[PATCH 6.12 057/567] caif: fix integer underflow in cffrml_receive()

Greg Kroah-Hartman
2026-01-06T17:17:25Z

From: Junrui Luo <moonafterrain@outlook.com>

[ Upstream commit 8a11ff0948b5ad09b71896b7ccc850625f9878d1 ]

The cffrml_receive() function extracts a length field from the packet
header and, when FCS is disabled, subtracts 2 from this length without
validating that len >= 2.

If an attacker sends a malicious packet with a length field of 0 or 1
to an interface with FCS disabled, the subtraction causes an integer
underflow.

This can lead to memory exhaustion and kernel instability, potential
information disclosure if padding contains uninitialized kernel memory.

Fix this by validating that len >= 2 before performing the subtraction.

Reported-by: Yuhao Jiang <danisjiang@gmail.com>
Reported-by: Junrui Luo <moonafterrain@outlook.com>
Fixes: b482cd2053e3 ("net-caif: add CAIF core protocol stack")
Signed-off-by: Junrui Luo <moonafterrain@outlook.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/SYBPR01MB7881511122BAFEA8212A1608AFA6A@SYBPR01MB7881.ausprd01.prod.outlook.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/caif/cffrml.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/net/caif/cffrml.c b/net/caif/cffrml.c
index 6651a8dc62e04..d4d63586053ad 100644
--- a/net/caif/cffrml.c
+++ b/net/caif/cffrml.c
@@ -92,8 +92,15 @@ static int cffrml_receive(struct cflayer *layr, struct cfpkt *pkt)
len = le16_to_cpu(tmp);

/* Subtract for FCS on length if FCS is not used. */
- if (!this->dofcs)
+ if (!this->dofcs) {
+ if (len < 2) {
+ ++cffrml_rcv_error;
+ pr_err("Invalid frame length (%d)\n", len);
+ cfpkt_destroy(pkt);
+ return -EPROTO;
+ }
len -= 2;
+ }

if (cfpkt_setlen(pkt, len) < 0) {
++cffrml_rcv_error;
--
2.51.0