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: [email protected]
Cc: <[email protected]> [5.3+]
Cc: Arnd Bergmann <[email protected]>
Reported-by: Charan Teja Reddy <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Sumit Semwal <[email protected]>
---
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
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 <[email protected]> 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: [email protected]
> Cc: <[email protected]> [5.3+]
> Cc: Arnd Bergmann <[email protected]>
> Reported-by: Charan Teja Reddy <[email protected]>
> Reviewed-by: Arnd Bergmann <[email protected]>
> Signed-off-by: Sumit Semwal <[email protected]>
>
> ---
> 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.
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
Hi Chris,
On Tue, 16 Jun 2020 at 18:20, Chris Wilson <[email protected]> wrote:
>
> 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.
Thanks for your reply; if the CI is going to be available in a couple
of days, we could wait - it'd be definitely good to see a bug being
splattered out!
> -Chris
Best,
Sumit.
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: [email protected]
> Cc: <[email protected]> [5.3+]
> Cc: Arnd Bergmann <[email protected]>
> Reported-by: Charan Teja Reddy <[email protected]>
> Reviewed-by: Arnd Bergmann <[email protected]>
> Signed-off-by: Sumit Semwal <[email protected]>
>
Tested this patch for Android running on Snapdragon hardware and see no
issues.
Tested-by: Charan Teja Reddy <[email protected]>
> ---
> 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,
>
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora
Forum, a Linux Foundation Collaborative Project
Hello Charan,
On Tue, 16 Jun 2020 at 19:13, Charan Teja Kalla <[email protected]> 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: [email protected]
> > Cc: <[email protected]> [5.3+]
> > Cc: Arnd Bergmann <[email protected]>
> > Reported-by: Charan Teja Reddy <[email protected]>
> > Reviewed-by: Arnd Bergmann <[email protected]>
> > Signed-off-by: Sumit Semwal <[email protected]>
> >
>
> Tested this patch for Android running on Snapdragon hardware and see no
> issues.
> Tested-by: Charan Teja Reddy <[email protected]>
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.