On 01/12/2014 10:39 AM, Bruce Liu wrote:
  When timestamping is enabled, stmmac_tx_clean will call 
stmmac_get_tx_hwtstamp to get tx TS.
  It's possible that skb is NULL because there are other network frames that 
use several descriptors.
  So we must return immediately in stmmac_get_tx_hwtstamp if skb is NULL to 
avoid system crash.


Signed-off-by: Bruce Liu <damuzi...@gmail.com>

Please see Documentation/SubmittingPatches +489

You subject line is way too long and should just be something like:

[PATCH net-next] net: stmmac: fix NULL pointer dereference in 
stmmac_get_tx_hwtstamp

Don't indent your actual commit message with whitespaces as prefix,
and do a line break after around 70 chars.

Btw, I mentioned net-next in the subject since merge window will
open soon anyway.

---
  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c |    2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c 
b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 797b56a..47f2287 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -332,7 +332,7 @@ static void stmmac_get_tx_hwtstamp(struct stmmac_priv *priv,
                return;

        /* exit if skb doesn't support hw tstamp */
-       if (likely(!(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS)))
+       if (likely(!skb || !(skb_shinfo(skb)->tx_flags & SKBTX_IN_PROGRESS)))
                return;

        if (priv->adv_ts)

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