linux-kernel - Re: [PATCH 2/3] change libfs sb creation routines to avoid collisions with their root inodes

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Message-Id: <200701112008.l0BK8vwA011835@dantu.rdu.redhat.com>
Date:	Thu, 11 Jan 2007 15:08:57 -0500
From:	Jeff Layton <jlayton@...hat.com>
To:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] change libfs sb creation routines to avoid collisions with their root inodes

Yet another respin. It's awfully easy to pass in a files array that will
conflict with the root inode. Add in a check and warning for that. It would
be nice if it were possible to make it so this couldn't happen by design,
I don't see how to do that, given that some filesystems need control over
what inode numbers these entries receive.

This one is untested, but the only change from the last one is the
if/printk.

Signed-off-by: Jeff Layton <jlayton@...hat.com>

diff --git a/drivers/infiniband/hw/ipath/ipath_fs.c b/drivers/infiniband/hw/ipath/ipath_fs.c
index 79a60f0..6ce7926 100644
--- a/drivers/infiniband/hw/ipath/ipath_fs.c
+++ b/drivers/infiniband/hw/ipath/ipath_fs.c
@@ -510,7 +510,7 @@ static int ipathfs_fill_super(struct super_block *sb, void *data,
 	int ret;
 
 	static struct tree_descr files[] = {
-		[1] = {"atomic_stats", &atomic_stats_ops, S_IRUGO},
+		[2] = {"atomic_stats", &atomic_stats_ops, S_IRUGO},
 		{""},
 	};
 
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index c2e0825..023d825 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -727,8 +727,8 @@ static struct super_operations s_ops = {
 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 {
 	static struct tree_descr bm_files[] = {
-		[1] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
-		[2] = {"register", &bm_register_operations, S_IWUSR},
+		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
+		[3] = {"register", &bm_register_operations, S_IWUSR},
 		/* last one */ {""}
 	};
 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
diff --git a/fs/inode.c b/fs/inode.c
diff --git a/fs/libfs.c b/fs/libfs.c
index 503898d..c8f5532 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -217,6 +217,12 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name,
 	root = new_inode(s);
 	if (!root)
 		goto Enomem;
+	/*
+	 * since this is the first inode, make it number 1. New inodes created
+	 * after this must take care not to collide with it (by passing
+	 * max_reserved of 1 to iunique).
+	 */
+	root->i_ino = 1;
 	root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
 	root->i_uid = root->i_gid = 0;
 	root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
@@ -356,6 +362,11 @@ int simple_commit_write(struct file *file, struct page *page,
 	return 0;
 }
 
+/*
+ * the inodes created here are not hashed. If you use iunique to generate
+ * unique inode values later for this filesystem, then you must take care
+ * to pass it an appropriate max_reserved value to avoid collisions.
+ */
 int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
 {
 	static struct super_operations s_ops = {.statfs = simple_statfs};
@@ -373,6 +384,11 @@ int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files
 	inode = new_inode(s);
 	if (!inode)
 		return -ENOMEM;
+	/*
+	 * because the root inode is 1, the files array must not contain an
+	 * entry at index 1
+	 */
+	inode->i_ino = 1;
 	inode->i_mode = S_IFDIR | 0755;
 	inode->i_uid = inode->i_gid = 0;
 	inode->i_blocks = 0;
@@ -388,6 +404,13 @@ int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files
 	for (i = 0; !files->name || files->name[0]; i++, files++) {
 		if (!files->name)
 			continue;
+
+		/* warn if it tries to conflict with the root inode */
+		if (unlikely(i = 1))
+			printk(KERN_WARNING "%s: %s passed in a files array"
+				"with an index of 1!\n", __func__,
+				s->s_type->name);
+
 		dentry = d_alloc_name(root, files->name);
 		if (!dentry)
 			goto out;
-
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