linux-kernel - [PATCH 1/2] vfs: parse: deal with zero length string value

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Message-ID: <163513470696.40352.1069626993439788071.stgit@mickey.themaw.net>
Date:   Mon, 25 Oct 2021 12:05:06 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH 1/2] vfs: parse: deal with zero length string value

From: Ian Kent <ikent@...hat.com>

Parsing an fs string that has zero length should result in the parameter
being set to NULL so that downstream processing handles it correctly.
For example, the proc mount table processing should print "(none)" in
this case to preserve mount record field count, but if the value points
to the NULL string this doesn't happen.

Signed-off-by: Ian Kent <ikent@...hat.com>
---
 fs/fs_context.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index b7e43a780a62..a949cceccbfd 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -175,9 +175,13 @@ int vfs_parse_fs_string(struct fs_context *fc, const char *key,
 	};
 
 	if (value) {
-		param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
-		if (!param.string)
-			return -ENOMEM;
+		if (!v_size)
+			param.string = NULL;
+		else {
+			param.string = kmemdup_nul(value, v_size, GFP_KERNEL);
+			if (!param.string)
+				return -ENOMEM;
+		}
 		param.type = fs_value_is_string;
 	}