Re: [PATCH] fs/squashfs: Fix some hardlinks reading the wrong inode

[Tom Rini <trini@konsulko.com>]

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On Fri, Apr 30, 2021 at 04:45:46PM +1200, Campbell Suter wrote:

> In SquashFS, the contents of a directory is stored by
> squashfs_directory_entry structures which contain the file's name, inode
> and position within the filesystem.
> 
> The inode number is not stored directly; instead each directory has one
> or more headers which set a base inode number, and files store the
> offset from that to the file's inode number.
> 
> In mksquashfs, each inode is allocated a number in the same order as
> they are written to the directory table; thus the offset from the
> header's base inode number to the file's inode number is usually
> positive.
> 
> Hardlinks are simply stored with two directory entries referencing the
> same file. This means the second entry will thus have an inode number
> much lower than the surrounding files. Since the header's base inode
> number comes from the first entry that uses the header, this delta will
> usually be negative.
> 
> Previously, U-Boot's squashfs_directory_entry.inode_offset field was
> declared as an unsigned value. Thus when a negative value was found, it
> would either resolve to an invalid inode number or to that of an
> unrelated file.
> 
> A squashfs image to test this can be created like so:
> 
>     echo hi > sqfs_test_files/001-root-file
>     mkdir     sqfs_test_files/002-subdir
>     touch     sqfs_test_files/002-subdir/003-file
>     ln        sqfs_test_files/{001-root-file,002-subdir/004-link}
>     mksquashfs sqfs_test_files/ test.sqfs -noappend
> 
> Note that squashfs sorts the files ASCIIbetacally, so we can use the
> names to control the order they appear in. The ordering is important -
> the first reference to the file must have a lower inode number than the
> directory in which the second reference resides, and the second
> reference cannot be the first file in the directory.
> 
> Listing this sample image in U-Boot results in:
> 
> => sqfsls virtio 2 002-subdir
>          0   003-file
> Inode not found.
>          0   004-link
> 
> Signed-off-by: Campbell Suter <campbell@snapit.group>
> Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>

Applied to u-boot/master, thanks!

-- 
Tom

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