[PATCH] Bluetooth: RFCOMM: validate skb length in rfcomm_recv_frame

[PATCH] Bluetooth: RFCOMM: validate skb length in rfcomm_recv_frame

[Jiale Yao]

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>
---
 net/bluetooth/rfcomm/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index ebeae17b71d1..37c23ef47baf 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1778,6 +1778,11 @@ 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);
 
-- 
2.34.1

Re: [PATCH] Bluetooth: RFCOMM: validate skb length in rfcomm_recv_frame

[patchwork-bot+bluetooth]

Hello:

This patch was applied to bluetooth/bluetooth-next.git (master)
by Luiz Augusto von Dentz <luiz.von.dentz@intel.com>:

On Wed, 22 Jul 2026 17:26:14 +0800 you wrote:
> 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.
> 
> [...]

Here is the summary with links:
  - Bluetooth: RFCOMM: validate skb length in rfcomm_recv_frame
    https://git.kernel.org/bluetooth/bluetooth-next/c/4c7de7083a9a

You are awesome, thank you!
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