Re: [PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment

From: kbuild test robot
Date: Tue Apr 02 2019 - 07:04:18 EST

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In reply to: hujunwei: "[PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment"
Next in thread: Martin Lau: "Re: [PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment"
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Hi hujunwei,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on net/master]

url: https://github.com/0day-ci/linux/commits/hujunwei/ipv6-Fix-dangling-pointer-when-ipv6-fragment/20190402-175602
config: i386-randconfig-x005-201913 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386

All warnings (new ones prefixed by >>):

net//ipv6/ip6_output.c: In function 'ip6_fragment':
>> net//ipv6/ip6_output.c:609:27: warning: 'prevhdr' is used uninitialized in this function [-Wuninitialized]
nexthdr_offset = prevhdr - skb_network_header(skb);
~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

vim +/prevhdr +609 net//ipv6/ip6_output.c

594
595 int ip6_fragment(struct net *net, struct sock *sk, struct sk_buff *skb,
596 int (*output)(struct net *, struct sock *, struct sk_buff *))
597 {
598 struct sk_buff *frag;
599 struct rt6_info *rt = (struct rt6_info *)skb_dst(skb);
600 struct ipv6_pinfo *np = skb->sk && !dev_recursion_level() ?
601 inet6_sk(skb->sk) : NULL;
602 struct ipv6hdr *tmp_hdr;
603 struct frag_hdr *fh;
604 unsigned int mtu, hlen, left, len, nexthdr_offset;
605 int hroom, troom;
606 __be32 frag_id;
607 int ptr, offset = 0, err = 0;
608 u8 *prevhdr, nexthdr = 0;
> 609 nexthdr_offset = prevhdr - skb_network_header(skb);
610
611 err = ip6_find_1stfragopt(skb, &prevhdr);
612 if (err < 0)
613 goto fail;
614 hlen = err;
615 nexthdr = *prevhdr;
616
617 mtu = ip6_skb_dst_mtu(skb);
618
619 /* We must not fragment if the socket is set to force MTU discovery
620 * or if the skb it not generated by a local socket.
621 */
622 if (unlikely(!skb->ignore_df && skb->len > mtu))
623 goto fail_toobig;
624
625 if (IP6CB(skb)->frag_max_size) {
626 if (IP6CB(skb)->frag_max_size > mtu)
627 goto fail_toobig;
628
629 /* don't send fragments larger than what we received */
630 mtu = IP6CB(skb)->frag_max_size;
631 if (mtu < IPV6_MIN_MTU)
632 mtu = IPV6_MIN_MTU;
633 }
634
635 if (np && np->frag_size < mtu) {
636 if (np->frag_size)
637 mtu = np->frag_size;
638 }
639 if (mtu < hlen + sizeof(struct frag_hdr) + 8)
640 goto fail_toobig;
641 mtu -= hlen + sizeof(struct frag_hdr);
642
643 frag_id = ipv6_select_ident(net, &ipv6_hdr(skb)->daddr,
644 &ipv6_hdr(skb)->saddr);
645
646 if (skb->ip_summed == CHECKSUM_PARTIAL &&
647 (err = skb_checksum_help(skb)))
648 goto fail;
649
650 prevhdr = skb_network_header(skb) + nexthdr_offset;
651 hroom = LL_RESERVED_SPACE(rt->dst.dev);
652 if (skb_has_frag_list(skb)) {
653 unsigned int first_len = skb_pagelen(skb);
654 struct sk_buff *frag2;
655
656 if (first_len - hlen > mtu ||
657 ((first_len - hlen) & 7) ||
658 skb_cloned(skb) ||
659 skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
660 goto slow_path;
661
662 skb_walk_frags(skb, frag) {
663 /* Correct geometry. */
664 if (frag->len > mtu ||
665 ((frag->len & 7) && frag->next) ||
666 skb_headroom(frag) < (hlen + hroom + sizeof(struct frag_hdr)))
667 goto slow_path_clean;
668
669 /* Partially cloned skb? */
670 if (skb_shared(frag))
671 goto slow_path_clean;
672
673 BUG_ON(frag->sk);
674 if (skb->sk) {
675 frag->sk = skb->sk;
676 frag->destructor = sock_wfree;
677 }
678 skb->truesize -= frag->truesize;
679 }
680
681 err = 0;
682 offset = 0;
683 /* BUILD HEADER */
684
685 *prevhdr = NEXTHDR_FRAGMENT;
686 tmp_hdr = kmemdup(skb_network_header(skb), hlen, GFP_ATOMIC);
687 if (!tmp_hdr) {
688 err = -ENOMEM;
689 goto fail;
690 }
691 frag = skb_shinfo(skb)->frag_list;
692 skb_frag_list_init(skb);
693
694 __skb_pull(skb, hlen);
695 fh = __skb_push(skb, sizeof(struct frag_hdr));
696 __skb_push(skb, hlen);
697 skb_reset_network_header(skb);
698 memcpy(skb_network_header(skb), tmp_hdr, hlen);
699
700 fh->nexthdr = nexthdr;
701 fh->reserved = 0;
702 fh->frag_off = htons(IP6_MF);
703 fh->identification = frag_id;
704
705 first_len = skb_pagelen(skb);
706 skb->data_len = first_len - skb_headlen(skb);
707 skb->len = first_len;
708 ipv6_hdr(skb)->payload_len = htons(first_len -
709 sizeof(struct ipv6hdr));
710
711 for (;;) {
712 /* Prepare header of the next frame,
713 * before previous one went down. */
714 if (frag) {
715 frag->ip_summed = CHECKSUM_NONE;
716 skb_reset_transport_header(frag);
