Am 04.01.21 um 12:36 schrieb Charan Teja Reddy:
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.
Fixes: 4ab59c3c638c ("dma-buf: Move dma_buf_release() from fops to dentry_ops")
Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
Not an expert on the debugfs stuff in DMA-buf, but the explanation
sounds perfectly correct to me.
Acked-by: Christian König <christian.koenig@xxxxxxx>
---
drivers/dma-buf/dma-buf.c | 21 +++++++++++++++++----
1 file changed, 17 insertions(+), 4 deletions(-)
diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
index 0eb80c1..a14dcbb 100644
--- a/drivers/dma-buf/dma-buf.c
+++ b/drivers/dma-buf/dma-buf.c
@@ -76,10 +76,6 @@ static void dma_buf_release(struct dentry *dentry)
dmabuf->ops->release(dmabuf);
- mutex_lock(&db_list.lock);
- list_del(&dmabuf->list_node);
- mutex_unlock(&db_list.lock);
-
if (dmabuf->resv == (struct dma_resv *)&dmabuf[1])
dma_resv_fini(dmabuf->resv);
@@ -88,6 +84,22 @@ static void dma_buf_release(struct dentry *dentry)
kfree(dmabuf);
}
+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,
@@ -413,6 +425,7 @@ 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,
