Re: potential null pointer dereference in drivers/isdn/hisax/isdnl2.c

From: Jesper Juhl <redacted>

quoted

In drivers/isdn/hisax/isdnl2.c:l2_pull_iqueue() we have this:

	...
		skb = alloc_skb(oskb->len + i, GFP_ATOMIC);
		memcpy(skb_put(skb, i), header, i);
	...

If alloc_skb() fails and returns NULL then the second line will cause a 
NULL pointer dereference - skb_put() gives the pointer to 
skb_tail_pointer() which dereferences it.

I'm not quite sure how this should be dealt with, so I'll just report it 
rather than submit a patch. Happy bug fixing :-)

Thanks Jesper, I'll fix this like so:

--------------------
hisax: Fix unchecked alloc_skb() return.

Jesper Juhl noticed that l2_pull_iqueue() does not
check to see if alloc_skb() fails.

Fix this by first trying to reallocate the headroom
if necessary, rather than later after we've made hard
to undo state changes.

Reported-by: Jesper Juhl <redacted>
Signed-off-by: David S. Miller <davem@davemloft.net>

---
drivers/isdn/hisax/isdnl2.c |   35 ++++++++++++++++++++---------------
 1 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/drivers/isdn/hisax/isdnl2.c b/drivers/isdn/hisax/isdnl2.c
index 0858791..98ac835 100644
--- a/drivers/isdn/hisax/isdnl2.c
+++ b/drivers/isdn/hisax/isdnl2.c

@@ -1243,14 +1243,21 @@ l2_st7_tout_203(struct FsmInst *fi, int event, void *arg)
 	st->l2.rc = 0;
 }
 
+static int l2_hdr_space_needed(struct Layer2 *l2)
+{
+	int len = test_bit(FLG_LAPD, &l2->flag) ? 2 : 1;
+
+	return len + (test_bit(FLG_LAPD, &l2->flag) ? 2 : 1);
+}
+