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A remote device can send a crafted UIH frame with a one-byte or zero-byte MCC payload to trigger an out-of-bounds read of the second byte. The unconditional skb_pull(skb, 2) that follows compounds the problem: if skb->len is less than 2, skb->data and skb->len are corrupted for all downstream MCC sub-handlers. Replace the open-coded cast and skb_pull() with skb_pull_data(), which atomically validates skb->len against sizeof(*mcc) and advances skb->data. Return -EILSEQ on failure. SeungJu Cheon's v2 patch added a manual skb->len size check in rfcomm_recv_mcc() before an open-coded cast, but removed the subsequent skb_pull(skb, 2) without replacing it. This leaves skb->data pointing at the MCC header when the sub-handlers are called, causing them to parse from the wrong offset. Using skb_pull_data() here avoids this problem: it validates, casts, and advances skb->data atomically, and is consistent with how the sub-handlers themselves were fixed in Cheon's patch. Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Link: https://lore.kernel.org/linux-bluetooth/20260414010741.233892-1-suunj1331@gmail.com/ Signed-off-by: Muhammad Bilal --- net/bluetooth/rfcomm/core.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c index d11bd5337..4e8047012 100644 --- a/net/bluetooth/rfcomm/core.c +++ b/net/bluetooth/rfcomm/core.c @@ -1644,17 +1644,20 @@ static int rfcomm_recv_msc(struct rfcomm_session *s, int cr, struct sk_buff *skb static int rfcomm_recv_mcc(struct rfcomm_session *s, struct sk_buff *skb) { - struct rfcomm_mcc *mcc = (void *) skb->data; + struct rfcomm_mcc *mcc; u8 type, cr, len; + /* Minimum MCC frame: type(1) + len(1) */ + mcc = skb_pull_data(skb, sizeof(*mcc)); + if (!mcc) + return -EILSEQ; + cr = __test_cr(mcc->type); type = __get_mcc_type(mcc->type); len = __get_mcc_len(mcc->len); BT_DBG("%p type 0x%x cr %d", s, type, cr); - skb_pull(skb, 2); - switch (type) { case RFCOMM_PN: rfcomm_recv_pn(s, cr, skb); -- 2.54.0