Subject: + decompressors-fix-no-limit-output-buffer-length.patch added to -mm tree To: acourbot@xxxxxxxxxx,swarren@xxxxxxxxxxxxx,tixy@xxxxxxxxxx From: akpm@xxxxxxxxxxxxxxxxxxxx Date: Wed, 24 Jul 2013 13:47:27 -0700 The patch titled Subject: lib/decompressors: fix "no limit" output buffer length has been added to the -mm tree. Its filename is decompressors-fix-no-limit-output-buffer-length.patch This patch should soon appear at http://ozlabs.org/~akpm/mmots/broken-out/decompressors-fix-no-limit-output-buffer-length.patch and later at http://ozlabs.org/~akpm/mmotm/broken-out/decompressors-fix-no-limit-output-buffer-length.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/SubmitChecklist when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Alexandre Courbot <acourbot@xxxxxxxxxx> Subject: lib/decompressors: fix "no limit" output buffer length When decompressing into memory, the output buffer length is set to some arbitrarily high value (0x7fffffff) to indicate the output is, virtually, unlimited in size. The problem with this is that some platforms have their physical memory at high physical addresses (0x80000000 or more), and that the output buffer address and its "unlimited" length cannot be added without overflowing. An example of this can be found in inflate_fast(): /* next_out is the output buffer address */ out = strm->next_out - OFF; /* avail_out is the output buffer size. end will overflow if the output * address is >= 0x80000104 */ end = out + (strm->avail_out - 257); This has huge consequences on the performance of kernel decompression, since the following exit condition of inflate_fast() will be always true: } while (in < last && out < end); Indeed, "end" has overflowed and is now always lower than "out". As a result, inflate_fast() will return after processing one single byte of input data, and will thus need to be called an unreasonably high number of times. This probably went unnoticed because kernel decompression is fast enough even with this issue. Nonetheless, adjusting the output buffer length in such a way that the above pointer arithmetic never overflows results in a kernel decompression that is about 3 times faster on affected machines. Signed-off-by: Alexandre Courbot <acourbot@xxxxxxxxxx> Tested-by: Jon Medhurst <tixy@xxxxxxxxxx> Cc: Stephen Warren <swarren@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- lib/decompress_inflate.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff -puN lib/decompress_inflate.c~decompressors-fix-no-limit-output-buffer-length lib/decompress_inflate.c --- a/lib/decompress_inflate.c~decompressors-fix-no-limit-output-buffer-length +++ a/lib/decompress_inflate.c @@ -48,7 +48,7 @@ STATIC int INIT gunzip(unsigned char *bu out_len = 0x8000; /* 32 K */ out_buf = malloc(out_len); } else { - out_len = 0x7fffffff; /* no limit */ + out_len = ((size_t)~0) - (size_t)out_buf; /* no limit */ } if (!out_buf) { error("Out of memory while allocating output buffer"); _ Patches currently in -mm which might be from acourbot@xxxxxxxxxx are decompressors-fix-no-limit-output-buffer-length.patch -- To unsubscribe from this list: send the line "unsubscribe mm-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html