4.4-stable review patch. If anyone has any objections, please let me know.
------------------
From: Miklos Szeredi <mszeredi@xxxxxxxxxx>
commit b403f0e37a11f84f7ceaf40b0075499e5bcfd220 upstream.
v9fs may be used as lower layer of overlayfs and accessing f_path.dentry
can lead to a crash. In this case it's a NULL pointer dereference in
p9_fid_create().
Fix by replacing direct access of file->f_path.dentry with the
file_dentry() accessor, which will always return a native object.
Reported-by: Alessio Igor Bogani <alessioigorbogani@xxxxxxxxx>
Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Tested-by: Alessio Igor Bogani <alessioigorbogani@xxxxxxxxx>
Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay")
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/9p/vfs_file.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -74,7 +74,7 @@ int v9fs_file_open(struct inode *inode,
v9fs_proto_dotu(v9ses));
fid = file->private_data;
if (!fid) {
- fid = v9fs_fid_clone(file->f_path.dentry);
+ fid = v9fs_fid_clone(file_dentry(file));
if (IS_ERR(fid))
return PTR_ERR(fid);
@@ -100,7 +100,7 @@ int v9fs_file_open(struct inode *inode,
* because we want write after unlink usecase
* to work.
*/
- fid = v9fs_writeback_fid(file->f_path.dentry);
+ fid = v9fs_writeback_fid(file_dentry(file));
if (IS_ERR(fid)) {
err = PTR_ERR(fid);
mutex_unlock(&v9inode->v_mutex);
@@ -516,7 +516,7 @@ v9fs_mmap_file_mmap(struct file *filp, s
* because we want write after unlink usecase
* to work.
*/
- fid = v9fs_writeback_fid(filp->f_path.dentry);
+ fid = v9fs_writeback_fid(file_dentry(filp));
if (IS_ERR(fid)) {
retval = PTR_ERR(fid);
mutex_unlock(&v9inode->v_mutex);
--
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