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 Reported-by: Junrui Luo Fixes: b482cd2053e3 ("net-caif: add CAIF core protocol stack") Signed-off-by: Junrui Luo --- 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 6651a8dc62e0..d4d63586053a 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; --- base-commit: 559e608c46553c107dbba19dae0854af7b219400 change-id: 20251204-fixes-23393d72bfc8 Best regards, -- Junrui Luo