ksmbd: fix parent dentry lifetime in directory enumeration

ksmbd_populate_dot_dotdot_entries() builds the ".." entry from
the open directory's d_parent and passes that pointer to
ksmbd_vfs_fill_dentry_attrs() without taking a reference. That pointer
is only valid while the directory stays under this parent. If a
concurrent rename moves the directory elsewhere, the old parent loses
its last reference; a following rmdir then turns it into a negative
dentry with d_inode cleared, and after the RCU grace period the dentry
itself is freed. The worker still holds the raw pointer and
dereferences d_inode through vfs_getattr() and vfs_getxattr().

A remote SMB client, authenticated or guest, triggers this by listing
a directory while that directory is moved under a new parent and the
old parent is deleted. It can be done by the client itself with write
access or by other concurrent writers, triggering null-ptr-deref and
slab-use-after-free on a KASAN build.

  KASAN: null-ptr-deref in range
      [0x0000000000000000-0x0000000000000007]
  Workqueue: ksmbd-io handle_ksmbd_work
  RIP: 0010:xattr_permission+0x9d/0x160
  Call Trace:
   vfs_getxattr+0x9c/0x1b0
   ksmbd_vfs_getxattr+0x82/0x100
   ksmbd_vfs_get_dos_attrib_xattr+0x7f/0x130
   ksmbd_vfs_fill_dentry_attrs+0x435/0x650
   ksmbd_populate_dot_dotdot_entries+0x25e/0x630
   smb2_query_dir+0xcf9/0x1a20
   handle_ksmbd_work+0x5f1/0x1c80
   process_one_work+0x90b/0x19d0

Fix by using the dentry reference counting APIs: take the parent with
dget_parent(), take a matching dget() on ".", and dput() the dentry
once ksmbd_vfs_fill_dentry_attrs() has returned or the pattern does
not match.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Cc: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Cen Zhang (Microsoft) <cenzhang@linux.microsoft.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>

0 files changed, 0 insertions, 0 deletions