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ext4: fix possible crash on directory traversal, ignore deleted entries

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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 Brüns <stefan.bruens@rwth-aachen.de>
Reviewed-by: Lukasz Majewski <l.majewski@samsung.com>
This commit is contained in:
Stefan Brüns
2016-09-06 04:36:41 +02:00
committed by Tom Rini
parent 011bc3342a
commit 76a29519ff
3 changed files with 23 additions and 39 deletions
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2
fs/ext4/ext4_write.c
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@@ -882,7 +882,7 @@ int ext4fs_write(const char *fname, unsigned char *buffer,
if (ext4fs_iget(parent_inodeno, g_parent_inode))
goto fail;
/* check if the filename is already present in root */
existing_file_inodeno = ext4fs_filename_check(filename);
existing_file_inodeno = ext4fs_filename_unlink(filename);
if (existing_file_inodeno != -1) {
ret = ext4fs_delete_file(existing_file_inodeno);
fs->first_pass_bbmap = 0;