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) --- fs/smb/server/smb_common.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/smb/server/smb_common.c b/fs/smb/server/smb_common.c index ec6ee56293ce..8e44b15a4177 100644 --- a/fs/smb/server/smb_common.c +++ b/fs/smb/server/smb_common.c @@ -478,16 +478,17 @@ int ksmbd_populate_dot_dotdot_entries(struct ksmbd_work *work, int info_level, if (i == 0) { d_info->name = "."; d_info->name_len = 1; - dentry = dir->filp->f_path.dentry; + dentry = dget(dir->filp->f_path.dentry); } else { d_info->name = ".."; d_info->name_len = 2; - dentry = dir->filp->f_path.dentry->d_parent; + dentry = dget_parent(dir->filp->f_path.dentry); } if (!match_pattern(d_info->name, d_info->name_len, search_pattern)) { dir->dot_dotdot[i] = 1; + dput(dentry); continue; } @@ -496,6 +497,7 @@ int ksmbd_populate_dot_dotdot_entries(struct ksmbd_work *work, int info_level, idmap, dentry, &ksmbd_kstat); + dput(dentry); if (rc) break; -- 2.55.0