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The fix only affects Darwin, but to write the test I had to modify the MemoryMappingLayout class which is used by all OSes, to allow for mocking of image header (this change should be NFC). Hence no [Darwin] in the subject so I can get more eyes on it. While looking for a memory gap to put the shadow area into, the sanitizer code scans through the loaded images, and for each image it scans through its loader command to determine the occupied memory ranges. While doing so, if the 'segment load' (kLCSegment) loader comand is encountered, the command scanning function returns success (true), but does not decrement the command list iterator counter. The result is that the function is called again and again, with the iterator counter now being too high. The command scanner keeps updating the loader command pointer, by using the command size field. If the loop counter is too high, the command pointer lands into unintended area ( beyond <header addr>+sizeof(mac_header64)+header->sizeofcmds ), and result depends on the random content found there. The random content interpreted as loader command might contain a large integer value in the cmdsize field - this value is added to the current loader command pointer, which might now point to an inaccessible memory address. It can occasionally result in a crash if it happens to run beyond the mapped memory segment. Note that when the area after the loader command list contains zeros or small integers only, the loop will end normally and the problem will go unnoticed. So it happened until now since having a some big value after the header area, falling into command size field is a pretty rare situation. The fix makes sure that the iterator counter gets updated when the segment load (kLCSegment) loader command is found too, and in the same code location so the updates will always go together. Undo the changes in the sanitizer_procmaps_mac.cpp to see the test failing. rdar://101161047 rdar://102819707 Differential Revision: https://reviews.llvm.org/D142164
Compiler-RT ================================ This directory and its subdirectories contain source code for the compiler support routines. Compiler-RT is open source software. You may freely distribute it under the terms of the license agreement found in LICENSE.txt. ================================