path: root/lib
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authorAlexandre Courbot <acourbot@nvidia.com>2013-09-11 14:23:53 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-02-06 11:08:12 -0800
commitc18e49ad50903819b947aea33c1cdcef724f7c35 (patch)
treee22f9e835801e311ee6730509e2049afdcbd9411 /lib
parent366d6b206f19ebe663503dbb58c2d05ab5f1b3f4 (diff)
lib/decompressors: fix "no limit" output buffer length
commit 1431574a1c4c669a0c198e4763627837416e4443 upstream. 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@nvidia.com> Tested-by: Jon Medhurst <tixy@linaro.org> Cc: Stephen Warren <swarren@wwwdotorg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mark Brown <broonie@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'lib')
1 files changed, 1 insertions, 1 deletions
diff --git a/lib/decompress_inflate.c b/lib/decompress_inflate.c
index 19ff89e34eec..d619b28c456f 100644
--- a/lib/decompress_inflate.c
+++ b/lib/decompress_inflate.c
@@ -48,7 +48,7 @@ STATIC int INIT gunzip(unsigned char *buf, int len,
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");