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From 5790cacab5a3fd7bde26056fa0f8b4650bd21bb7 Mon Sep 17 00:00:00 2001
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From: Phil Sutter <psutter@redhat.com>
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Date: Fri, 15 Mar 2019 17:50:10 +0100
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Subject: [PATCH] libxt_string: Fix array out of bounds check
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Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1525980
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Upstream Status: iptables commit 6fc7762f6f785
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commit 6fc7762f6f78526e3cb0c189ac2778a6be4c00b5
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Author: Phil Sutter <phil@nwl.cc>
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Date: Mon Sep 17 13:38:33 2018 +0200
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libxt_string: Fix array out of bounds check
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Commit 56d7ab42f3782 ("libxt_string: Avoid potential array out of bounds
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access") tried to fix parse_hex_string() for overlong strings but the
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change still allowed for 'sindex' to become XT_STRING_MAX_PATTERN_SIZE
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which leads to access of first byte after info->pattern. This is not
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really a problem because it merely overwrites info->patlen before
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calling xtables_error() later, but covscan still detects it so it's
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still worth fixing.
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The crucial bit here is that 'sindex' has to be incremented at end of
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the last iteration since its value is used for info->patlen. Hence just
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move the overflow check to the beginning of the loop.
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Fixes: 56d7ab42f3782 ("libxt_string: Avoid potential array out of bounds access")
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Signed-off-by: Phil Sutter <phil@nwl.cc>
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Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
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Signed-off-by: Phil Sutter <psutter@redhat.com>
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---
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extensions/libxt_string.c | 6 ++++--
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1 file changed, 4 insertions(+), 2 deletions(-)
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diff --git a/extensions/libxt_string.c b/extensions/libxt_string.c
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index d298c6a7081e7..7c6366cbbf1b3 100644
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--- a/extensions/libxt_string.c
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+++ b/extensions/libxt_string.c
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@@ -103,6 +103,9 @@ parse_hex_string(const char *s, struct xt_string_info *info)
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}
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while (i < slen) {
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+ if (sindex >= XT_STRING_MAX_PATTERN_SIZE)
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+ xtables_error(PARAMETER_PROBLEM,
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+ "STRING too long \"%s\"", s);
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if (s[i] == '\\' && !hex_f) {
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literal_f = 1;
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} else if (s[i] == '\\') {
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@@ -159,8 +162,7 @@ parse_hex_string(const char *s, struct xt_string_info *info)
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info->pattern[sindex] = s[i];
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i++;
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}
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- if (++sindex > XT_STRING_MAX_PATTERN_SIZE)
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- xtables_error(PARAMETER_PROBLEM, "STRING too long \"%s\"", s);
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+ sindex++;
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}
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info->patlen = sindex;
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}
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--
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2.21.0
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