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From 0adcb34c49bee5b19bd29b16a578c510c23597ea Mon Sep 17 00:00:00 2001
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From: Sebastian Pipping <sebastian@pipping.org>
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Date: Mon, 27 Dec 2021 20:15:02 +0100
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Subject: [PATCH] lib: Detect and prevent troublesome left shifts in function
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storeAtts (CVE-2021-45960)
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---
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expat/lib/xmlparse.c | 31 +++++++++++++++++++++++++++++--
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1 file changed, 29 insertions(+), 2 deletions(-)
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diff --git a/lib/xmlparse.c b/lib/xmlparse.c
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index d730f41c3..b47c31b05 100644
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--- a/lib/xmlparse.c
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+++ b/lib/xmlparse.c
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@@ -3414,7 +3414,13 @@ storeAtts(XML_Parser parser, const ENCODING *enc, const char *attStr,
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if (nPrefixes) {
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int j; /* hash table index */
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unsigned long version = parser->m_nsAttsVersion;
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- int nsAttsSize = (int)1 << parser->m_nsAttsPower;
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+
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+ /* Detect and prevent invalid shift */
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+ if (parser->m_nsAttsPower >= sizeof(unsigned int) * 8 /* bits per byte */) {
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+ return XML_ERROR_NO_MEMORY;
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+ }
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+
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+ unsigned int nsAttsSize = 1u << parser->m_nsAttsPower;
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unsigned char oldNsAttsPower = parser->m_nsAttsPower;
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/* size of hash table must be at least 2 * (# of prefixed attributes) */
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if ((nPrefixes << 1)
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@@ -3425,7 +3431,28 @@ storeAtts(XML_Parser parser, const ENCODING *enc, const char *attStr,
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;
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if (parser->m_nsAttsPower < 3)
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parser->m_nsAttsPower = 3;
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- nsAttsSize = (int)1 << parser->m_nsAttsPower;
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+
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+ /* Detect and prevent invalid shift */
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+ if (parser->m_nsAttsPower >= sizeof(nsAttsSize) * 8 /* bits per byte */) {
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+ /* Restore actual size of memory in m_nsAtts */
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+ parser->m_nsAttsPower = oldNsAttsPower;
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+ return XML_ERROR_NO_MEMORY;
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+ }
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+
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+ nsAttsSize = 1u << parser->m_nsAttsPower;
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+
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+ /* Detect and prevent integer overflow.
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+ * The preprocessor guard addresses the "always false" warning
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+ * from -Wtype-limits on platforms where
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+ * sizeof(unsigned int) < sizeof(size_t), e.g. on x86_64. */
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+#if UINT_MAX >= SIZE_MAX
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+ if (nsAttsSize > (size_t)(-1) / sizeof(NS_ATT)) {
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+ /* Restore actual size of memory in m_nsAtts */
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+ parser->m_nsAttsPower = oldNsAttsPower;
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+ return XML_ERROR_NO_MEMORY;
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+ }
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+#endif
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+
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temp = (NS_ATT *)REALLOC(parser, parser->m_nsAtts,
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nsAttsSize * sizeof(NS_ATT));
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if (! temp) {
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