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

[Mickaël Salaün]

On 29/10/2020 02:06, Jann Horn wrote:
> (On Tue, Oct 27, 2020 at 9:04 PM Mickaël Salaün <mic@xxxxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxx/
> 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;
>> +}
> [...]
>