[PATCH 6/7] namei: clean up do_linkat retry logic

[Dmitry Kadashev <dkadashev@gmail.com>]

Moving the main logic to a helper function makes the whole thing much
easier to follow.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/io-uring/CAHk-=wiG+sN+2zSoAOggKCGue2kOJvw3rQySvQXsZstRQFTN+g@mail.gmail.com/
Signed-off-by: Dmitry Kadashev <dkadashev@gmail.com>
---
 fs/namei.c | 80 ++++++++++++++++++++++++++++++------------------------
 1 file changed, 44 insertions(+), 36 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index c9110ac83ccb..5e4fa8b65a8d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4380,48 +4380,22 @@ int vfs_link(struct dentry *old_dentry, struct user_namespace *mnt_userns,
 }
 EXPORT_SYMBOL(vfs_link);
 
-/*
- * Hardlinks are often used in delicate situations.  We avoid
- * security-related surprises by not following symlinks on the
- * newname.  --KAB
- *
- * We don't follow them on the oldname either to be compatible
- * with linux 2.0, and to avoid hard-linking to directories
- * and other special files.  --ADM
- */
-int do_linkat(int olddfd, struct filename *old, int newdfd,
-	      struct filename *new, int flags)
+static int linkat_helper(int olddfd, struct filename *old, int newdfd,
+			 struct filename *new, unsigned int lookup_flags)
 {
 	struct user_namespace *mnt_userns;
 	struct dentry *new_dentry;
 	struct path old_path, new_path;
 	struct inode *delegated_inode = NULL;
-	int how = 0;
 	int error;
 
-	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) {
-		error = -EINVAL;
-		goto out_putnames;
-	}
-	/*
-	 * To use null names we require CAP_DAC_READ_SEARCH
-	 * This ensures that not everyone will be able to create
-	 * handlink using the passed filedescriptor.
-	 */
-	if (flags & AT_EMPTY_PATH && !capable(CAP_DAC_READ_SEARCH)) {
-		error = -ENOENT;
-		goto out_putnames;
-	}
-
-	if (flags & AT_SYMLINK_FOLLOW)
-		how |= LOOKUP_FOLLOW;
 retry:
-	error = __filename_lookup(olddfd, old, how, &old_path, NULL);
+	error = __filename_lookup(olddfd, old, lookup_flags, &old_path, NULL);
 	if (error)
-		goto out_putnames;
+		return error;
 
 	new_dentry = __filename_create(newdfd, new, &new_path,
-					(how & LOOKUP_REVAL));
+					(lookup_flags & LOOKUP_REVAL));
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto out_putpath;
@@ -4447,14 +4421,48 @@ int do_linkat(int olddfd, struct filename *old, int newdfd,
 			goto retry;
 		}
 	}
+out_putpath:
+	path_put(&old_path);
+	return error;
+}
+
+/*
+ * Hardlinks are often used in delicate situations.  We avoid
+ * security-related surprises by not following symlinks on the
+ * newname.  --KAB
+ *
+ * We don't follow them on the oldname either to be compatible
+ * with linux 2.0, and to avoid hard-linking to directories
+ * and other special files.  --ADM
+ */
+int do_linkat(int olddfd, struct filename *old, int newdfd,
+	      struct filename *new, int flags)
+{
+	int error, how = 0;
+
+	if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) {
+		error = -EINVAL;
+		goto out;
+	}
+	/*
+	 * To use null names we require CAP_DAC_READ_SEARCH
+	 * This ensures that not everyone will be able to create
+	 * handlink using the passed filedescriptor.
+	 */
+	if (flags & AT_EMPTY_PATH && !capable(CAP_DAC_READ_SEARCH)) {
+		error = -ENOENT;
+		goto out;
+	}
+
+	if (flags & AT_SYMLINK_FOLLOW)
+		how |= LOOKUP_FOLLOW;
+
+	error = linkat_helper(olddfd, old, newdfd, new, how);
 	if (retry_estale(error, how)) {
-		path_put(&old_path);
 		how |= LOOKUP_REVAL;
-		goto retry;
+		error = linkat_helper(olddfd, old, newdfd, new, how);
 	}
-out_putpath:
-	path_put(&old_path);
-out_putnames:
+out:
 	putname(old);
 	putname(new);
 
-- 
2.30.2