[PATCH] namei: revert old behaviour for filename_lookup with LOOKUP_PARENT flag

[Vineeth Remanan Pillai <vineethp@amazon.com>]

filename_lookup used to return success for non-existing file when called
with LOOKUP_PARENT flag. This behaviour was changed with
commit 8bcb77fabd7c ("namei: split off filename_lookupat()
with LOOKUP_PARENT")

The above patch split parent lookup functionality to a different function
filename_parentat and changed all calls to filename_lookup(LOOKUP_PARENT)
to the new function filename_parentat. But functions like kern_path which
passed the flags directly to filename_lookup regressed due to this.

This patch aims to fix the regressed behaviour by calling
filename_parentat from filename_lookup if the flags contain LOOKUP_PARENT.

Signed-off-by: Vineeth Remanan Pillai <vineethp@amazon.com>
---
 fs/namei.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/fs/namei.c b/fs/namei.c
index adb0414..e16ab09 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2292,6 +2292,21 @@ static int filename_lookup(int dfd, struct filename *name, unsigned flags,
 {
 	int retval;
 	struct nameidata nd;
+
+	if (flags & LOOKUP_PARENT) {
+		struct qstr last;
+		struct filename *filename;
+		int type;
+
+		filename = filename_parentat(dfd, name, flags ^ LOOKUP_PARENT,
+					    path, &last, &type);
+		if (IS_ERR(filename))
+			return PTR_ERR(filename);
+
+		putname(filename);
+		return 0;
+	}
+
 	if (IS_ERR(name))
 		return PTR_ERR(name);
 	if (unlikely(root)) {
-- 
2.1.2.AMZN