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Date: Fri, 1 May 2020 16:17:54 +0200
From: Mickaël Salaün <>
To: James Morris <>
Cc:, Aleksa Sarai <>,
 Alexei Starovoitov <>, Al Viro <>,
 Andy Lutomirski <>, Christian Heimes <>,
 Daniel Borkmann <>,
 Deven Bowers <>,
 Eric Chiang <>, Florian Weimer <>,
 Jan Kara <>, Jann Horn <>,
 Jonathan Corbet <>, Kees Cook <>,
 Matthew Garrett <>, Matthew Wilcox <>,
 Michael Kerrisk <>,
 Mickaël Salaün <>,
 Mimi Zohar <>,
 Philippe Trébuchet <>,
 Scott Shell <>,
 Sean Christopherson <>,
 Shuah Khan <>, Steve Dower <>,
 Steve Grubb <>,
 Thibaut Sautereau <>,
 Vincent Strubel <>,,,,
Subject: Re: [PATCH v3 2/5] fs: Add a MAY_EXECMOUNT flag to infer the noexec
 mount property

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
>> Signed-off-by: Mickaël Salaün <>
>> Reviewed-by: Philippe Trébuchet <>
>> Reviewed-by: Thibaut Sautereau <>
>> Cc: Aleksa Sarai <>
>> Cc: Al Viro <>
>> Cc: Kees Cook <>
> 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.

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