diff mbox series

[v2] dma-buf: Move dma_buf_release() from fops to dentry_ops

Message ID 20200611114418.19852-1-sumit.semwal@linaro.org
State Accepted
Commit 4ab59c3c638c6c8952bf07739805d20eb6358a4d
Headers show
Series [v2] dma-buf: Move dma_buf_release() from fops to dentry_ops | expand

Commit Message

Sumit Semwal June 11, 2020, 11:44 a.m. UTC 
Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which
happens if the dma_buf_release() is called while the userspace is
accessing the dma_buf pseudo fs's dmabuffs_dname() in another process,
and dma_buf_release() releases the dmabuf object when the last reference
to the struct file goes away.

I discussed with Arnd Bergmann, and he suggested that rather than tying
the dma_buf_release() to the file_operations' release(), we can tie it to
the dentry_operations' d_release(), which will be called when the last ref
to the dentry is removed.

The path exercised by __fput() calls f_op->release() first, and then calls
dput, which eventually calls d_op->d_release().

In the 'normal' case, when no userspace access is happening via dma_buf
pseudo fs, there should be exactly one fd, file, dentry and inode, so
closing the fd will kill of everything right away.

In the presented case, the dentry's d_release() will be called only when
the dentry's last ref is released.

Therefore, lets move dma_buf_release() from fops->release() to
d_ops->d_release()

Many thanks to Arnd for his FS insights :)

[1]: https://lore.kernel.org/patchwork/patch/1238278/

Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls")
Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com
Cc: <stable@vger.kernel.org> [5.3+]
Cc: Arnd Bergmann <arnd@arndb.de>
Reported-by: Charan Teja Reddy <charante@codeaurora.org>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>

Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>


---
v2: per Arnd: Moved dma_buf_release() above to avoid forward declaration;
     removed dentry_ops check.
---
 drivers/dma-buf/dma-buf.c | 54 ++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 29 deletions(-)

-- 
2.27.0

Comments

Sumit Semwal June 16, 2020, 12:42 p.m. UTC | #1 
Hello,

If there are no objections to this, I will plan to merge it soon.

Daniel, Chris, Chenbo?

On Thu, 11 Jun 2020 at 17:14, Sumit Semwal <sumit.semwal@linaro.org> wrote:
>

> Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which

> happens if the dma_buf_release() is called while the userspace is

> accessing the dma_buf pseudo fs's dmabuffs_dname() in another process,

> and dma_buf_release() releases the dmabuf object when the last reference

> to the struct file goes away.

>

> I discussed with Arnd Bergmann, and he suggested that rather than tying

> the dma_buf_release() to the file_operations' release(), we can tie it to

> the dentry_operations' d_release(), which will be called when the last ref

> to the dentry is removed.

>

> The path exercised by __fput() calls f_op->release() first, and then calls

> dput, which eventually calls d_op->d_release().

>

> In the 'normal' case, when no userspace access is happening via dma_buf

> pseudo fs, there should be exactly one fd, file, dentry and inode, so

> closing the fd will kill of everything right away.

>

> In the presented case, the dentry's d_release() will be called only when

> the dentry's last ref is released.

>

> Therefore, lets move dma_buf_release() from fops->release() to

> d_ops->d_release()

>

> Many thanks to Arnd for his FS insights :)

>

> [1]: https://lore.kernel.org/patchwork/patch/1238278/

>

> Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls")

> Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com

> Cc: <stable@vger.kernel.org> [5.3+]

> Cc: Arnd Bergmann <arnd@arndb.de>

> Reported-by: Charan Teja Reddy <charante@codeaurora.org>

> Reviewed-by: Arnd Bergmann <arnd@arndb.de>

> Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

>

> ---

> v2: per Arnd: Moved dma_buf_release() above to avoid forward declaration;

>      removed dentry_ops check.

