[PATCH] ovl: inode reference leak in "ovl_is_inuse" true case.

[PATCH] ovl: inode reference leak in "ovl_is_inuse" true case.

[youngjun]

When "ovl_is_inuse" true case, trap inode reference not put.

Signed-off-by: youngjun <her0gyugyu@gmail.com>
---
 fs/overlayfs/super.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 91476bc422f9..8837fc1ec3be 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1499,8 +1499,10 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 
 		if (ovl_is_inuse(stack[i].dentry)) {
 			err = ovl_report_in_use(ofs, "lowerdir");
-			if (err)
+			if (err) {
+				iput(trap);
 				goto out;
+			}
 		}
 
 		mnt = clone_private_mount(&stack[i]);
-- 
2.17.1

Re: [PATCH] ovl: inode reference leak in "ovl_is_inuse" true case.

[Amir Goldstein]

On Mon, Jun 15, 2020 at 6:57 PM youngjun <her0gyugyu@gmail.com> wrote:
>
> When "ovl_is_inuse" true case, trap inode reference not put.
>
> Signed-off-by: youngjun <her0gyugyu@gmail.com>

Fixes: 0be0bfd2de9d ("ovl: fix regression caused by overlapping layers
detection")
Cc: <stable@vger.kernel.org> # v4.19+
Reviewed-by: Amir Goldstein <amir73il@gmail.com>


> ---
>  fs/overlayfs/super.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 91476bc422f9..8837fc1ec3be 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1499,8 +1499,10 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
>
>                 if (ovl_is_inuse(stack[i].dentry)) {
>                         err = ovl_report_in_use(ofs, "lowerdir");
> -                       if (err)
> +                       if (err) {
> +                               iput(trap);
>                                 goto out;
> +                       }
>                 }
>

Urgh! I moved this ovl_is_inuse() after ovl_setup_trap() for a reason, but I did
not explain why. While we are fixing the bug, it would be nice to add a comment
above ovl_setup_trap():

/*
 * Check if lower root conflicts with this overlay layers before checking
 * if it is in-use as upperdir/workdir of "another" mount, because we do
 * not bother to check in ovl_is_inuse() if the upperdir/workdir is in fact
 * in-use by our upperdir/workdir.
 */

Thanks,
Amir.

[PATCH] ovl: inode reference leak in ovl_is_inuse true case.

[youngjun]

When "ovl_is_inuse" true case, trap inode reference not put.
plus adding the comment explaining sequence of
ovl_is_inuse after ovl_setup_trap.

Signed-off-by: youngjun <her0gyugyu@gmail.com>
---
 fs/overlayfs/super.c | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 91476bc422f9..0396793dadb8 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1029,6 +1029,12 @@ static const struct xattr_handler *ovl_xattr_handlers[] = {
 	NULL
 };
 
+/*
+ * Check if lower root conflicts with this overlay layers before checking
+ * if it is in-use as upperdir/workdir of "another" mount, because we do
+ * not bother to check in ovl_is_inuse() if the upperdir/workdir is in fact
+ * in-use by our upperdir/workdir.
+ */
 static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
 			  struct inode **ptrap, const char *name)
 {
@@ -1499,8 +1505,10 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
 
 		if (ovl_is_inuse(stack[i].dentry)) {
 			err = ovl_report_in_use(ofs, "lowerdir");
-			if (err)
+			if (err) {
+				iput(trap);
 				goto out;
+			}
 		}
 
 		mnt = clone_private_mount(&stack[i]);
-- 
2.17.1

Thank you for comment Amir. I modified patch as you said.

Re: [PATCH] ovl: inode reference leak in ovl_is_inuse true case.

[Amir Goldstein]

Hi youngjun!

Thank you for your patch.
You asked for guidance about posting patch revisions so let me repeat
my comment in a more clear way (see below).


On Tue, Jun 16, 2020 at 7:46 AM youngjun <her0gyugyu@gmail.com> wrote:
>

When posting a revision of a patch already posted, the practice
is to use the subject prefix [PATCH v2].
This will be auto generated for you with -v option for git format-patch.

Also, it is not valuable to CC LKML on patches with such a narrow
scope. The only relevant CC for this patch is the overlayfs list,
overlayfs maintainer and developers that reviewed v1 (me in that case).

> When "ovl_is_inuse" true case, trap inode reference not put.
> plus adding the comment explaining sequence of
> ovl_is_inuse after ovl_setup_trap.
>

Please add these lines to the bottom of commit message:
(They help the stable tree maintainers know that patch
 should be picked up and to which stable tree)

Fixes: 0be0bfd2de9d ("ovl: fix regression caused by overlapping layers..")
Cc: <stable@vger.kernel.org> # v4.19+
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: youngjun <her0gyugyu@gmail.com>
> ---
>  fs/overlayfs/super.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 91476bc422f9..0396793dadb8 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1029,6 +1029,12 @@ static const struct xattr_handler *ovl_xattr_handlers[] = {
>         NULL
>  };
>
> +/*
> + * Check if lower root conflicts with this overlay layers before checking
> + * if it is in-use as upperdir/workdir of "another" mount, because we do
> + * not bother to check in ovl_is_inuse() if the upperdir/workdir is in fact
> + * in-use by our upperdir/workdir.
> + */

Sorry for not being clear about this comment.
I meant it should come before the call to ovl_setup_trap() in
ovl_get_layers(). It is not true in general that we always call ovl_setup_trap()
before ovl_is_inuse(). It is only true and relevant for checking lower layers.

If anything I wrote is not clear, do not hesitate to ask for more clarification.

Thanks,
Amir.