caif: fix integer underflow in cffrml_receive()

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>

diff --git a/net/caif/cffrml.c b/net/caif/cffrml.c
index 6651a8dc62e04dba7de282f6d651d950ee22c367..d4d63586053ad4b1cb4cdab98af7ac6500b411f7 100644 (file)
--- 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;