linux-kernel - [RFC PATCH v3 12/59] getname

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Message-ID: <20251216035518.4037331-13-viro@zeniv.linux.org.uk>
Date: Tue, 16 Dec 2025 03:54:31 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: linux-fsdevel@...r.kernel.org
Cc: torvalds@...ux-foundation.org,
	brauner@...nel.org,
	jack@...e.cz,
	mjguzik@...il.com,
	paul@...l-moore.com,
	axboe@...nel.dk,
	audit@...r.kernel.org,
	io-uring@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC PATCH v3 12/59] getname_flags() massage, part 1

In case of long name don't reread what we'd already copied.
memmove() it instead.  That avoids the possibility of ending
up with empty name there and the need to look at the flags
on the slow path.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/namei.c | 33 ++++++++++++++++-----------------
 1 file changed, 16 insertions(+), 17 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index f22cfdff72ab..ea7efbddc7f4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -174,36 +174,35 @@ getname_flags(const char __user *filename, int flags)
 	 */
 	if (unlikely(len == EMBEDDED_NAME_MAX)) {
 		const size_t size = offsetof(struct filename, iname[1]);
-		kname = (char *)result;
+		struct filename *p;
 
 		/*
 		 * size is chosen that way we to guarantee that
 		 * result->iname[0] is within the same object and that
 		 * kname can't be equal to result->iname, no matter what.
 		 */
-		result = kzalloc(size, GFP_KERNEL);
-		if (unlikely(!result)) {
-			__putname(kname);
+		p = kzalloc(size, GFP_KERNEL);
+		if (unlikely(!p)) {
+			__putname(result);
 			return ERR_PTR(-ENOMEM);
 		}
-		result->name = kname;
-		len = strncpy_from_user(kname, filename, PATH_MAX);
+		memmove(result, &result->iname, EMBEDDED_NAME_MAX);
+		kname = (char *)result;
+		p->name = kname;
+		len = strncpy_from_user(kname + EMBEDDED_NAME_MAX,
+					filename + EMBEDDED_NAME_MAX,
+					PATH_MAX - EMBEDDED_NAME_MAX);
 		if (unlikely(len < 0)) {
-			__putname(kname);
-			kfree(result);
+			kfree(p);
+			__putname(result);
 			return ERR_PTR(len);
 		}
-		/* The empty path is special. */
-		if (unlikely(!len) && !(flags & LOOKUP_EMPTY)) {
-			__putname(kname);
-			kfree(result);
-			return ERR_PTR(-ENOENT);
-		}
-		if (unlikely(len == PATH_MAX)) {
-			__putname(kname);
-			kfree(result);
+		if (unlikely(len == PATH_MAX - EMBEDDED_NAME_MAX)) {
+			kfree(p);
+			__putname(result);
 			return ERR_PTR(-ENAMETOOLONG);
 		}
+		result = p;
 	}
 	initname(result);
 	audit_getname(result);
-- 
2.47.3