Bluetooth: RFCOMM: validate skb length in rfcomm_recv_frame

rfcomm_recv_frame() casts skb->data to struct rfcomm_hdr and dereferences
hdr->addr and hdr->ctrl without validating skb->len first. A truncated
frame with skb->len less than the minimum header size causes an
out-of-bounds read of uninitialized memory. Additionally, a zero-length
frame causes skb->len-- to underflow to UINT_MAX, making
skb_tail_pointer() read far past the buffer.

Commit 23882b828c3c ("Bluetooth: RFCOMM: validate skb length in MCC
handlers") fixed the same class of missing-length-check bugs in the MCC
sub-handlers, but the top-level rfcomm_recv_frame() was left unfixed.
KMSAN reports:

  BUG: KMSAN: uninit-value in rfcomm_run
  ...
  Uninit was created at:
    __alloc_skb+0x474/0xb60
    vhci_write+0xe9/0x870

Fix this by rejecting frames smaller than sizeof(struct rfcomm_hdr) + 1
(the minimum frame must have a 3-byte header and a 1-byte FCS).

Signed-off-by: Jiale Yao <yaojiale02@163.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 75f7512dec54285e39f26488ac7be966e8b0df87..2e8c080b4d9ebaa450a280b820291ff6c0b7a3fa 100644 (file)
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1795,6 +1795,11 @@ static struct rfcomm_session *rfcomm_recv_frame(struct rfcomm_session *s,
                return s;
        }
 
+       if (skb->len < sizeof(*hdr) + 1) {
+               kfree_skb(skb);
+               return s;
+       }
+
        dlci = __get_dlci(hdr->addr);
        type = __get_type(hdr->ctrl);