125412 2013-12-08 06:24:59 -0800 Type punning error in MD5.cpp 2013-12-11 14:57:06 -0800 1 1 1 Unclassified WebKit New Bugs 528+ (Nightly build) Unspecified Unspecified RESOLVED FIXED P2 Normal --- 1 b.long b.long benjamin cmarcelo commit-queue darin oldest_to_newest 957608 0 b.long 2013-12-08 06:24:59 -0800 Type punning error in MD5.cpp 957609 1 b.long 2013-12-08 06:27:11 -0800 CXX Source/WTF/wtf/libWTF_la-MD5.lo ../../Source/WTF/wtf/MD5.cpp: In member function `void WTF::MD5::checksum(WTF::Vector<unsigned char, 16ul>&)': ../../Source/WTF/wtf/MD5.cpp:252:40: error: invalid cast from type `uint8_t {aka unsigned char}' to type `uint32_t {aka unsigned int}' reinterpret_cast_ptr<uint32_t>(m_in[56]) = m_bits[0]; ^ ../../Source/WTF/wtf/MD5.cpp:253:40: error: invalid cast from type `uint8_t {aka unsigned char}' to type `uint32_t {aka unsigned int}' reinterpret_cast_ptr<uint32_t>(m_in[60]) = m_bits[1]; ^ make: *** [Source/WTF/wtf/libWTF_la-MD5.lo] Error 1 I'm not exactly sure why this is bad, but from what I've read, this is a real problem because compilers are allowed to assume that this will never happen (for optimization purposes). We *are* allowed to cast pointers to char*, so I just reversed this to case the uint32_t to uint8_t instead of casting the uint8_t to uint32_t. 957610 2 218685 b.long 2013-12-08 06:28:58 -0800 Created attachment 218685 Patch 957636 3 b.long 2013-12-08 08:56:05 -0800 It was suggested that I use memcpy instead, since it's more efficient and possibly more clear. 957638 4 218692 b.long 2013-12-08 09:16:15 -0800 Created attachment 218692 Use memset 957639 5 b.long 2013-12-08 09:17:29 -0800 By the way, this was originally copied from SQLite, but it doesn't exist in their codebase anymore (otherwise I would fix it there too). 957997 6 218692 darin 2013-12-09 11:07:10 -0800 Comment on attachment 218692 Use memset View in context: https://bugs.webkit.org/attachment.cgi?id=218692&action=review > Source/WTF/wtf/MD5.cpp:66 > do { Not new to this patch, but it’s a little nutty that we run all this code in this reverseBytes function with the intention of doing nothing on little-endian machines! Sure would be nice to not do that. And the name of the function is silly since it does not reverse bytes on little-endian machines. > Source/WTF/wtf/MD5.cpp:70 > - *reinterpret_cast_ptr<uint32_t *>(buf) = t; > - buf += 4; > + memset(buf, t, sizeof(t)); > + buf += sizeof(t); The memset function converts its argument to an unsigned char, so this will discard the high bits of "t" and give us incorrect results. I’d expect this would be immediately visible because all MD5 digests would be wrong all the time. Did you test the code after changing it? > Source/WTF/wtf/MD5.cpp:252 > // Append length in bits and transform > // m_in is 4-byte aligned. > - (reinterpret_cast_ptr<uint32_t*>(m_in))[14] = m_bits[0]; > - (reinterpret_cast_ptr<uint32_t*>(m_in))[15] = m_bits[1]; > + memcpy(m_in + 56, m_bits, sizeof(m_bits)); This change looks OK, but I would remove the comment “m_in is 4-byte aligned” since the code no longer would be relying on that. 957998 7 darin 2013-12-09 11:08:17 -0800 (In reply to comment #5) > By the way, this was originally copied from SQLite, but it doesn't exist in their codebase anymore (otherwise I would fix it there too). Does SQLite have a newer version of the MD5 algorithm. Maybe we should adopt that? 958275 8 b.long 2013-12-10 04:07:06 -0800 (In reply to comment #7) > Does SQLite have a newer version of the MD5 algorithm. Maybe we should adopt that? No, they just removed it. Apparently md5.c was only used for tests of some kind. 958443 9 b.long 2013-12-10 11:50:22 -0800 I thought I ran WebKitBuild/Debug/Programs/TestWebKitAPI/TestWTF --gtest_filter=WTF_MD5* before, but apparently I did something wrong, since it definitely fails.. I'll fix this with memcpy. 958448 10 218889 b.long 2013-12-10 11:56:06 -0800 Created attachment 218889 Patch 958449 11 b.long 2013-12-10 11:56:58 -0800 I fixed things based on your comments, and the relevant test output is: $ WebKitBuild/Debug/Programs/TestWebKitAPI/TestWTF --gtest_filter=WTF_MD5* Note: Google Test filter = WTF_MD5* [==========] Running 1 test from 1 test case. [----------] Global test environment set-up. [----------] 1 test from WTF_MD5 [ RUN ] WTF_MD5.Computation [ OK ] WTF_MD5.Computation (0 ms) [----------] 1 test from WTF_MD5 (0 ms total) [----------] Global test environment tear-down [==========] 1 test from 1 test case ran. (0 ms total) [ PASSED ] 1 test. 958904 12 218889 darin 2013-12-11 14:22:22 -0800 Comment on attachment 218889 Patch Looks fine. 958930 13 218889 commit-queue 2013-12-11 14:57:04 -0800 Comment on attachment 218889 Patch Clearing flags on attachment: 218889 Committed r160460: <http://trac.webkit.org/changeset/160460> 958932 14 commit-queue 2013-12-11 14:57:06 -0800 All reviewed patches have been landed. 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