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Bluetooth: L2CAP: validate connectionless PSM length

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Connectionless L2CAP frames carry a two-byte PSM at the start of the
payload.  l2cap_recv_frame() currently reads that PSM unconditionally
after validating only the outer L2CAP length.

A malformed connectionless frame with a zero- or one-byte payload can
therefore make the parser read beyond the advertised skb payload and use
tailroom bytes as part of the PSM.  A VHCI-backed QEMU reproducer
injected a one-byte connectionless payload and reached the unchecked
read.

Reject connectionless frames that cannot contain the PSM before reading
or pulling it.  This preserves all valid connectionless frames while
dropping only structurally incomplete packets.

Assisted-by: Codex:gpt-5.5-cyber-preview
Signed-off-by: Samuel Moelius <sam.moelius@trailofbits.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
This commit is contained in:
Samuel Moelius 2026-06-08 23:57:05 +00:00 committed by Luiz Augusto von Dentz
parent c38fbcdc40
commit a40a5f9225
1 changed files with 5 additions and 0 deletions
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5
net/bluetooth/l2cap_core.c
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@ -7029,6 +7029,11 @@ static void l2cap_recv_frame(struct l2cap_conn *conn, struct sk_buff *skb)
break;
case L2CAP_CID_CONN_LESS:
if (skb->len < L2CAP_PSMLEN_SIZE) {
kfree_skb(skb);
break;
}
psm = get_unaligned((__le16 *) skb->data);
skb_pull(skb, L2CAP_PSMLEN_SIZE);
l2cap_conless_channel(conn, psm, skb);