[PATCH] vfs: reorder checks in may_create_in_sticky

[PATCH] vfs: reorder checks in may_create_in_sticky

[Mateusz Guzik]

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@gmail.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;
-- 
2.43.0

Re: [PATCH] vfs: reorder checks in may_create_in_sticky

[Jan Kara]

On Thu 20-06-24 14:03:59, 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@gmail.com>

Yeah, putting the sticky bit check first makes sense also logically. Feel
free to add:

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

								Honza

> ---
>  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;
> -- 
> 2.43.0
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

Re: [PATCH] vfs: reorder checks in may_create_in_sticky

[Christian Brauner]

On Thu, 20 Jun 2024 14:03:59 +0200, 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.
> 
> [...]

The list of checks is unspeakably irritating. I really dislike looking at this
function.

---

Applied to the vfs.misc branch of the vfs/vfs.git tree.
Patches in the vfs.misc branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.misc

[1/1] vfs: reorder checks in may_create_in_sticky
      https://git.kernel.org/vfs/vfs/c/6cc620b3a050

Re: [PATCH] vfs: reorder checks in may_create_in_sticky

[Christian Brauner]

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@gmail.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?

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;
 }

That gives us:

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, 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 (vfsuid_eq_kuid(i_vfsuid, current_fsuid()))
		return 0;

	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;
}

Re: [PATCH] vfs: reorder checks in may_create_in_sticky

[Mateusz Guzik]

On Fri, Jun 21, 2024 at 9:45 AM Christian Brauner <brauner@kernel.org> 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@gmail.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?
>
> 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;
>  }
>
> That gives us:
>
> 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, 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 (vfsuid_eq_kuid(i_vfsuid, current_fsuid()))
>                 return 0;
>
>         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;
> }

That does look better. :)

So as far as I'm concerned my patch can be just dropped, just in case
I'll note there is no need to mention me anywhere near this.

-- 
Mateusz Guzik <mjguzik gmail.com>

Re: [PATCH] vfs: reorder checks in may_create_in_sticky

[Jan Kara]

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@gmail.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@suse.cz>

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