[PATCH v6 5/7] fs,doc: Enable to enforce noexec mounts or file exec through O_MAYEXEC

[Mickaël Salaün]

On 14/07/2020 20:40, Randy Dunlap wrote:
> Hi,
> 
> On 7/14/20 11:16 AM, Mickaël Salaün wrote:
> 
>> ---
>>  Documentation/admin-guide/sysctl/fs.rst | 45 +++++++++++++++++++++++++
>>  fs/namei.c                              | 29 +++++++++++++---
>>  include/linux/fs.h                      |  1 +
>>  kernel/sysctl.c                         | 12 +++++--
>>  4 files changed, 80 insertions(+), 7 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst
>> index 2a45119e3331..02ec384b8bbf 100644
>> --- a/Documentation/admin-guide/sysctl/fs.rst
>> +++ b/Documentation/admin-guide/sysctl/fs.rst
> 
> Reviewed-by: Randy Dunlap <rdunlap at infradead.org>
> 
> with one tiny nit:
> 
>> @@ -165,6 +166,50 @@ system needs to prune the inode list instead of allocating
>> +The ability to restrict code execution must be thought as a system-wide policy,
>> +which first starts by restricting mount points with the ``noexec`` option.
>> +This option is also automatically applied to special filesystems such as /proc
>> +.  This prevents files on such mount points to be directly executed by the
> 
> Can you move that period from the beginning of the line to the end of the
> previous line?

OK, done. Thanks!

> 
>> +kernel or mapped as executable memory (e.g. libraries).  With script
>> +interpreters using the ``O_MAYEXEC`` flag, the executable permission can then
>> +be checked before reading commands from files. This makes it possible to
>> +enforce the ``noexec`` at the interpreter level, and thus propagates this
>> +security policy to scripts.  To be fully effective, these interpreters also
>> +need to handle the other ways to execute code: command line parameters (e.g.,
>> +option ``-e`` for Perl), module loading (e.g., option ``-m`` for Python),
>> +stdin, file sourcing, environment variables, configuration files, etc.
>> +According to the threat model, it may be acceptable to allow some script
>> +interpreters (e.g. Bash) to interpret commands from stdin, may it be a TTY or a
>> +pipe, because it may not be enough to (directly) perform syscalls.
> 
> thanks.
>