> ---

>  drivers/dma-buf/dma-buf.c | 54 ++++++++++++++++++---------------------

>  1 file changed, 25 insertions(+), 29 deletions(-)

>

> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c

> index 01ce125f8e8d..412629601ad3 100644

> --- a/drivers/dma-buf/dma-buf.c

> +++ b/drivers/dma-buf/dma-buf.c

> @@ -54,37 +54,11 @@ static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)

>                              dentry->d_name.name, ret > 0 ? name : "");

>  }

>

> -static const struct dentry_operations dma_buf_dentry_ops = {

> -       .d_dname = dmabuffs_dname,

> -};

> -

> -static struct vfsmount *dma_buf_mnt;

> -

> -static int dma_buf_fs_init_context(struct fs_context *fc)

> -{

> -       struct pseudo_fs_context *ctx;

> -

> -       ctx = init_pseudo(fc, DMA_BUF_MAGIC);

> -       if (!ctx)

> -               return -ENOMEM;

> -       ctx->dops = &dma_buf_dentry_ops;

> -       return 0;

> -}

> -

> -static struct file_system_type dma_buf_fs_type = {

> -       .name = "dmabuf",

> -       .init_fs_context = dma_buf_fs_init_context,

> -       .kill_sb = kill_anon_super,

> -};

> -

> -static int dma_buf_release(struct inode *inode, struct file *file)

> +static void dma_buf_release(struct dentry *dentry)

>  {

>         struct dma_buf *dmabuf;

>

> -       if (!is_dma_buf_file(file))

> -               return -EINVAL;

> -

> -       dmabuf = file->private_data;

> +       dmabuf = dentry->d_fsdata;

>

>         BUG_ON(dmabuf->vmapping_counter);

>

> @@ -110,9 +84,32 @@ static int dma_buf_release(struct inode *inode, struct file *file)

>         module_put(dmabuf->owner);

>         kfree(dmabuf->name);

>         kfree(dmabuf);

> +}

> +

> +static const struct dentry_operations dma_buf_dentry_ops = {

> +       .d_dname = dmabuffs_dname,

> +       .d_release = dma_buf_release,

> +};

> +

> +static struct vfsmount *dma_buf_mnt;

> +

> +static int dma_buf_fs_init_context(struct fs_context *fc)

> +{

> +       struct pseudo_fs_context *ctx;

> +

> +       ctx = init_pseudo(fc, DMA_BUF_MAGIC);

> +       if (!ctx)

> +               return -ENOMEM;

> +       ctx->dops = &dma_buf_dentry_ops;

>         return 0;

>  }

>

> +static struct file_system_type dma_buf_fs_type = {

> +       .name = "dmabuf",

> +       .init_fs_context = dma_buf_fs_init_context,

> +       .kill_sb = kill_anon_super,

> +};

> +

>  static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)

>  {

>         struct dma_buf *dmabuf;

> @@ -412,7 +409,6 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)

>  }

>

>  static const struct file_operations dma_buf_fops = {

> -       .release        = dma_buf_release,

>         .mmap           = dma_buf_mmap_internal,

>         .llseek         = dma_buf_llseek,

>         .poll           = dma_buf_poll,

> --

> 2.27.0

>


Best,
Sumit.
Chris Wilson June 16, 2020, 12:50 p.m. UTC | #2 
Quoting Sumit Semwal (2020-06-16 13:42:13)
> Hello,
> 
> If there are no objections to this, I will plan to merge it soon.

I was going to suggest running it against our CI, but that's unavailable
at the moment.

There's a particularly nasty BUG_ON() in dma_buf_release that we hit
irregularly, that this might help with.
-Chris
Sumit Semwal June 22, 2020, 6:34 a.m. UTC | #3 
Hello Charan,

On Tue, 16 Jun 2020 at 19:13, Charan Teja Kalla <charante@codeaurora.org> wrote:
>

> Thanks Sumit for the fix.

>

> On 6/11/2020 5:14 PM, Sumit Semwal wrote:

> > Charan Teja reported a 'use-after-free' in dmabuffs_dname [1], which

> > happens if the dma_buf_release() is called while the userspace is

> > accessing the dma_buf pseudo fs's dmabuffs_dname() in another process,

> > and dma_buf_release() releases the dmabuf object when the last reference

> > to the struct file goes away.

> >

> > I discussed with Arnd Bergmann, and he suggested that rather than tying

> > the dma_buf_release() to the file_operations' release(), we can tie it to

> > the dentry_operations' d_release(), which will be called when the last ref

> > to the dentry is removed.

> >

> > The path exercised by __fput() calls f_op->release() first, and then calls

> > dput, which eventually calls d_op->d_release().

> >

> > In the 'normal' case, when no userspace access is happening via dma_buf

> > pseudo fs, there should be exactly one fd, file, dentry and inode, so

> > closing the fd will kill of everything right away.

