[PATCH 6.18 135/198] usb: gadget: f_phonet: fix skb frags[] overflow in pn_rx_complete()

Greg Kroah-Hartman
2026-04-20T16:03:05Z

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

commit c088d5dd2fffb4de1fb8e7f57751c8b82942180a upstream.

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>
---
drivers/usb/gadget/function/f_phonet.c | 9 +++++++++
1 file changed, 9 insertions(+)

--- 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
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);