Squashfs: add mount time sanity check for block_size and block_log match
Squashfs currently has a sanity check for block_size less than or equal to the maximum block_size (1 Mbyte). This catches some superblock corruption, but obviously with a block_size maximum of 1 Mbyte there's 7 correct values (4K, 8K, 16K, 32K, ... etc) and a lot of incorrect values which are not caught by this check. The Squashfs superblock, however, has both a block_size and a block_log (2^block_log == block_size). Checking that the block_size matches the block_log is a much more robust check. Corruption of the superblock is unlikely to produce values which match, and it also ensures the block_size is an exact power of two. Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
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@ -158,10 +158,15 @@ static int squashfs_fill_super(struct super_block *sb, void *data, int silent)
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goto failed_mount;
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}
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/* Check block log for sanity */
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msblk->block_log = le16_to_cpu(sblk->block_log);
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if (msblk->block_log > SQUASHFS_FILE_MAX_LOG)
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goto failed_mount;
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/* Check that block_size and block_log match */
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if (msblk->block_size != (1 << msblk->block_log))
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goto failed_mount;
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/* Check the root inode for sanity */
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root_inode = le64_to_cpu(sblk->root_inode);
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if (SQUASHFS_INODE_OFFSET(root_inode) > SQUASHFS_METADATA_SIZE)
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