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authorFilipe David Borba Manana <fdmanana@gmail.com>2014-02-08 15:47:46 +0000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-03-23 21:38:20 -0700
commit0e48f06cf0a1b55cd2dcc432ccfb13174705fcc2 (patch)
treec29a49cd7506ee1f29919da469951e29fac9589c /fs
parentd2c6966a096ad50c33825a52e6521102ffeda1ff (diff)
downloadlinaro-lsk-0e48f06cf0a1b55cd2dcc432ccfb13174705fcc2.tar.gz
Btrfs: fix data corruption when reading/updating compressed extents
commit a2aa75e18a21b21952dc6daa9bac7c9f4426f81f upstream. When using a mix of compressed file extents and prealloc extents, it is possible to fill a page of a file with random, garbage data from some unrelated previous use of the page, instead of a sequence of zeroes. A simple sequence of steps to get into such case, taken from the test case I made for xfstests, is: _scratch_mkfs _scratch_mount "-o compress-force=lzo" $XFS_IO_PROG -f -c "pwrite -S 0x06 -b 18670 266978 18670" $SCRATCH_MNT/foobar $XFS_IO_PROG -c "falloc 26450 665194" $SCRATCH_MNT/foobar $XFS_IO_PROG -c "truncate 542872" $SCRATCH_MNT/foobar $XFS_IO_PROG -c "fsync" $SCRATCH_MNT/foobar This results in the following file items in the fs tree: item 4 key (257 INODE_ITEM 0) itemoff 15879 itemsize 160 inode generation 6 transid 6 size 542872 block group 0 mode 100600 item 5 key (257 INODE_REF 256) itemoff 15863 itemsize 16 inode ref index 2 namelen 6 name: foobar item 6 key (257 EXTENT_DATA 0) itemoff 15810 itemsize 53 extent data disk byte 0 nr 0 gen 6 extent data offset 0 nr 24576 ram 266240 extent compression 0 item 7 key (257 EXTENT_DATA 24576) itemoff 15757 itemsize 53 prealloc data disk byte 12849152 nr 241664 gen 6 prealloc data offset 0 nr 241664 item 8 key (257 EXTENT_DATA 266240) itemoff 15704 itemsize 53 extent data disk byte 12845056 nr 4096 gen 6 extent data offset 0 nr 20480 ram 20480 extent compression 2 item 9 key (257 EXTENT_DATA 286720) itemoff 15651 itemsize 53 prealloc data disk byte 13090816 nr 405504 gen 6 prealloc data offset 0 nr 258048 The on disk extent at offset 266240 (which corresponds to 1 single disk block), contains 5 compressed chunks of file data. Each of the first 4 compress 4096 bytes of file data, while the last one only compresses 3024 bytes of file data. Therefore a read into the file region [285648 ; 286720[ (length = 4096 - 3024 = 1072 bytes) should always return zeroes (our next extent is a prealloc one). The solution here is the compression code path to zero the remaining (untouched) bytes of the last page it uncompressed data into, as the information about how much space the file data consumes in the last page is not known in the upper layer fs/btrfs/extent_io.c:__do_readpage(). In __do_readpage we were correctly zeroing the remainder of the page but only if it corresponds to the last page of the inode and if the inode's size is not a multiple of the page size. This would cause not only returning random data on reads, but also permanently storing random data when updating parts of the region that should be zeroed. For the example above, it means updating a single byte in the region [285648 ; 286720[ would store that byte correctly but also store random data on disk. A test case for xfstests follows soon. Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com> Signed-off-by: Chris Mason <clm@fb.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/btrfs/compression.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index b189bd1e7a3..ce7067881d3 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -1009,6 +1009,8 @@ int btrfs_decompress_buf2page(char *buf, unsigned long buf_start,
bytes = min(bytes, working_bytes);
kaddr = kmap_atomic(page_out);
memcpy(kaddr + *pg_offset, buf + buf_offset, bytes);
+ if (*pg_index == (vcnt - 1) && *pg_offset == 0)
+ memset(kaddr + bytes, 0, PAGE_CACHE_SIZE - bytes);
kunmap_atomic(kaddr);
flush_dcache_page(page_out);