namei: make permission helpers idmapped mount aware

The two helpers inode_permission() and generic_permission() are used by
the vfs to perform basic permission checking by verifying that the
caller is privileged over an inode. In order to handle idmapped mounts
we extend the two helpers with an additional user namespace argument.
On idmapped mounts the two helpers will make sure to map the inode
according to the mount's user namespace and then peform identical
permission checks to inode_permission() and generic_permission(). If the
initial user namespace is passed nothing changes so non-idmapped mounts
will see identical behavior as before.

Link: https://lore.kernel.org/r/20210121131959.646623-6-christian.brauner@ubuntu.com
Cc: Christoph Hellwig <hch@lst.de>
Cc: David Howells <dhowells@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

2 files changed, 3 insertions, 3 deletions

diff --git a/fs/proc/base.c b/fs/proc/base.c
index b3422cda2a91..b4ec9293625e 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -751,7 +751,7 @@ static int proc_pid_permission(struct inode *inode, int mask)
 
 		return -EPERM;
 	}
-	return generic_permission(inode, mask);
+	return generic_permission(&init_user_ns, inode, mask);
 }
 
 
@@ -3492,7 +3492,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
 		return 0;
 	}
 
-	return generic_permission(inode, mask);
+	return generic_permission(&init_user_ns, inode, mask);
 }
 
 static const struct inode_operations proc_tid_comm_inode_operations = {
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index cb51763ed554..d6e76461e135 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -281,7 +281,7 @@ int proc_fd_permission(struct inode *inode, int mask)
 	struct task_struct *p;
 	int rv;
 
-	rv = generic_permission(inode, mask);
+	rv = generic_permission(&init_user_ns, inode, mask);
 	if (rv == 0)
 		return rv;