Re: [PATCH v2] vfat: don't read garbage after last dirent

From: OGAWA Hirofumi
Date: Mon Dec 24 2018 - 07:14:59 EST

Matteo Croce <mcroce@xxxxxxxxxx> writes:

> The FAT32 File System Specification[1] states that:
> If DIR_Name[0] == 0x00, then the directory entry is free, and there
> are no allocated directory entries after this one.
> The special 0 value, indicates to FAT file system driver code that
> the rest of the entries in this directory do not need to be examined
> because they are all free.
> This is not enforced by Linux, and is possible to read garbage if not
> all dirents after the last one are filled with zeroes.
> [1]
> Reported-by: Timothy Redaelli <tredaelli@xxxxxxxxxx>
> Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxx>

We have to handle all paths that is using fat_get_entry(), to make
consistent behavior.

With quick check, there are still several issues remaining. Please check
more. For example, looks like fat_parse_long()/fat_search_long() path is
missing, and fat_get_dotdot_entry(), fat_subdirs() too.

(while adding new entry, if we found zeroed entry, we would be better to
warn about fsck.)

OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx>