kernel: ipv6: ip6_fragment: fix headroom tests and skb leak
Signed-off-by: Felix Fietkau <nbd@openwrt.org> SVN-Revision: 46992
This commit is contained in:
Felix Fietkau
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3 changed files with 203 additions and 1 deletions
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From: Florian Westphal <fw@strlen.de>
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Date: Thu, 17 Sep 2015 11:24:48 +0100
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Subject: [PATCH] ipv6: ip6_fragment: fix headroom tests and skb leak
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David Woodhouse reports skb_under_panic when we try to push ethernet
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header to fragmented ipv6 skbs:
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skbuff: skb_under_panic: text:c1277f1e len:1294 put:14 head:dec98000
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data:dec97ffc tail:0xdec9850a end:0xdec98f40 dev:br-lan
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[..]
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ip6_finish_output2+0x196/0x4da
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David further debugged this:
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[..] offending fragments were arriving here with skb_headroom(skb)==10.
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Which is reasonable, being the Solos ADSL card's header of 8 bytes
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followed by 2 bytes of PPP frame type.
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The problem is that if netfilter ipv6 defragmentation is used, skb_cow()
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in ip6_forward will only see reassembled skb.
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Therefore, headroom is overestimated by 8 bytes (we pulled fragment
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header) and we don't check the skbs in the frag_list either.
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We can't do these checks in netfilter defrag since outdev isn't known yet.
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Furthermore, existing tests in ip6_fragment did not consider the fragment
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or ipv6 header size when checking headroom of the fraglist skbs.
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While at it, also fix a skb leak on memory allocation -- ip6_fragment
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must consume the skb.
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I tested this e1000 driver hacked to not allocate additional headroom
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(we end up in slowpath, since LL_RESERVED_SPACE is 16).
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If 2 bytes of headroom are allocated, fastpath is taken (14 byte
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ethernet header was pulled, so 16 byte headroom available in all
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fragments).
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Reported-by: David Woodhouse <dwmw2@infradead.org>
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Diagnosed-by: David Woodhouse <dwmw2@infradead.org>
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Signed-off-by: Florian Westphal <fw@strlen.de>
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Closes 20532
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---
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--- a/net/ipv6/ip6_output.c
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+++ b/net/ipv6/ip6_output.c
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@@ -594,20 +594,22 @@ int ip6_fragment(struct sk_buff *skb, in
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}
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mtu -= hlen + sizeof(struct frag_hdr);
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+ hroom = LL_RESERVED_SPACE(rt->dst.dev);
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if (skb_has_frag_list(skb)) {
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int first_len = skb_pagelen(skb);
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struct sk_buff *frag2;
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if (first_len - hlen > mtu ||
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((first_len - hlen) & 7) ||
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- skb_cloned(skb))
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+ skb_cloned(skb) ||
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+ skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
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goto slow_path;
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skb_walk_frags(skb, frag) {
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/* Correct geometry. */
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if (frag->len > mtu ||
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((frag->len & 7) && frag->next) ||
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- skb_headroom(frag) < hlen)
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+ skb_headroom(frag) < (hlen + hroom + sizeof(struct frag_hdr)))
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goto slow_path_clean;
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/* Partially cloned skb? */
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@@ -624,8 +626,6 @@ int ip6_fragment(struct sk_buff *skb, in
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err = 0;
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offset = 0;
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- frag = skb_shinfo(skb)->frag_list;
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- skb_frag_list_init(skb);
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/* BUILD HEADER */
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*prevhdr = NEXTHDR_FRAGMENT;
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@@ -633,8 +633,11 @@ int ip6_fragment(struct sk_buff *skb, in
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if (!tmp_hdr) {
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IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
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IPSTATS_MIB_FRAGFAILS);
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- return -ENOMEM;
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+ err = -ENOMEM;
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+ goto fail;
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}
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+ frag = skb_shinfo(skb)->frag_list;
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+ skb_frag_list_init(skb);
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__skb_pull(skb, hlen);
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fh = (struct frag_hdr *)__skb_push(skb, sizeof(struct frag_hdr));
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@@ -732,7 +735,6 @@ slow_path:
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*/
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*prevhdr = NEXTHDR_FRAGMENT;
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- hroom = LL_RESERVED_SPACE(rt->dst.dev);
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troom = rt->dst.dev->needed_tailroom;
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/*
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@ -26,7 +26,7 @@ Signed-off-by: David S. Miller <davem@davemloft.net>
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--- a/net/ipv6/ip6_output.c
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+++ b/net/ipv6/ip6_output.c
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@@ -898,21 +898,45 @@ static int ip6_dst_lookup_tail(struct so
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@@ -900,21 +900,45 @@ static int ip6_dst_lookup_tail(struct so
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#endif
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int err;
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@ -0,0 +1,101 @@
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From: Florian Westphal <fw@strlen.de>
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Date: Thu, 17 Sep 2015 11:24:48 +0100
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Subject: [PATCH] ipv6: ip6_fragment: fix headroom tests and skb leak
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David Woodhouse reports skb_under_panic when we try to push ethernet
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header to fragmented ipv6 skbs:
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skbuff: skb_under_panic: text:c1277f1e len:1294 put:14 head:dec98000
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data:dec97ffc tail:0xdec9850a end:0xdec98f40 dev:br-lan
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[..]
