linux-kernel - [PATCH AUTOSEL 6.14 06/15] btrfs: handle empty eb->folios in num_extent

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Message-Id: <20250512180352.437356-6-sashal@kernel.org>
Date: Mon, 12 May 2025 14:03:41 -0400
From: Sasha Levin <sashal@...nel.org>
To: patches@...ts.linux.dev,
	stable@...r.kernel.org
Cc: Boris Burkov <boris@....io>,
	Qu Wenruo <wqu@...e.com>,
	David Sterba <dsterba@...e.com>,
	Sasha Levin <sashal@...nel.org>,
	clm@...com,
	josef@...icpanda.com,
	linux-btrfs@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH AUTOSEL 6.14 06/15] btrfs: handle empty eb->folios in num_extent_folios()

From: Boris Burkov <boris@....io>

[ 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@...e.com>
Signed-off-by: Boris Burkov <boris@....io>
Reviewed-by: David Sterba <dsterba@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/extent_io.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h
index 6c5328bfabc22..2aefc64cdd295 100644
--- 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);
-- 
2.39.5