btrfs: handle empty eb->folios in num_extent_folios()

boryas · mehmetb0 · commit 24a5562a917e · 2025-08-13T15:01:51.000+03:00
BugLink: https://bugs.launchpad.net/bugs/2115678 [ Upstream commit d6fe0c69b3aa5c985380b794bdf8e6e9b1811e60 ] num_extent_folios() unconditionally calls folio_order() on eb->folios[0]. If that is NULL this will be a segfault. It is reasonable for it to return 0 as the number of folios in the eb when the first entry is NULL, so do that instead. Reviewed-by: Qu Wenruo <wqu@suse.com> Signed-off-by: Boris Burkov <boris@bur.io> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Manuel Diewald <manuel.diewald@canonical.com> Signed-off-by: Mehmet Basaran <mehmet.basaran@canonical.com>
diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
@@ -297,6 +297,8 @@ static inline int num_extent_pages(const struct extent_buffer *eb)
  */
 static inline int num_extent_folios(const struct extent_buffer *eb)
 {
+	if (!eb->folios[0])
+		return 0;
 	if (folio_order(eb->folios[0]))
 		return 1;
 	return num_extent_pages(eb);

Original file line number	Diff line number	Diff line change
`@@ -297,6 +297,8 @@ static inline int num_extent_pages(const struct extent_buffer *eb)`
`297`	`297`	`*/`
`298`	`298`	`static inline int num_extent_folios(const struct extent_buffer *eb)`
`299`	`299`	`{`
	`300`	`+ if (!eb->folios[0])`
	`301`	`+ return 0;`
`300`	`302`	`if (folio_order(eb->folios[0]))`
`301`	`303`	`return 1;`
`302`	`304`	`return num_extent_pages(eb);`