Patchwork D3729: bitmanipulation: fix undefined behavior in bit shift in getbe32

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Submitter phabricator
Date June 13, 2018, 2:25 p.m.
Message ID <differential-rev-PHID-DREV-mw7wheo55kd6xaled4l3-req@phab.mercurial-scm.org>
Download mbox | patch
Permalink /patch/32117/
State Superseded
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phabricator - June 13, 2018, 2:25 p.m.
durin42 created this revision.
Herald added a subscriber: mercurial-devel.
Herald added a reviewer: hg-reviewers.

REVISION SUMMARY
  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

REPOSITORY
  rHG Mercurial

REVISION DETAIL
  https://phab.mercurial-scm.org/D3729

AFFECTED FILES
  contrib/fuzz/mpatch_corpus.py
  mercurial/bitmanipulation.h

CHANGE DETAILS




To: durin42, #hg-reviewers
Cc: mercurial-devel

Patch

diff --git a/mercurial/bitmanipulation.h b/mercurial/bitmanipulation.h
--- a/mercurial/bitmanipulation.h
+++ b/mercurial/bitmanipulation.h
@@ -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)
diff --git a/contrib/fuzz/mpatch_corpus.py b/contrib/fuzz/mpatch_corpus.py
--- a/contrib/fuzz/mpatch_corpus.py
+++ b/contrib/fuzz/mpatch_corpus.py
@@ -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'