[U-Boot] fat: handle paths that include ../

[Tom Rini]

On Tue, Jul 28, 2015 at 09:55:03PM -0600, Stephen Warren wrote:

> The FAT code contains a special case to parse the root directory. This
> is needed since the root directory location/layout on disk is special
> cased for FAT12/16. In particular, the location and size of the FAT12/16
> root directory is hard-coded and contiguous, whereas all FAT12/16 non-root
> directories, and all FAT32 directories, are stored in a non-contiguous
> fashion, with the layout represented by a linked-list of clusters in the
> FAT.
> 
> If a file path contains ../ (for example /extlinux/../bcm2835-rpi-cm.dtb),
> it is possible to need to parse the root directory for the first element
> in the path (requiring application of the special case), then a sub-
> directory (in the general way), then re-parse the root directory (again
> requiring the special case). However, the current code in U-Boot only
> applies the special case for the very first path element, and never for
> any later path element. When reparsing the root directory without
> applying the special case, any file in a sector (or cluster?) other than
> the first sector/cluster of the root directory will not be found.
> 
> This change modifies the non-root-dir-parsing loop of do_fat_read_at()
> to detect if it's walked back to the root directory, and if so, jumps
> back to the special case code that handles parsing of the root directory.
> 
> This change was tested using sandbox by executing:
> 
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/.."
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/../"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/../backup"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/../backup/"
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/../backup/.."
> ./u-boot -c "host bind 0 ../sd-p1.bin; ls host 0:0 /extlinux/../backup/../"
> ./u-boot -c "host bind 0 ../sd-p1.bin; load host 0:0 0 /bcm2835-rpi-cm.dtb"
> ./u-boot -c "host bind 0 ../sd-p1.bin; load host 0:0 0 /extlinux/../bcm2835-rpi-cm.dtb"
> ./u-boot -c "host bind 0 ../sd-p1.bin; load host 0:0 0 /backup/../bcm2835-rpi-cm.dtb"
> ./u-boot -c "host bind 0 ../sd-p1.bin; load host 0:0 0 /extlinux/..backup/../bcm2835-rpi-cm.dtb"
> ./u-boot -c "host bind 0 ../sd-p1.bin; load host 0:0 0 /extlinux/../backup/../bcm2835-rpi-cm.dtb"
> 
> (/extlinux and /backup are in different sectors so trigger some different
> cases, and bcm2835-rpi-cm.dtb is in a sector of the root directory other
> than the first).
> 
> In all honesty, this change is a bit of a hack, using goto and all.
> However, as demonstrated above it appears to work well in practice, is
> quite minimal, likely doesn't introduce any risk of regressions, and
> hopefully doesn't introduce any maintenance issues.
> 
> The correct fix would be to collapse the root and non-root loops in
> do_fat_read_at() and get_dentfromdir() into a single loop that has a
> small special-case when moving from one sector to the next, to handle
> the layout difference of root/non-root directories. AFAIK all other
> aspects of directory parsing are identical. However, that's a much
> larger change which needs significantly more thought before it's
> implemented.
> 
> Signed-off-by: Stephen Warren <swarren at wwwdotorg.org>

Applied to u-boot/master, thanks!

-- 
Tom
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