717 fh = __skb_push(frag, sizeof(struct frag_hdr));
718 __skb_push(frag, hlen);
719 skb_reset_network_header(frag);
720 memcpy(skb_network_header(frag), tmp_hdr,
721 hlen);
722 offset += skb->len - hlen - sizeof(struct frag_hdr);
723 fh->nexthdr = nexthdr;
724 fh->reserved = 0;
725 fh->frag_off = htons(offset);
726 if (frag->next)
727 fh->frag_off |= htons(IP6_MF);
728 fh->identification = frag_id;
729 ipv6_hdr(frag)->payload_len =
730 htons(frag->len -
731 sizeof(struct ipv6hdr));
732 ip6_copy_metadata(frag, skb);
733 }
734
735 err = output(net, sk, skb);
736 if (!err)
737 IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
738 IPSTATS_MIB_FRAGCREATES);
739
740 if (err || !frag)
741 break;
742
743 skb = frag;
744 frag = skb->next;
745 skb_mark_not_on_list(skb);
746 }
747
748 kfree(tmp_hdr);
749
750 if (err == 0) {
751 IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
752 IPSTATS_MIB_FRAGOKS);
753 return 0;
754 }
755
756 kfree_skb_list(frag);
757
758 IP6_INC_STATS(net, ip6_dst_idev(&rt->dst),
759 IPSTATS_MIB_FRAGFAILS);
760 return err;
761
762 slow_path_clean:
763 skb_walk_frags(skb, frag2) {
764 if (frag2 == frag)
765 break;
766 frag2->sk = NULL;
767 frag2->destructor = NULL;
768 skb->truesize += frag2->truesize;
769 }
770 }
771
772 slow_path:
773 left = skb->len - hlen; /* Space per frame */
774 ptr = hlen; /* Where to start from */
775
776 /*
777 * Fragment the datagram.
778 */
779
780 troom = rt->dst.dev->needed_tailroom;
781
782 /*
783 * Keep copying data until we run out.
784 */
785 while (left > 0) {
786 u8 *fragnexthdr_offset;
787
788 len = left;
789 /* IF: it doesn't fit, use 'mtu' - the data space left */
790 if (len > mtu)
791 len = mtu;
792 /* IF: we are not sending up to and including the packet end
793 then align the next start on an eight byte boundary */
794 if (len < left) {
795 len &= ~7;
796 }
797
798 /* Allocate buffer */
799 frag = alloc_skb(len + hlen + sizeof(struct frag_hdr) +
800 hroom + troom, GFP_ATOMIC);
801 if (!frag) {
802 err = -ENOMEM;
803 goto fail;
804 }
805
806 /*
807 * Set up data on packet
808 */
809
810 ip6_copy_metadata(frag, skb);
811 skb_reserve(frag, hroom);
812 skb_put(frag, len + hlen + sizeof(struct frag_hdr));
813 skb_reset_network_header(frag);
814 fh = (struct frag_hdr *)(skb_network_header(frag) + hlen);
815 frag->transport_header = (frag->network_header + hlen +
816 sizeof(struct frag_hdr));
817
818 /*
819 * Charge the memory for the fragment to any owner
820 * it might possess
821 */
822 if (skb->sk)
823 skb_set_owner_w(frag, skb->sk);
824
825 /*
826 * Copy the packet header into the new buffer.
827 */
828 skb_copy_from_linear_data(skb, skb_network_header(frag), hlen);
829
830 fragnexthdr_offset = skb_network_header(frag);
831 fragnexthdr_offset += prevhdr - skb_network_header(skb);
832 *fragnexthdr_offset = NEXTHDR_FRAGMENT;
833
834 /*
835 * Build fragment header.
836 */
837 fh->nexthdr = nexthdr;
838 fh->reserved = 0;
839 fh->identification = frag_id;
840
841 /*
842 * Copy a block of the IP datagram.
843 */
844 BUG_ON(skb_copy_bits(skb, ptr, skb_transport_header(frag),
845 len));
846 left -= len;
847
848 fh->frag_off = htons(offset);
849 if (left > 0)
850 fh->frag_off |= htons(IP6_MF);
851 ipv6_hdr(frag)->payload_len = htons(frag->len -
852 sizeof(struct ipv6hdr));
853
854 ptr += len;
855 offset += len;
856
857 /*
858 * Put this fragment into the sending queue.
859 */
860 err = output(net, sk, frag);
861 if (err)
862 goto fail;
863
864 IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
865 IPSTATS_MIB_FRAGCREATES);
866 }
867 IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
868 IPSTATS_MIB_FRAGOKS);
869 consume_skb(skb);
870 return err;
871
872 fail_toobig:
873 if (skb->sk && dst_allfrag(skb_dst(skb)))
874 sk_nocaps_add(skb->sk, NETIF_F_GSO_MASK);
875
876 icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, mtu);
877 err = -EMSGSIZE;
878
879 fail:
880 IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
881 IPSTATS_MIB_FRAGFAILS);
882 kfree_skb(skb);
883 return err;
884 }
885

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Next message: Sekhar Nori: "Re: [RESEND PATCH 1/2] ARM: davinci: support multiplatform build for ARM v5"
Previous message: Bartlomiej Zolnierkiewicz: "Re: [PATCH] video: fbdev: sis: fix a missing-check bug"
In reply to: hujunwei: "[PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment"
Next in thread: Martin Lau: "Re: [PATCH v3 net] ipv6: Fix dangling pointer when ipv6 fragment"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]