Re: mac80211 truesize bugs

Johannes Berg
2008-05-03T22:56:38Z

On Sat, 2008-05-03 at 18:03 +0200, Johannes Berg wrote:
> On Sat, 2008-05-03 at 20:59 +0800, Herbert Xu wrote:
> > On Sat, May 03, 2008 at 02:38:01PM +0200, Johannes Berg wrote:
> > >
> > > Why, btw? It's not too hard to check the allocated size, no?
> >=20
> > Yes that would be a meaningful improvement although we'd need to
> > audit/test this to make sure that we don't spam people's logs
> > with it.
>=20
> It does spam the log. A lot. And I don't know why, from this discussi=
on
> I only thought that it shouldn't.

This was a stupid mistake, if you do it correctly it actually works and
so far has only triggered a single warning on my system:

[ 217.507048] SKB BUG: Invalid truesize (4294964120) size=3D432, sizeo=
f(sk_buff)=3D176
=EF=BB=BF
that was with my patch though to update skb->truesize during !skb->sk
pskb_expand_head() calls.

johannes

---
include/linux/skbuff.h | 8 ++++++--
net/core/skbuff.c | 10 ++++++++--
2 files changed, 14 insertions(+), 4 deletions(-)

--- everything.orig/include/linux/skbuff.h 2008-05-03 15:47:00.00000000=
0 +0200
+++ everything/include/linux/skbuff.h 2008-05-04 00:30:34.000000000 +02=
00
@@ -387,9 +387,13 @@ extern void skb_truesize_bug(struc
=20
static inline void skb_truesize_check(struct sk_buff *skb)
{
- int len =3D sizeof(struct sk_buff) + skb->len;
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+ int len =3D sizeof(struct sk_buff) + skb->end;
+#else
+ int len =3D sizeof(struct sk_buff) + (skb->end - skb->head);
+#endif
=20
- if (unlikely((int)skb->truesize < len))
+ if (unlikely((int)skb->truesize !=3D len))
skb_truesize_bug(skb);
}
=20
--- everything.orig/net/core/skbuff.c 2008-05-03 16:29:23.000000000 +02=
00
+++ everything/net/core/skbuff.c 2008-05-04 00:31:32.000000000 +0200
@@ -151,9 +151,15 @@ void skb_under_panic(struct sk_buff *skb
=20
void skb_truesize_bug(struct sk_buff *skb)
{
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+ int len =3D sizeof(struct sk_buff) + skb->end;
+#else
+ int len =3D sizeof(struct sk_buff) + (skb->end - skb->head);
+#endif
+
printk(KERN_ERR "SKB BUG: Invalid truesize (%u) "
- "len=3D%u, sizeof(sk_buff)=3D%Zd\n",
- skb->truesize, skb->len, sizeof(struct sk_buff));
+ "size=3D%u, sizeof(sk_buff)=3D%Zd\n",
+ skb->truesize, len, sizeof(struct sk_buff));
}
EXPORT_SYMBOL(skb_truesize_bug);
=20

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