[PATCH] cifs: verify that tcon is valid before dereference in cifs_kill_sb

[PATCH] cifs: verify that tcon is valid before dereference in cifs_kill_sb

[Ronnie Sahlberg]

On umount, cifs_sb->tlink_tree might contain entries that do not represent
a valid tcon.
Check the tcon for error before we dereference it.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
---
 fs/cifs/cifsfs.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index aba0783a8f09..25719b70564a 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_block *sb)
 	 * before we kill the sb.
 	 */
 	if (cifs_sb->root) {
-		node = rb_first(root);
-		while (node != NULL) {
+		for(node = rb_first(root); node; node = rb_next(node)) {
 			tlink = rb_entry(node, struct tcon_link, tl_rbnode);
 			tcon = tlink_tcon(tlink);
+			if (IS_ERR(tcon))
+				continue;
 			cfid = &tcon->crfid;
 			mutex_lock(&cfid->fid_mutex);
 			if (cfid->dentry) {
@@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_block *sb)
 				cfid->dentry = NULL;
 			}
 			mutex_unlock(&cfid->fid_mutex);
-			node = rb_next(node);
 		}
 
 		/* finally release root dentry */
-- 
2.30.2

Re: [PATCH] cifs: verify that tcon is valid before dereference in cifs_kill_sb

[Shyam Prasad N]

On Wed, Apr 13, 2022 at 7:06 AM Ronnie Sahlberg <lsahlber@redhat.com> wrote:
>
> On umount, cifs_sb->tlink_tree might contain entries that do not represent
> a valid tcon.
> Check the tcon for error before we dereference it.
>
> Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> ---
>  fs/cifs/cifsfs.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> index aba0783a8f09..25719b70564a 100644
> --- a/fs/cifs/cifsfs.c
> +++ b/fs/cifs/cifsfs.c
> @@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_block *sb)
>          * before we kill the sb.
>          */
>         if (cifs_sb->root) {
> -               node = rb_first(root);
> -               while (node != NULL) {
> +               for(node = rb_first(root); node; node = rb_next(node)) {
>                         tlink = rb_entry(node, struct tcon_link, tl_rbnode);
>                         tcon = tlink_tcon(tlink);
> +                       if (IS_ERR(tcon))
> +                               continue;
>                         cfid = &tcon->crfid;
>                         mutex_lock(&cfid->fid_mutex);
>                         if (cfid->dentry) {
> @@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_block *sb)
>                                 cfid->dentry = NULL;
>                         }
>                         mutex_unlock(&cfid->fid_mutex);
> -                       node = rb_next(node);
>                 }
>
>                 /* finally release root dentry */
> --
> 2.30.2
>

The changes look good to me.
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>

Does this cover all the mount failure scenarios, Ronnie?

-- 
Regards,
Shyam

Re: [PATCH] cifs: verify that tcon is valid before dereference in cifs_kill_sb

[ronnie sahlberg]

On Thu, Apr 14, 2022 at 11:33 PM Shyam Prasad N <nspmangalore@gmail.com> wrote:
>
> On Wed, Apr 13, 2022 at 7:06 AM Ronnie Sahlberg <lsahlber@redhat.com> wrote:
> >
> > On umount, cifs_sb->tlink_tree might contain entries that do not represent
> > a valid tcon.
> > Check the tcon for error before we dereference it.
> >
> > Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
> > ---
> >  fs/cifs/cifsfs.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
> > index aba0783a8f09..25719b70564a 100644
> > --- a/fs/cifs/cifsfs.c
> > +++ b/fs/cifs/cifsfs.c
> > @@ -266,10 +266,11 @@ static void cifs_kill_sb(struct super_block *sb)
> >          * before we kill the sb.
> >          */
> >         if (cifs_sb->root) {
> > -               node = rb_first(root);
> > -               while (node != NULL) {
> > +               for(node = rb_first(root); node; node = rb_next(node)) {
> >                         tlink = rb_entry(node, struct tcon_link, tl_rbnode);
> >                         tcon = tlink_tcon(tlink);
> > +                       if (IS_ERR(tcon))
> > +                               continue;
> >                         cfid = &tcon->crfid;
> >                         mutex_lock(&cfid->fid_mutex);
> >                         if (cfid->dentry) {
> > @@ -277,7 +278,6 @@ static void cifs_kill_sb(struct super_block *sb)
> >                                 cfid->dentry = NULL;
> >                         }
> >                         mutex_unlock(&cfid->fid_mutex);
> > -                       node = rb_next(node);
> >                 }
> >
> >                 /* finally release root dentry */
> > --
> > 2.30.2
> >
>
> The changes look good to me.
> Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
>
> Does this cover all the mount failure scenarios, Ronnie?

It should. It should also fix similar issues at umount if an idle tcon
has been reaped, or say a tcon failed to initialize during multiuser.
For example, mount multiuser, then try to access the share with a
different user without credentials. That second tcon will fail
and then when we umount we would oops.

>
> --
> Regards,
> Shyam