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From:   David Howells <dhowells@redhat.com>
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        Alan Jenkins <alan.christopher.jenkins@gmail.com>,
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Subject: Re: [PATCH 31/34] vfs: syscall: Add fspick() to select a superblock for reconfiguration [ver #12]
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Date:   Wed, 17 Oct 2018 14:20:12 +0100
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David Howells <dhowells@redhat.com> wrote:

> I should probably check that the picked point is actually a mountpoint.

The root of the mount object at the path specified, that is, perhaps with
something like the attached.

David
---
diff --git a/fs/fsopen.c b/fs/fsopen.c
index f673e93ac456..aaaaa17a233c 100644
--- a/fs/fsopen.c
+++ b/fs/fsopen.c
@@ -186,6 +186,10 @@ SYSCALL_DEFINE3(fspick, int, dfd, const char __user *, path, unsigned int, flags
 	if (ret < 0)
 		goto err;
 
+	ret = -EINVAL;
+	if (target.mnt->mnt_root != target.dentry)
+		goto err_path;
+
 	fc = vfs_new_fs_context(target.dentry->d_sb->s_type, target.dentry,
 				0, 0, FS_CONTEXT_FOR_RECONFIGURE);
 	if (IS_ERR(fc)) {