fix handling of nd->depth on LOOKUP_CACHED failures in try_to_unlazy*

stable inclusion
from stable-v5.10.162
commit 146fe79fff13fea7b5f3a9e913689e07fd4e6432
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/I6BTWC

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=v5.10.167&id=146fe79fff13fea7b5f3a9e913689e07fd4e6432

--------------------------------

[ Upstream commit eacd9aa8 ]

After switching to non-RCU mode, we want nd->depth to match the number
of entries in nd->stack[] that need eventual path_put().
legitimize_links() takes care of that on failures; unfortunately,
failure exits added for LOOKUP_CACHED do not.

We could add the logics for that into those failure exits, both in
try_to_unlazy() and in try_to_unlazy_next(), but since both checks
are immediately followed by legitimize_links() and there's no calls
of legitimize_links() other than those two...  It's easier to
move the check (and required handling of nd->depth on failure) into
legitimize_links() itself.

[caught by Jens: ... and since we are zeroing ->depth here, we need
to do drop_links() first]

Fixes: 6c6ec2b0 "fs: add support for LOOKUP_CACHED"
Tested-by: NJens Axboe <axboe@kernel.dk>
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NLi Lingfeng <lilingfeng3@huawei.com>
Reviewed-by: NZhang Yi <yi.zhang@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: NJialin Zhang <zhangjialin11@huawei.com>

fs/namei.c

@@ -635,6 +635,11 @@ static inline bool legitimize_path(struct nameidata *nd,
 static bool legitimize_links(struct nameidata *nd)
 {
 	int i;
+	if (unlikely(nd->flags & LOOKUP_CACHED)) {
+		drop_links(nd);
+		nd->depth = 0;
+		return false;
+	}
 	for (i = 0; i < nd->depth; i++) {
 		struct saved *last = nd->stack + i;
 		if (unlikely(!legitimize_path(nd, &last->link, last->seq))) {
@@ -691,8 +696,6 @@ static bool try_to_unlazy(struct nameidata *nd)
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	nd->flags &= ~LOOKUP_RCU;
-	if (nd->flags & LOOKUP_CACHED)
-		goto out1;
 	if (unlikely(!legitimize_links(nd)))
 		goto out1;
 	if (unlikely(!legitimize_path(nd, &nd->path, nd->seq)))
@@ -729,8 +732,6 @@ static int unlazy_child(struct nameidata *nd, struct dentry *dentry, unsigned se
 	BUG_ON(!(nd->flags & LOOKUP_RCU));
 
 	nd->flags &= ~LOOKUP_RCU;
-	if (nd->flags & LOOKUP_CACHED)
-		goto out2;
 	if (unlikely(!legitimize_links(nd)))
 		goto out2;
 	if (unlikely(!legitimize_mnt(nd->path.mnt, nd->m_seq)))