# HG changeset patch
# User Augie Fackler <augie@google.com>
# Date 1528899884 14400
# Node ID 1fb2510cf8c81f2e26ec49054fdbec67ec56cba0
# Parent  74b4a54002ecb2059612d5e69ba204d05c818542
bitmanipulation: fix undefined behavior in bit shift in getbe32

OSS-Fuzz caught this in its ubsan mode[0]. I'm not worried about a
security issue here because in practice this should work out the way
we naively expected, we're just making things explicit to the
compiler with the casts.

0: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=8876

Differential Revision: https://phab.mercurial-scm.org/D3729

diff -r 74b4a54002ec -r 1fb2510cf8c8 contrib/fuzz/mpatch_corpus.py
--- a/contrib/fuzz/mpatch_corpus.py	Wed Jun 13 21:58:42 2018 +0900
+++ b/contrib/fuzz/mpatch_corpus.py	Wed Jun 13 10:24:44 2018 -0400
@@ -78,6 +78,10 @@
     zf.writestr(
         "mpatch_decode_old_overread", "\x02\x00\x00\x00\x02\x00\x00\x00"
     )
+    # https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=8876
+    zf.writestr(
+        "mpatch_ossfuzz_getbe32_ubsan",
+        "\x02\x00\x00\x00\x0c    \xff\xff\xff\xff    ")
     zf.writestr(
         "mpatch_apply_over_memcpy",
         '\x13\x01\x00\x05\xd0\x00\x00\x00\x00\x00\x00\x00\x00\n \x00\x00\x00'
diff -r 74b4a54002ec -r 1fb2510cf8c8 mercurial/bitmanipulation.h
--- a/mercurial/bitmanipulation.h	Wed Jun 13 21:58:42 2018 +0900
+++ b/mercurial/bitmanipulation.h	Wed Jun 13 10:24:44 2018 -0400
@@ -9,7 +9,8 @@
 {
 	const unsigned char *d = (const unsigned char *)c;
 
-	return ((d[0] << 24) | (d[1] << 16) | (d[2] << 8) | (d[3]));
+	return ((((uint32_t)d[0]) << 24) | (((uint32_t)d[1]) << 16) |
+	        (((uint32_t)d[2]) << 8) | (d[3]));
 }
 
 static inline int16_t getbeint16(const char *c)