As skb->tail might be zero, it can underflow. This leads to a page
fault: skb_tail_pointer simply adds skb->tail (which is now MAX_UINT)
to skb->head.
BUG: unable to handle page fault for address: ffffed1021de29ff
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
RIP: 0010:rfcomm_run+0x831/0x4040 (net/bluetooth/rfcomm/core.c:1751)
By using skb_trim instead of the direct manipulation, skb->tail
is reset. Thus, the correct pointer to the checksum is used.
Signed-off-by: Soenke Huster <soenke.huster@xxxxxxxxx>
---
v2: Clarified how the bug triggers, minimize code change
net/bluetooth/rfcomm/core.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/bluetooth/rfcomm/core.c b/net/bluetooth/rfcomm/core.c
index 7324764384b6..443b55edb3ab 100644
--- a/net/bluetooth/rfcomm/core.c
+++ b/net/bluetooth/rfcomm/core.c
@@ -1747,7 +1747,7 @@ static struct rfcomm_session *rfcomm_recv_frame(struct rfcomm_session *s,
type = __get_type(hdr->ctrl);
/* Trim FCS */
- skb->len--; skb->tail--;
+ skb_trim(skb, skb->len - 1);
fcs = *(u8 *)skb_tail_pointer(skb);
if (__check_fcs(skb->data, type, fcs)) {
--
2.36.1
