linux-kernel - [PATCH] fs: correctly check for errors from replace_fd() in receive_fd

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Message-Id: <20250801-fix-receive_fd_replace-v1-1-d46d600c74d6@linutronix.de>
Date: Fri, 01 Aug 2025 09:38:38 +0200
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Alexander Viro <viro@...iv.linux.org.uk>, 
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, 
 Sargun Dhillon <sargun@...gun.me>, Kees Cook <kees@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
 stable@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH] fs: correctly check for errors from replace_fd() in
 receive_fd_replace()

replace_fd() returns either a negative error number or the number of the
new file descriptor. The current code misinterprets any positive file
descriptor number as an error.

Only check for negative error numbers, so that __receive_sock() is called
correctly for valid file descriptors.

Fixes: 173817151b15 ("fs: Expand __receive_fd() to accept existing fd")
Fixes: 42eb0d54c08a ("fs: split receive_fd_replace from __receive_fd")
Cc: stable@...r.kernel.org
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
Untested, it stuck out while reading the code.
---
 fs/file.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/file.c b/fs/file.c
index 6d2275c3be9c6967d16c75d1b6521f9b58980926..56c3a045121d8f43a54cf05e6ce1962f896339ac 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -1387,7 +1387,7 @@ int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
 	if (error)
 		return error;
 	error = replace_fd(new_fd, file, o_flags);
-	if (error)
+	if (error < 0)
 		return error;
 	__receive_sock(file);
 	return new_fd;

---
base-commit: 89748acdf226fd1a8775ff6fa2703f8412b286c8
change-id: 20250801-fix-receive_fd_replace-7fdd5ce6532d

Best regards,
-- 
Thomas Weißschuh <thomas.weissschuh@...utronix.de>