[linux-2.6] Fix signedness issues in net/core/filter.c

[Florian Weimer <fw@deneb.enyo.de>]

Is the issue described below already on your radar screen?  I couldn't
find it in the relevant files.  AFAICT, no CVE name has been assigned.

commit 4717ecd49ce5c556d38e8c7b6fdc9fac5d35c00e
Author: Patrick McHardy <kaber@trash.net>
Date:   Mon Jul 18 06:52:50 2005 +0200

    [PATCH] Fix signedness issues in net/core/filter.c
    
    This is the code to load packet data into a register:
    
                            k = fentry->k;
                            if (k < 0) {
    ...
                            } else {
                                    u32 _tmp, *p;
                                    p = skb_header_pointer(skb, k, 4, &_tmp);
                                    if (p != NULL) {
                                            A = ntohl(*p);
                                            continue;
                                    }
                            }
    
    skb_header_pointer checks if the requested data is within the
    linear area:
    
            int hlen = skb_headlen(skb);
    
            if (offset + len <= hlen)
                    return skb->data + offset;
    
    When offset is within [INT_MAX-len+1..INT_MAX] the addition will
    result in a negative number which is <= hlen.
    
    I couldn't trigger a crash on my AMD64 with 2GB of memory, but a
    coworker tried on his x86 machine and it crashed immediately.
    
    This patch fixes the check in skb_header_pointer to handle large
    positive offsets similar to skb_copy_bits. Invalid data can still
    be accessed using negative offsets (also similar to skb_copy_bits),
    anyone using negative offsets needs to verify them himself.
    
    Thanks to Thomas Vögtle <thomas.voegtle@coreworks.de> for verifying the
    problem by crashing his machine and providing me with an Oops.
    
    Signed-off-by: Patrick McHardy <kaber@trash.net>
    Signed-off-by: Chris Wright <chrisw@osdl.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>