linux-kernel - Re: [PATCH] vfs: reorder checks in may_create_in

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Date: Fri, 21 Jun 2024 13:25:19 +0200
From: Jan Kara <jack@...e.cz>
To: Christian Brauner <brauner@...nel.org>
Cc: Mateusz Guzik <mjguzik@...il.com>, viro@...iv.linux.org.uk,
	jack@...e.cz, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH] vfs: reorder checks in may_create_in_sticky

On Fri 21-06-24 09:45:03, Christian Brauner wrote:
> On Thu, Jun 20, 2024 at 02:03:59PM GMT, Mateusz Guzik wrote:
> > The routine is called for all directories on file creation and weirdly
> > postpones the check if the dir is sticky to begin with. Instead it first
> > checks fifos and regular files (in that order), while avoidably pulling
> > globals.
> > 
> > No functional changes.
> > 
> > Signed-off-by: Mateusz Guzik <mjguzik@...il.com>
> > ---
> >  fs/namei.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > diff --git a/fs/namei.c b/fs/namei.c
> > index 63d1fb06da6b..b1600060ecfb 100644
> > --- a/fs/namei.c
> > +++ b/fs/namei.c
> > @@ -1246,9 +1246,9 @@ static int may_create_in_sticky(struct mnt_idmap *idmap,
> >  	umode_t dir_mode = nd->dir_mode;
> >  	vfsuid_t dir_vfsuid = nd->dir_vfsuid;
> >  
> > -	if ((!sysctl_protected_fifos && S_ISFIFO(inode->i_mode)) ||
> > -	    (!sysctl_protected_regular && S_ISREG(inode->i_mode)) ||
> > -	    likely(!(dir_mode & S_ISVTX)) ||
> > +	if (likely(!(dir_mode & S_ISVTX)) ||
> > +	    (S_ISREG(inode->i_mode) && !sysctl_protected_regular) ||
> > +	    (S_ISFIFO(inode->i_mode) && !sysctl_protected_fifos) ||
> >  	    vfsuid_eq(i_uid_into_vfsuid(idmap, inode), dir_vfsuid) ||
> >  	    vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode), current_fsuid()))
> >  		return 0;
> 
> I think we really need to unroll this unoly mess to make it more readable?

I guess my neural network has adapted to these kind of things in the kernel :)

> diff --git a/fs/namei.c b/fs/namei.c
> index 3e23fbb8b029..1dd2d328bae3 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -1244,25 +1244,43 @@ static int may_create_in_sticky(struct mnt_idmap *idmap,
>                                 struct nameidata *nd, struct inode *const inode)
>  {
>         umode_t dir_mode = nd->dir_mode;
> -       vfsuid_t dir_vfsuid = nd->dir_vfsuid;
> +       vfsuid_t dir_vfsuid = nd->dir_vfsuid, i_vfsuid;
> +       int ret;
> +
> +       if (likely(!(dir_mode & S_ISVTX)))
> +               return 0;
> +
> +       if (S_ISREG(inode->i_mode) && !sysctl_protected_regular)
> +               return 0;
> +
> +       if (S_ISFIFO(inode->i_mode) && !sysctl_protected_fifos)
> +               return 0;
> +
> +       i_vfsuid = i_uid_into_vfsuid(idmap, inode);
> +
> +       if (vfsuid_eq(i_vfsuid, dir_vfsuid))
> +               return 0;
> 
> -       if (likely(!(dir_mode & S_ISVTX)) ||
> -           (S_ISREG(inode->i_mode) && !sysctl_protected_regular) ||
> -           (S_ISFIFO(inode->i_mode) && !sysctl_protected_fifos) ||
> -           vfsuid_eq(i_uid_into_vfsuid(idmap, inode), dir_vfsuid) ||
> -           vfsuid_eq_kuid(i_uid_into_vfsuid(idmap, inode), current_fsuid()))
> +       if (vfsuid_eq_kuid(i_vfsuid, current_fsuid()))
>                 return 0;
> 
> -       if (likely(dir_mode & 0002) ||
> -           (dir_mode & 0020 &&
> -            ((sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) ||
> -             (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode))))) {
> -               const char *operation = S_ISFIFO(inode->i_mode) ?
> -                                       "sticky_create_fifo" :
> -                                       "sticky_create_regular";
> -               audit_log_path_denied(AUDIT_ANOM_CREAT, operation);
> +       if (likely(dir_mode & 0002)) {
> +               audit_log_path_denied(AUDIT_ANOM_CREAT, "sticky_create");
>                 return -EACCES;
>         }
> +
> +       if (dir_mode & 0020) {
> +               if (sysctl_protected_fifos >= 2 && S_ISFIFO(inode->i_mode)) {
> +                       audit_log_path_denied(AUDIT_ANOM_CREAT, "sticky_create_fifo");
> +                       return -EACCES;
> +               }
> +
> +               if (sysctl_protected_regular >= 2 && S_ISREG(inode->i_mode)) {
> +                       audit_log_path_denied(AUDIT_ANOM_CREAT, "sticky_create_regular");
> +                       return -EACCES;
> +               }
> +       }
> +
>         return 0;
>  }

But this definitely looks nicer to read... Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR