usb: gadget: f_phonet: fix skb frags[] overflow in pn_rx_complete()

A broken/bored/mean USB host can overflow the skb_shared_info->frags[]
array on a Linux gadget exposing a Phonet function by sending an
unbounded sequence of full-page OUT transfers.

pn_rx_complete() finalizes the skb only when req->actual < req->length,
where req->length is set to PAGE_SIZE by the gadget.  If the host always
sends exactly PAGE_SIZE bytes per transfer, fp->rx.skb will never be
reset and each completion will add another fragment via
skb_add_rx_frag().  Once nr_frags exceeds MAX_SKB_FRAGS (default 17),
subsequent frag stores overwrite memory adjacent to the shinfo on the
heap.

Drop the skb and account a length error when the frag limit is reached,
matching the fix applied in t7xx by commit f0813bcd2d9d ("net: wwan:
t7xx: fix potential skb->frags overflow in RX path").

Cc: stable <stable@kernel.org>
Assisted-by: gregkh_clanker_t1000
Link: https://patch.msgid.link/2026040705-fruit-unloved-0701@gregkh
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/usb/gadget/function/f_phonet.c b/drivers/usb/gadget/function/f_phonet.c
index 2c007790ead25a77614b939a73125e751f7e73b8..b1ee9a7c2e94401c5cfae4e3fad3ea727874a691 100644 (file)
--- a/drivers/usb/gadget/function/f_phonet.c
+++ b/drivers/usb/gadget/function/f_phonet.c
@@ -333,6 +333,15 @@ static void pn_rx_complete(struct usb_ep *ep, struct usb_request *req)
                if (unlikely(!skb))
                        break;
 
+               if (unlikely(skb_shinfo(skb)->nr_frags >= MAX_SKB_FRAGS)) {
+                       /* Frame count from host exceeds frags[] capacity */
+                       dev_kfree_skb_any(skb);
+                       if (fp->rx.skb == skb)
+                               fp->rx.skb = NULL;
+                       dev->stats.rx_length_errors++;
+                       break;
+               }
+
                if (skb->len == 0) { /* First fragment */
                        skb->protocol = htons(ETH_P_PHONET);
                        skb_reset_mac_header(skb);