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Commit c06d3f2e authored by Charan Teja Reddy's avatar Charan Teja Reddy Committed by Gerrit - the friendly Code Review server
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dmabuf: fix use-after-free of dmabuf's file->f_inode 



It is observed 'use-after-free' on the dmabuf's file->f_inode with the
race between closing the dmabuf file and reading the dmabuf's debug
info.

Consider the below scenario where P1 is closing the dma_buf file
and P2 is reading the dma_buf's debug info in the system:

P1						P2
					dma_buf_debug_show()
dma_buf_put()
  __fput()
    file->f_op->release()
    dput()
    ....
      dentry_unlink_inode()
        iput(dentry->d_inode)
        (where the inode is freed)
					mutex_lock(&db_list.lock)
					read 'dma_buf->file->f_inode'
					(the same inode is freed by P1)
					mutex_unlock(&db_list.lock)
      dentry->d_op->d_release()-->
        dma_buf_release()
          .....
          mutex_lock(&db_list.lock)
          removes the dmabuf from the list
          mutex_unlock(&db_list.lock)

In the above scenario, when dma_buf_put() is called on a dma_buf, it
first frees the dma_buf's file->f_inode(=dentry->d_inode) and then
removes this dma_buf from the system db_list. In between P2 traversing
the db_list tries to access this dma_buf's file->f_inode that was freed
by P1 which is a use-after-free case.

Since, __fput() calls f_op->release first and then later calls the
d_op->d_release, move the dma_buf's db_list removal from d_release() to
f_op->release(). This ensures that dma_buf's file->f_inode is not
accessed after it is released.

Change-Id: I26189301fd225c2796351ea703cf66f472bd35f5
Cc: <stable@vger.kernel.org> # 5.4.x-
Fixes: 4ab59c3c638c ("dma-buf: Move dma_buf_release() from fops to dentry_ops")
Acked-by: default avatarChristian König <christian.koenig@amd.com>
Signed-off-by: default avatarCharan Teja Reddy <charante@codeaurora.org>
Signed-off-by: default avatarSumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: default avatarThomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1609857399-31549-1-git-send-email-charante@codeaurora.org


Signed-off-by: default avatarCharan Teja Reddy <charante@codeaurora.org>
parent e69f8d02

drivers/dma-buf/dma-buf.c

+17 −4
Original line number Diff line number Diff line
@@ -101,10 +101,6 @@ static void dma_buf_release(struct dentry *dentry) 
	 */

	BUG_ON(dmabuf->cb_shared.active || dmabuf->cb_excl.active);



	mutex_lock(&db_list.lock);

	list_del(&dmabuf->list_node);

	mutex_unlock(&db_list.lock);



	dtor_ret = dma_buf_invoke_dtor(dmabuf);



	if (!dtor_ret)
@@ -121,6 +117,22 @@ static void dma_buf_release(struct dentry *dentry) 
	kfree(msm_dma_buf);

}



static int dma_buf_file_release(struct inode *inode, struct file *file)

{

	struct dma_buf *dmabuf;



	if (!is_dma_buf_file(file))

		return -EINVAL;



	dmabuf = file->private_data;



	mutex_lock(&db_list.lock);

	list_del(&dmabuf->list_node);

	mutex_unlock(&db_list.lock);



	return 0;

}



static const struct dentry_operations dma_buf_dentry_ops = {

	.d_dname = dmabuffs_dname,

	.d_release = dma_buf_release,
@@ -446,6 +458,7 @@ static void dma_buf_show_fdinfo(struct seq_file *m, struct file *file) 
}



static const struct file_operations dma_buf_fops = {

	.release	= dma_buf_file_release,

	.mmap		= dma_buf_mmap_internal,

	.llseek		= dma_buf_llseek,

	.poll		= dma_buf_poll,