> >

> > In the presented case, the dentry's d_release() will be called only when

> > the dentry's last ref is released.

> >

> > Therefore, lets move dma_buf_release() from fops->release() to

> > d_ops->d_release()

> >

> > Many thanks to Arnd for his FS insights :)

> >

> > [1]: https://lore.kernel.org/patchwork/patch/1238278/

> >

> > Fixes: bb2bb9030425 ("dma-buf: add DMA_BUF_SET_NAME ioctls")

> > Reported-by: syzbot+3643a18836bce555bff6@syzkaller.appspotmail.com

> > Cc: <stable@vger.kernel.org> [5.3+]

> > Cc: Arnd Bergmann <arnd@arndb.de>

> > Reported-by: Charan Teja Reddy <charante@codeaurora.org>

> > Reviewed-by: Arnd Bergmann <arnd@arndb.de>

> > Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>

> >

>

> Tested this patch for Android running on Snapdragon hardware and see no

> issues.

> Tested-by: Charan Teja Reddy <charante@codeaurora.org>

Thanks for your tested-by, appreciate it!

Chris,
any luck with your CI to test if this also helps your
dma_buf_release() bug that you guys have seen?

If you've not been able to test, and there are no more objections by
EOD today, I will merge this to the drm-misc-fixes branch.

>

> > ---

> > v2: per Arnd: Moved dma_buf_release() above to avoid forward declaration;

> >      removed dentry_ops check.

> > ---


<snip>
Best,
Sumit.
diff mbox series

Patch

diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 01ce125f8e8d..412629601ad3 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -54,37 +54,11 @@  static char *dmabuffs_dname(struct dentry *dentry, char *buffer, int buflen)
 			     dentry->d_name.name, ret > 0 ? name : "");
 }
 
-static const struct dentry_operations dma_buf_dentry_ops = {
-	.d_dname = dmabuffs_dname,
-};
-
-static struct vfsmount *dma_buf_mnt;
-
-static int dma_buf_fs_init_context(struct fs_context *fc)
-{
-	struct pseudo_fs_context *ctx;
-
-	ctx = init_pseudo(fc, DMA_BUF_MAGIC);
-	if (!ctx)
-		return -ENOMEM;
-	ctx->dops = &dma_buf_dentry_ops;
-	return 0;
-}
-
-static struct file_system_type dma_buf_fs_type = {
-	.name = "dmabuf",
-	.init_fs_context = dma_buf_fs_init_context,
-	.kill_sb = kill_anon_super,
-};
-
-static int dma_buf_release(struct inode *inode, struct file *file)
+static void dma_buf_release(struct dentry *dentry)
 {
 	struct dma_buf *dmabuf;
 
-	if (!is_dma_buf_file(file))
-		return -EINVAL;
-
-	dmabuf = file->private_data;
+	dmabuf = dentry->d_fsdata;
 
 	BUG_ON(dmabuf->vmapping_counter);
 
@@ -110,9 +84,32 @@  static int dma_buf_release(struct inode *inode, struct file *file)
 	module_put(dmabuf->owner);
 	kfree(dmabuf->name);
 	kfree(dmabuf);
+}
+
+static const struct dentry_operations dma_buf_dentry_ops = {
+	.d_dname = dmabuffs_dname,
+	.d_release = dma_buf_release,
+};
+
+static struct vfsmount *dma_buf_mnt;
+
+static int dma_buf_fs_init_context(struct fs_context *fc)
+{
+	struct pseudo_fs_context *ctx;
+
+	ctx = init_pseudo(fc, DMA_BUF_MAGIC);
+	if (!ctx)
+		return -ENOMEM;
+	ctx->dops = &dma_buf_dentry_ops;
 	return 0;
 }
 
+static struct file_system_type dma_buf_fs_type = {
+	.name = "dmabuf",
+	.init_fs_context = dma_buf_fs_init_context,
+	.kill_sb = kill_anon_super,
+};
+
 static int dma_buf_mmap_internal(struct file *file, struct vm_area_struct *vma)
 {
 	struct dma_buf *dmabuf;
@@ -412,7 +409,6 @@  static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file)
 }
 
 static const struct file_operations dma_buf_fops = {
-	.release	= dma_buf_release,
 	.mmap		= dma_buf_mmap_internal,
 	.llseek		= dma_buf_llseek,
 	.poll		= dma_buf_poll,