xfs: validate allocated inode number

When we have corrupted free inode btrees, we can attempt to
allocate inodes that we know are already allocated. Catch allocation
of these inodes and report corruption as early as possible to
prevent corruption propagation or deadlocks.
Signed-Off-By: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NCarlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_inode.c

@@ -790,6 +790,18 @@ xfs_ialloc(
 	}
 	ASSERT(*ialloc_context == NULL);
 
+	/*
+	 * Protect against obviously corrupt allocation btree records. Later
+	 * xfs_iget checks will catch re-allocation of other active in-memory
+	 * and on-disk inodes. If we don't catch reallocating the parent inode
+	 * here we will deadlock in xfs_iget() so we have to do these checks
+	 * first.
+	 */
+	if ((pip && ino == pip->i_ino) || !xfs_verify_dir_ino(mp, ino)) {
+		xfs_alert(mp, "Allocated a known in-use inode 0x%llx!", ino);
+		return -EFSCORRUPTED;
+	}
+
 	/*
 	 * Get the in-core inode with the lock held exclusively.
 	 * This is because we're setting fields here we need