Re: [PATCH v22 07/12] landlock: Support filesystem access-control

Mickaël Salaün
2020-11-03T16:03:53Z

On 29/10/2020 02:06, Jann Horn wrote:
> (On Tue, Oct 27, 2020 at 9:04 PM Mickaël Salaün <mic@digikod.net> wrote:

>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> [...]
>> +static inline u32 get_file_access(const struct file *const file)
>> +{
>> + u32 access = 0;
>> +
>> + if (file->f_mode & FMODE_READ) {
>> + /* A directory can only be opened in read mode. */
>> + if (S_ISDIR(file_inode(file)->i_mode))
>> + return LANDLOCK_ACCESS_FS_READ_DIR;
>> + access = LANDLOCK_ACCESS_FS_READ_FILE;
>> + }
>> + /*
>> + * A LANDLOCK_ACCESS_FS_APPEND could be added but we also need to check
>> + * fcntl(2).
>> + */
>
> Once https://lore.kernel.org/linux-api/20200831153207.GO3265@brightrain.aerifal.cx/
> lands, pwritev2() with RWF_NOAPPEND will also be problematic for
> classifying "write" vs "append"; you may want to include that in the
> comment. (Or delete the comment.)

Contrary to fcntl(2), pwritev2(2) doesn't seems to modify the file
description. Otherwise, other LSMs would need to be patched.
I'll remove this comment anyway.

>
>> + if (file->f_mode & FMODE_WRITE)
>> + access |= LANDLOCK_ACCESS_FS_WRITE_FILE;
>> + /* __FMODE_EXEC is indeed part of f_flags, not f_mode. */
>> + if (file->f_flags & __FMODE_EXEC)
>> + access |= LANDLOCK_ACCESS_FS_EXECUTE;
>> + return access;
>> +}
> [...]
>