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ip6_finish_output2+0x196/0x4da
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David further debugged this:
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[..] offending fragments were arriving here with skb_headroom(skb)==10.
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Which is reasonable, being the Solos ADSL card's header of 8 bytes
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followed by 2 bytes of PPP frame type.
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The problem is that if netfilter ipv6 defragmentation is used, skb_cow()
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in ip6_forward will only see reassembled skb.
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Therefore, headroom is overestimated by 8 bytes (we pulled fragment
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header) and we don't check the skbs in the frag_list either.
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We can't do these checks in netfilter defrag since outdev isn't known yet.
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Furthermore, existing tests in ip6_fragment did not consider the fragment
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or ipv6 header size when checking headroom of the fraglist skbs.
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While at it, also fix a skb leak on memory allocation -- ip6_fragment
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must consume the skb.
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I tested this e1000 driver hacked to not allocate additional headroom
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(we end up in slowpath, since LL_RESERVED_SPACE is 16).
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If 2 bytes of headroom are allocated, fastpath is taken (14 byte
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ethernet header was pulled, so 16 byte headroom available in all
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fragments).
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Reported-by: David Woodhouse <dwmw2@infradead.org>
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Diagnosed-by: David Woodhouse <dwmw2@infradead.org>
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Signed-off-by: Florian Westphal <fw@strlen.de>
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Closes 20532
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---
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--- a/net/ipv6/ip6_output.c
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+++ b/net/ipv6/ip6_output.c
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@@ -584,20 +584,22 @@ int ip6_fragment(struct sock *sk, struct
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}
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mtu -= hlen + sizeof(struct frag_hdr);
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+ hroom = LL_RESERVED_SPACE(rt->dst.dev);
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if (skb_has_frag_list(skb)) {
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int first_len = skb_pagelen(skb);
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struct sk_buff *frag2;
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if (first_len - hlen > mtu ||
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((first_len - hlen) & 7) ||
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- skb_cloned(skb))
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+ skb_cloned(skb) ||
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+ skb_headroom(skb) < (hroom + sizeof(struct frag_hdr)))
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goto slow_path;
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skb_walk_frags(skb, frag) {
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/* Correct geometry. */
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if (frag->len > mtu ||
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((frag->len & 7) && frag->next) ||
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- skb_headroom(frag) < hlen)
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+ skb_headroom(frag) < (hlen + hroom + sizeof(struct frag_hdr)))
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goto slow_path_clean;
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/* Partially cloned skb? */
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@@ -614,8 +616,6 @@ int ip6_fragment(struct sock *sk, struct
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err = 0;
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offset = 0;
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- frag = skb_shinfo(skb)->frag_list;
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- skb_frag_list_init(skb);
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/* BUILD HEADER */
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*prevhdr = NEXTHDR_FRAGMENT;
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@@ -623,8 +623,11 @@ int ip6_fragment(struct sock *sk, struct
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if (!tmp_hdr) {
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IP6_INC_STATS(net, ip6_dst_idev(skb_dst(skb)),
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IPSTATS_MIB_FRAGFAILS);
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- return -ENOMEM;
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+ err = -ENOMEM;
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+ goto fail;
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}
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+ frag = skb_shinfo(skb)->frag_list;
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+ skb_frag_list_init(skb);
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__skb_pull(skb, hlen);
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fh = (struct frag_hdr *)__skb_push(skb, sizeof(struct frag_hdr));
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@@ -722,7 +725,6 @@ slow_path:
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*/
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*prevhdr = NEXTHDR_FRAGMENT;
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- hroom = LL_RESERVED_SPACE(rt->dst.dev);
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troom = rt->dst.dev->needed_tailroom;
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/*
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