ksmbd: prevent out of share access

Because of .., files outside the share directory
could be accessed. To prevent this, normalize
the given path and remove all . and ..
components.

In addition to the usual large set of regression tests (smbtorture
and xfstests), ran various tests on this to specifically check
path name validation including libsmb2 tests to verify path
normalization:

 ./examples/smb2-ls-async smb://172.30.1.15/homes2/../
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/../
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/../../
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/../
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/..bar/
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/bar../
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/bar..
 ./examples/smb2-ls-async smb://172.30.1.15/homes2/foo/bar../../../../

Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>

1 files changed, 9 insertions, 5 deletions

diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index c86164dc70bb..46e0275a77a8 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -634,7 +634,7 @@ static char *
 smb2_get_name(struct ksmbd_share_config *share, const char *src,
 	      const int maxlen, struct nls_table *local_nls)
 {
-	char *name, *unixname;
+	char *name, *norm_name, *unixname;
 
 	name = smb_strndup_from_utf16(src, maxlen, 1, local_nls);
 	if (IS_ERR(name)) {
@@ -643,11 +643,15 @@ smb2_get_name(struct ksmbd_share_config *share, const char *src,
 	}
 
 	/* change it to absolute unix name */
-	ksmbd_conv_path_to_unix(name);
-	ksmbd_strip_last_slash(name);
-
-	unixname = convert_to_unix_name(share, name);
+	norm_name = ksmbd_conv_path_to_unix(name);
+	if (IS_ERR(norm_name)) {
+		kfree(name);
+		return norm_name;
+	}
 	kfree(name);
+
+	unixname = convert_to_unix_name(share, norm_name);
+	kfree(norm_name);
 	if (!unixname) {
 		pr_err("can not convert absolute name\n");
 		return ERR_PTR(-ENOMEM);