Messages in this thread | | | From | Chandan Rajendra <> | Subject | Re: [PATCH 1/2] ext4: fix warning about stack corruption | Date | Mon, 07 Aug 2017 12:12:33 +0530 |
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On Tuesday, August 1, 2017 5:34:03 PM IST Arnd Bergmann wrote: > After commit 62d1034f53e3 ("fortify: use WARN instead of BUG for now"), > we get a warning about possible stack overflow from a memcpy that > was not strictly bounded to the size of the local variable: > > inlined from 'ext4_mb_seq_groups_show' at fs/ext4/mballoc.c:2322:2: > include/linux/string.h:309:9: error: '__builtin_memcpy': writing between 161 and 1116 bytes into a region of size 160 overflows the destination [-Werror=stringop-overflow=] > > We actually had a bug here that would have been found by the warning, > but it was already fixed last year in commit 30a9d7afe70e ("ext4: fix > stack memory corruption with 64k block size"). > > This replaces the fixed-length structure on the stack with a variable-length > structure, using the correct upper bound that tells the compiler that > everything is really fine here. I also change the loop count to check > for the same upper bound for consistency, but the existing code is > already correct here. > > Note that while clang won't allow certain kinds of variable-length arrays > in structures, this particular instance is fine, as the array is at the > end of the structure, and the size is strictly bounded. > > There is one remaining issue with the function that I'm not addressing > here: With s_blocksize_bits==16, we don't actually print the last two > members of the array, as we loop though just the first 14 members. > This could be easily addressed by adding two extra columns in the output, > but that could in theory break parsers in user space, and should be > a separate patch if we decide to modify it. >
I executed xfstests on a ppc64 machine with both 4k and 64k block size combination.
Tested-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
-- chandan
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