[PATCH] setns.2: fix CLONE_NEWNS restriction info

[PATCH] setns.2: fix CLONE_NEWNS restriction info

[Mike Frysinger]

Threads are allowed to switch mount namespaces if the filesystem
details aren't being shared.  That's the purpose of the check in
the kernel quoted by the comment:
    if (fs->users != 1)
        return -EINVAL;

It's been this way since the code was originally merged in v3.8.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
---
 man2/setns.2 | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/man2/setns.2 b/man2/setns.2
index 18e80202326a..5985c099b464 100644
--- a/man2/setns.2
+++ b/man2/setns.2
@@ -131,8 +131,12 @@ capabilities in its own user namespace and
 .BR CAP_SYS_ADMIN
 in the user namespace that owns the target mount namespace.
 .IP
-A process may not be reassociated with a new mount namespace if it is
-multithreaded.
+A process can't join a new mount namespace if it is sharing
+filesystem-related attributes
+(the attributes whose sharing is controlled by the
+.BR clone (2)
+.B CLONE_FS
+flag) with another process.
 .\" Above check is in fs/namespace.c:mntns_install() [3.8 source]
 .IP
 See
-- 
2.23.0

Re: [PATCH] setns.2: fix CLONE_NEWNS restriction info

[Michael Kerrisk (man-pages)]

Hello Mike,

On 9/19/19 7:43 AM, Mike Frysinger wrote:
> Threads are allowed to switch mount namespaces if the filesystem
> details aren't being shared.  That's the purpose of the check in
> the kernel quoted by the comment:
>     if (fs->users != 1)
>         return -EINVAL;
> 
> It's been this way since the code was originally merged in v3.8.

Thanks. Patch applied.

Cheers,

Michael

> Signed-off-by: Mike Frysinger <vapier@gentoo.org>
> ---
>  man2/setns.2 | 8 ++++++--
>  1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/man2/setns.2 b/man2/setns.2
> index 18e80202326a..5985c099b464 100644
> --- a/man2/setns.2
> +++ b/man2/setns.2
> @@ -131,8 +131,12 @@ capabilities in its own user namespace and
>  .BR CAP_SYS_ADMIN
>  in the user namespace that owns the target mount namespace.
>  .IP
> -A process may not be reassociated with a new mount namespace if it is
> -multithreaded.
> +A process can't join a new mount namespace if it is sharing
> +filesystem-related attributes
> +(the attributes whose sharing is controlled by the
> +.BR clone (2)
> +.B CLONE_FS
> +flag) with another process.
>  .\" Above check is in fs/namespace.c:mntns_install() [3.8 source]
>  .IP
>  See
> 


-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/