause is that set_ipsecrequest() does not validate the
address family parameter before using it to calculate buffer sizes.
When an unsupported family value (such as 0) is passed,
pfkey_sockaddr_len() returns 0, leading to incorrect size calculations.

In pfkey_send_migrate(), the buffer size is calculated based on
pfkey_sockaddr_pair_size(), which uses pfkey_sockaddr_len(). When
family=0, this returns 0, so only sizeof(struct sadb_x_ipsecrequest)
(16 bytes) is allocated per entry. However, set_ipsecrequest() is
called multiple times in a loop (once for old_family, once for
new_family, for each migration bundle), repeatedly calling skb_put_zero()
with 16 bytes each time.

This causes the tail pointer to exceed the end pointer of the skb,
triggering skb_over_panic:
   tail: 0x188 (392 bytes)
   end:  0x180 (384 bytes)

Fix this by validating that pfkey_sockaddr_len() returns a non-zero
value before proceeding with buffer operations. This ensures proper
size calculations and prevents buffer overflow. Checking socklen
instead of just family==0 provides comprehensive validation for all
unsupported address families.

Reported-by: syzbot+be97dd4da14ae88b6ba4@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=be97dd4da14ae88b6ba4
Fixes: 08de61beab8a ("[PFKEYV2]: Extension for dynamic update of 
endpoint address(es)")

Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
  net/key/af_key.c | 4 ++++
  1 file changed, 4 insertions(+)

diff --git a/net/key/af_key.c b/net/key/af_key.c
index 2ebde0352245..713344c594d4 100644
--- a/net/key/af_key.c
+++ b/net/key/af_key.c
@@ -3526,6 +3526,10 @@ static int set_ipsecrequest(struct sk_buff *skb,
      int socklen = pfkey_sockaddr_len(family);
      int size_req;

+    /* Reject invalid/unsupported address families */
+    if (!socklen)
+        return -EINVAL;
+
      size_req = sizeof(struct sadb_x_ipsecrequest) +
             pfkey_sockaddr_pair_size(family);

-- 
2.34.1