expat: fix CVE-2021-45960

In Expat (aka libexpat) before 2.4.3, a left shift by 29 (or more)
places in the storeAtts function in xmlparse.c can lead to realloc
misbehavior (e.g., allocating too few bytes, or only freeing memory).

Backport patch from:
https://github.com/libexpat/libexpat/pull/534/commits/0adcb34c49bee5b19bd29b16a578c510c23597ea

CVE: CVE-2021-45960
(From OE-Core rev: 22fe1dea3164a5cd4d5636376f3671641ada1da9)

Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-core/expat/expat/CVE-2021-45960.patch

@@ -0,0 +1,65 @@
+From 0adcb34c49bee5b19bd29b16a578c510c23597ea Mon Sep 17 00:00:00 2001
+From: Sebastian Pipping <sebastian@pipping.org>
+Date: Mon, 27 Dec 2021 20:15:02 +0100
+Subject: [PATCH] lib: Detect and prevent troublesome left shifts in function
+ storeAtts (CVE-2021-45960)
+
+Upstream-Status: Backport:
+https://github.com/libexpat/libexpat/pull/534/commits/0adcb34c49bee5b19bd29b16a578c510c23597ea
+
+CVE: CVE-2021-45960
+Signed-off-by: Steve Sakoman <steve@sakoman.com>
+
+---
+ expat/lib/xmlparse.c | 31 +++++++++++++++++++++++++++++--
+ 1 file changed, 29 insertions(+), 2 deletions(-)
+
+diff --git a/expat/lib/xmlparse.c b/expat/lib/xmlparse.c
+index d730f41c3..b47c31b05 100644
+--- a/lib/xmlparse.c
++++ b/lib/xmlparse.c
+@@ -3414,7 +3414,13 @@ storeAtts(XML_Parser parser, const ENCODING *enc, const char *attStr,
+   if (nPrefixes) {
+     int j; /* hash table index */
+     unsigned long version = parser->m_nsAttsVersion;
+-    int nsAttsSize = (int)1 << parser->m_nsAttsPower;
++
++    /* Detect and prevent invalid shift */
++    if (parser->m_nsAttsPower >= sizeof(unsigned int) * 8 /* bits per byte */) {
++      return XML_ERROR_NO_MEMORY;
++    }
++
++    unsigned int nsAttsSize = 1u << parser->m_nsAttsPower;
+     unsigned char oldNsAttsPower = parser->m_nsAttsPower;
+     /* size of hash table must be at least 2 * (# of prefixed attributes) */
+     if ((nPrefixes << 1)
+@@ -3425,7 +3431,28 @@ storeAtts(XML_Parser parser, const ENCODING *enc, const char *attStr,
+         ;
+       if (parser->m_nsAttsPower < 3)
+         parser->m_nsAttsPower = 3;
+-      nsAttsSize = (int)1 << parser->m_nsAttsPower;
++
++      /* Detect and prevent invalid shift */
++      if (parser->m_nsAttsPower >= sizeof(nsAttsSize) * 8 /* bits per byte */) {
++        /* Restore actual size of memory in m_nsAtts */
++        parser->m_nsAttsPower = oldNsAttsPower;
++        return XML_ERROR_NO_MEMORY;
++      }
++
++      nsAttsSize = 1u << parser->m_nsAttsPower;
++
++      /* Detect and prevent integer overflow.
++       * The preprocessor guard addresses the "always false" warning
++       * from -Wtype-limits on platforms where
++       * sizeof(unsigned int) < sizeof(size_t), e.g. on x86_64. */
++#if UINT_MAX >= SIZE_MAX
++      if (nsAttsSize > (size_t)(-1) / sizeof(NS_ATT)) {
++        /* Restore actual size of memory in m_nsAtts */
++        parser->m_nsAttsPower = oldNsAttsPower;
++        return XML_ERROR_NO_MEMORY;
++      }
++#endif
++
+       temp = (NS_ATT *)REALLOC(parser, parser->m_nsAtts,
+                                nsAttsSize * sizeof(NS_ATT));
+       if (! temp) {

meta/recipes-core/expat/expat_2.2.9.bb

@@ -8,6 +8,7 @@ LIC_FILES_CHKSUM = "file://COPYING;md5=5b8620d98e49772d95fc1d291c26aa79"
 
 SRC_URI = "git://github.com/libexpat/libexpat.git;protocol=https;branch=master \
            file://CVE-2013-0340.patch \
+           file://CVE-2021-45960.patch \
            file://CVE-2022-22822-27.patch \
            file://libtool-tag.patch \
          "