brcmfmac: Don't grow SKB by negative size

The commit to rework the headroom check in start_xmit() now calls
pxskb_expand_head() unconditionally if the header is CoW. Unfortunately,
it does so with the delta between the extant headroom and the header
length, which may be negative if there is already sufficient headroom.

pskb_expand_head() does allow for size being 0, in which case it just
copies, so clamp the header delta to zero.

Opening Chrome (and all my tabs) on a PCIE device was enough to reliably
hit this.

Fixes: 270a6c1f65fe ("brcmfmac: rework headroom check in .start_xmit()")
Signed-off-by: Daniel Stone <daniels@collabora.com>
Cc: Arend Van Spriel <arend.vanspriel@broadcom.com>
Cc: James Hughes <james.hughes@raspberrypi.org>
Cc: Hante Meuleman <hante.meuleman@broadcom.com>
Cc: Pieter-Paul Giesberts <pieter-paul.giesberts@broadcom.com>
Cc: Franky Lin <franky.lin@broadcom.com>
Tested-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
index 2153e8062b4cefcca2ee92c6459fae295fbf4500..5cc3a07dda9e6acf202ba29a1f0a420814c4a96d 100644 (file)
--- a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
+++ b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
@@ -214,7 +214,7 @@ static netdev_tx_t brcmf_netdev_start_xmit(struct sk_buff *skb,
 
        /* Make sure there's enough writeable headroom */
        if (skb_headroom(skb) < drvr->hdrlen || skb_header_cloned(skb)) {
-               head_delta = drvr->hdrlen - skb_headroom(skb);
+               head_delta = max_t(int, drvr->hdrlen - skb_headroom(skb), 0);
 
                brcmf_dbg(INFO, "%s: insufficient headroom (%d)\n",
                          brcmf_ifname(ifp), head_delta);