Re: [PATCH for-v4.13 V4] brcmfmac: Don't grow SKB by negative size

[Kalle Valo]

Daniel Stone  writes:

> 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 
> Cc: Arend Van Spriel 
> Cc: James Hughes 
> Cc: Hante Meuleman 
> Cc: Pieter-Paul Giesberts 
> Cc: Franky Lin 

I'll queue this for 4.13.

-- 
Kalle Valo

[PATCH for-v4.13 V4] brcmfmac: Don't grow SKB by negative size

[Daniel Stone]

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 
Cc: Arend Van Spriel 
Cc: James Hughes 
Cc: Hante Meuleman 
Cc: Pieter-Paul Giesberts 
Cc: Franky Lin 
---
 drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

v2: Correct thinko.
v3: Bring assignment on to one line.
v4: Use max_t rather than max.

diff --git a/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c 
b/drivers/net/wireless/broadcom/brcm80211/brcmfmac/core.c
index 2153e8062b4c..5cc3a07dda9e 100644
--- 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);
-- 
2.13.2