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

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Date:   Tue, 28 Jun 2022 08:30:52 +0800
From:   Ian Kent <raven@...maw.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Al Viro <viro@...IV.linux.org.uk>,
        Siddhesh Poyarekar <siddhesh@...plt.org>,
        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

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 <raven@...maw.net>
---
 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 24ce12f0db32..4c735d0ce3cb 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;
 	}