On 09/02/2015 01:35 PM, Ken-ichirou MATSUZAWA wrote:
Thank you for the reply.
On Wed, Sep 02, 2015 at 11:47:26AM +0200, Daniel Borkmann wrote:
On 09/02/2015 02:04 AM, Ken-ichirou MATSUZAWA wrote:
Talking about skb_copy path, original skb's shared info is accessed
only in copy_skb_header, to get gso related field. As a result of
It's still not correct. The thing is you can neither call skb_copy() nor
skb_clone() on netlink mmaped skbs. For example, skb_copy_bits() would
I am sorry for the lack of explanation.
And I am afraid I misunderstand...
Updated pointers to its data area in a mmaped netlink skb is only
its tail. Head, data and end will not be updated. skb_copy() calls
int skb_copy_bits(const struct sk_buff *skb, int offset, void *to, int len)
as its argument, "offset" is always 0 and "len" is skb->len. In
skb_copy_bits() both "start" and "copy" are skb->len, which means
"len - copy" is always 0 so that retuns 0 before accessing shared
info.
I don't know the situation is intended or not, it seems that
skb_copy() for a mmaped skb will not access its shared info.
Okay, right, since it's all linear, but ...
After that, copy_skb_header() will set newly allocate skb's (wrong)
gso fields, I asked we should clear it or not.
... here still we access skb_shinfo() from the mmap'ed skb, which we
are simply not allowed (despite whether resetting fields later on as
you suggest or not), for two reasons: I think (will start experimenting
more with it tomorrow), you would get an out of bounds access here in
case the skb->data is the last slot in the ring buffer and reaches
exactly to the ring buffer end. And (despite that), it's also hard
to maintain - the next one adding a new shared info member will very
likely oversee this special case in netlink here, thus the issue would
then simply be reintroduced over and over.
Thanks,
Daniel
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