linux-kernel - [PATCH 3.16 184/192] Compare prepaths when comparing superblocks

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Message-ID: <lsq.1507553065.239245205@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:25 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Aurelien Aptel" <aaptel@...e.com>,
        "Sachin Prabhu" <sprabhu@...hat.com>,
        "Steve French" <smfrench@...il.com>
Subject: [PATCH 3.16 184/192] Compare prepaths when comparing superblocks

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Sachin Prabhu <sprabhu@...hat.com>

commit c1d8b24d18192764fe82067ec6aa8d4c3bf094e0 upstream.

The patch
fs/cifs: make share unaccessible at root level mountable
makes use of prepaths when any component of the underlying path is
inaccessible.

When mounting 2 separate shares having different prepaths but are other
wise similar in other respects, we end up sharing superblocks when we
shouldn't be doing so.

Signed-off-by: Sachin Prabhu <sprabhu@...hat.com>
Tested-by: Aurelien Aptel <aaptel@...e.com>
Signed-off-by: Steve French <smfrench@...il.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/cifs/connect.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

--- a/fs/cifs/connect.c
+++ b/fs/cifs/connect.c
@@ -2751,6 +2751,24 @@ compare_mount_options(struct super_block
 	return 1;
 }
 
+static int
+match_prepath(struct super_block *sb, struct cifs_mnt_data *mnt_data)
+{
+	struct cifs_sb_info *old = CIFS_SB(sb);
+	struct cifs_sb_info *new = mnt_data->cifs_sb;
+
+	if (old->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH) {
+		if (!(new->mnt_cifs_flags & CIFS_MOUNT_USE_PREFIX_PATH))
+			return 0;
+		/* The prepath should be null terminated strings */
+		if (strcmp(new->prepath, old->prepath))
+			return 0;
+
+		return 1;
+	}
+	return 0;
+}
+
 int
 cifs_match_super(struct super_block *sb, void *data)
 {
@@ -2778,7 +2796,8 @@ cifs_match_super(struct super_block *sb,
 
 	if (!match_server(tcp_srv, volume_info) ||
 	    !match_session(ses, volume_info) ||
-	    !match_tcon(tcon, volume_info->UNC)) {
+	    !match_tcon(tcon, volume_info->UNC) ||
+	    !match_prepath(sb, mnt_data)) {
 		rc = 0;
 		goto out;
 	}