[PATCH 5.8 111/124] mm: validate inode in mapping_set_error()

[Greg Kroah-Hartman]

From: Minchan Kim <minchan@xxxxxxxxxx>

commit 8b7b2eb131d3476062ffd34358785b44be25172f upstream.

The swap address_space doesn't have host. Thus, it makes kernel crash once
swap write meets error. Fix it.

Fixes: 735e4ae5ba28 ("vfs: track per-sb writeback errors and report them to syncfs")
Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Andres Freund <andres@xxxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lkml.kernel.org/r/20201010000650.750063-1-minchan@xxxxxxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 include/linux/pagemap.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -54,7 +54,8 @@ static inline void mapping_set_error(str
 	__filemap_set_wb_err(mapping, error);
 
 	/* Record it in superblock */
-	errseq_set(&mapping->host->i_sb->s_wb_err, error);
+	if (mapping->host)
+		errseq_set(&mapping->host->i_sb->s_wb_err, error);
 
 	/* Record it in flags for now, for legacy callers */
 	if (error == -ENOSPC)