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| author | Dave Rodgman <dave.rodgman@arm.com> | 2020-06-11 17:34:54 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-06-11 18:17:47 -0700 |
| commit | b5265c813ce4efbfa2e46fd27cdf9a7f44a35d2e (patch) | |
| tree | 28486c04a70a504864e588d1b341dab1140558b9 /lib/lzo | |
| parent | fce1affe4e39b9ca8346bdbb5171e60ac303c355 (diff) | |
| download | lwn-b5265c813ce4efbfa2e46fd27cdf9a7f44a35d2e.tar.gz lwn-b5265c813ce4efbfa2e46fd27cdf9a7f44a35d2e.zip | |
lib/lzo: fix ambiguous encoding bug in lzo-rle
In some rare cases, for input data over 32 KB, lzo-rle could encode two
different inputs to the same compressed representation, so that
decompression is then ambiguous (i.e. data may be corrupted - although
zram is not affected because it operates over 4 KB pages).
This modifies the compressor without changing the decompressor or the
bitstream format, such that:
- there is no change to how data produced by the old compressor is
decompressed
- an old decompressor will correctly decode data from the updated
compressor
- performance and compression ratio are not affected
- we avoid introducing a new bitstream format
In testing over 12.8M real-world files totalling 903 GB, three files
were affected by this bug. I also constructed 37M semi-random 64 KB
files totalling 2.27 TB, and saw no affected files. Finally I tested
over files constructed to contain each of the ~1024 possible bad input
sequences; for all of these cases, updated lzo-rle worked correctly.
There is no significant impact to performance or compression ratio.
Signed-off-by: Dave Rodgman <dave.rodgman@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Dave Rodgman <dave.rodgman@arm.com>
Cc: Willy Tarreau <w@1wt.eu>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Markus F.X.J. Oberhumer <markus@oberhumer.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: <stable@vger.kernel.org>
Link: http://lkml.kernel.org/r/20200507100203.29785-1-dave.rodgman@arm.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'lib/lzo')
| -rw-r--r-- | lib/lzo/lzo1x_compress.c | 13 |
1 files changed, 13 insertions, 0 deletions
diff --git a/lib/lzo/lzo1x_compress.c b/lib/lzo/lzo1x_compress.c index 717c940112f9..8ad5ba2b86e2 100644 --- a/lib/lzo/lzo1x_compress.c +++ b/lib/lzo/lzo1x_compress.c @@ -268,6 +268,19 @@ m_len_done: *op++ = (M4_MARKER | ((m_off >> 11) & 8) | (m_len - 2)); else { + if (unlikely(((m_off & 0x403f) == 0x403f) + && (m_len >= 261) + && (m_len <= 264)) + && likely(bitstream_version)) { + // Under lzo-rle, block copies + // for 261 <= length <= 264 and + // (distance & 0x80f3) == 0x80f3 + // can result in ambiguous + // output. Adjust length + // to 260 to prevent ambiguity. + ip -= m_len - 260; + m_len = 260; + } m_len -= M4_MAX_LEN; *op++ = (M4_MARKER | ((m_off >> 11) & 8)); while (unlikely(m_len > 255)) { |