[U-Boot] [PATCH] ext4: fix possible crash on directory traversal, ignore deleted entries

[Tom Rini <trini@konsulko.com>]

On Sun, Aug 28, 2016 at 09:44:41PM +0200, Stefan Bruens wrote:
> On Freitag, 19. August 2016 15:54:51 CEST you wrote:
> > On Sun, Aug 14, 2016 at 05:11:04AM +0200, Stefan Br?ns wrote:
> > > The following command triggers a segfault in search_dir:
> > > ./sandbox/u-boot -c 'host bind 0 ./sandbox/test/fs/3GB.ext4.img ;
> > > 
> > >     ext4write host 0 0 /./foo 0x10'
> > > 
> > > The following command triggers a segfault in check_filename:
> > > ./sandbox/u-boot -c 'host bind 0 ./sandbox/test/fs/3GB.ext4.img ;
> > > 
> > >     ext4write host 0 0 /. 0x10'
> > > 
> > > "." is the first entry in the directory, thus previous_dir is NULL. The
> > > whole previous_dir block in search_dir seems to be a bad copy from
> > > check_filename(...). As the changed data is not written to disk, the
> > > statement is mostly harmless, save the possible NULL-ptr reference.
> > > 
> > > Typically a file is unlinked by extending the direntlen of the previous
> > > entry. If the entry is the first entry in the directory block, it is
> > > invalidated by setting inode=0.
> > > 
> > > The inode==0 case is hard to trigger without crafted filesystems. It only
> > > hits if the first entry in a directory block is deleted and later a lookup
> > > for the entry (by name) is done.
> > > 
> > > Signed-off-by: Stefan Br?ns <stefan.bruens@rwth-aachen.de>
> > > ---
> > > 
> > >  fs/ext4/ext4_common.c | 57
> > >  ++++++++++++++++++--------------------------------- fs/ext4/ext4_write.c
> > >   |  2 +-
> > >  include/ext4fs.h      |  2 +-
> > >  3 files changed, 22 insertions(+), 39 deletions(-)
> > 
> > Can you please add the test case to the existing scripts?  Thanks!
> 
> Adding this to the current test script is somewhat problematic. The test runs 
> all tests for fat and ext4, so each testcase should be file system agnostic. 
> Unfortunately fat and ext4 (at least as implemented in U-Boot) have different 
> semantics, as ext4 in U-Boot requires all path to absolute paths, whereas fat 
> seems to require something else (relative path? absolute path, but without 
> leading '/'?).
> 
> Calling 'fatwrite host 0 0 /. 0x10' happily creates a directory! called '/.', 
> 'fatwrite host 0 0 /./foo 0x10' creates a file and copletely messes up the 
> filesystem (according to fsck.vfat and mounting the fs in linux).
> 
> Any advise?

Can we fix this up in the argument parsing?  This sounds like it's
showing some bugs in the fatwrite parsing code itself.

-- 
Tom
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