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From 2b32a7d82223d76ace432305b18c5816cadff878 Mon Sep 17 00:00:00 2001
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From: Florian Westphal <fw () strlen ! de>
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Date: Thu, 10 Mar 2016 00:56:02 -0800
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Subject: [PATCH] netfilter: x_tables: deal with bogus nextoffset values
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Ben Hawkes says:
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In the mark_source_chains function (net/ipv4/netfilter/ip_tables.c) it
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is possible for a user-supplied ipt_entry structure to have a large
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next_offset field. This field is not bounds checked prior to writing a
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counter value at the supplied offset.
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Problem is that xt_entry_foreach() macro stops iterating once e->next_offset
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is out of bounds, assuming this is the last entry.
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With malformed data thats not necessarily the case so we can
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write outside of allocated area later as we might not have walked the
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entire blob.
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Fix this by simplifying mark_source_chains -- it already has to check
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if nextoff is in range to catch invalid jumps, so just do the check
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when we move to a next entry as well.
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Signed-off-by: Florian Westphal <fw@strlen.de>
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---
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net/ipv4/netfilter/arp_tables.c | 8 ++++++++
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net/ipv4/netfilter/ip_tables.c | 8 ++++++++
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net/ipv6/netfilter/ip6_tables.c | 6 ++++++
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3 files changed, 22 insertions(+)
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diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
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index 2033f92..a9b6c76 100644
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--- a/net/ipv4/netfilter/arp_tables.c
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+++ b/net/ipv4/netfilter/arp_tables.c
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@@ -376,6 +376,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
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/* Move along one */
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size = e->next_offset;
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+
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+ if (pos + size > newinfo->size - sizeof(*e))
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+ return 0;
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+
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e = (struct arpt_entry *)
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(entry0 + pos + size);
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if (pos + size >= newinfo->size)
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@@ -399,6 +403,10 @@ static int mark_source_chains(const struct xt_table_info *newinfo,
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if (newpos >= newinfo->size)
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return 0;
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}
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+
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+ if (newpos > newinfo->size - sizeof(*e))
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+ return 0;
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+
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e = (struct arpt_entry *)
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(entry0 + newpos);
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e->counters.pcnt = pos;
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diff --git a/net/ipv4/netfilter/ip_tables.c b/net/ipv4/netfilter/ip_tables.c
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index 54906e0..7530ecd 100644
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--- a/net/ipv4/netfilter/ip_tables.c
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+++ b/net/ipv4/netfilter/ip_tables.c
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@@ -447,6 +447,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
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/* Move along one */
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size = e->next_offset;
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+
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+ if (pos + size > newinfo->size - sizeof(*e))
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+ return 0;
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+
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e = (struct ipt_entry *)
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(entry0 + pos + size);
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if (pos + size >= newinfo->size)
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@@ -470,6 +474,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
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if (newpos >= newinfo->size)
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return 0;
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}
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+
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+ if (newpos > newinfo->size - sizeof(*e))
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+ return 0;
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+
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e = (struct ipt_entry *)
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(entry0 + newpos);
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e->counters.pcnt = pos;
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diff --git a/net/ipv6/netfilter/ip6_tables.c b/net/ipv6/netfilter/ip6_tables.c
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index 63e06c3..894da69 100644
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--- a/net/ipv6/netfilter/ip6_tables.c
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+++ b/net/ipv6/netfilter/ip6_tables.c
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@@ -474,6 +474,8 @@ mark_source_chains(const struct xt_table_info *newinfo,
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/* Move along one */
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size = e->next_offset;
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+ if (pos + size > newinfo->size - sizeof(*e))
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+ return 0;
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e = (struct ip6t_entry *)
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(entry0 + pos + size);
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if (pos + size >= newinfo->size)
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@@ -497,6 +499,10 @@ mark_source_chains(const struct xt_table_info *newinfo,
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if (newpos >= newinfo->size)
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return 0;
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}
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+
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+ if (newpos > newinfo->size - sizeof(*e))
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+ return 0;
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+
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e = (struct ip6t_entry *)
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(entry0 + newpos);
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e->counters.pcnt = pos;
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--
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2.5.5
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