Re: [PATCH v3 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec mount property

[MickaÃl SalaÃn]

On 01/05/2020 06:02, James Morris wrote:
> On Tue, 28 Apr 2020, Mickaël Salaün wrote:
> 
>> An LSM doesn't get path information related to an access request to open
>> an inode.  This new (internal) MAY_EXECMOUNT flag enables an LSM to
>> check if the underlying mount point of an inode is marked as executable.
>> This is useful to implement a security policy taking advantage of the
>> noexec mount option.
>>
>> This flag is set according to path_noexec(), which checks if a mount
>> point is mounted with MNT_NOEXEC or if the underlying superblock is
>> SB_I_NOEXEC.
>>
>> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxx>
>> Reviewed-by: Philippe Trébuchet <philippe.trebuchet@xxxxxxxxxxx>
>> Reviewed-by: Thibaut Sautereau <thibaut.sautereau@xxxxxxxxxxx>
>> Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
>> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
>> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> 
> Are there any existing LSMs which plan to use this aspect?

This commit message was initially for the first version of O_MAYEXEC,
which extended Yama. The current enforcement implementation is now
directly in the FS subsystem (as requested by Kees Cook). However, this
MAY_EXECMOUNT flag is still used by the current FS implementation and it
could still be useful for LSMs.