linux-kernel - [PATCH AUTOSEL 5.2 26/85] btrfs: tree-checker: Check if the file extent end overflows

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Date:   Fri, 26 Jul 2019 09:38:36 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Qu Wenruo <wqu@...e.com>, David Sterba <dsterba@...e.com>,
        Sasha Levin <sashal@...nel.org>, linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.2 26/85] btrfs: tree-checker: Check if the file extent end overflows

From: Qu Wenruo <wqu@...e.com>

[ Upstream commit 4c094c33c9ed4b8d0d814bd1d7ff78e123d15d00 ]

Under certain conditions, we could have strange file extent item in log
tree like:

  item 18 key (69599 108 397312) itemoff 15208 itemsize 53
	extent data disk bytenr 0 nr 0
	extent data offset 0 nr 18446744073709547520 ram 18446744073709547520

The num_bytes + ram_bytes overflow 64 bit type.

For num_bytes part, we can detect such overflow along with file offset
(key->offset), as file_offset + num_bytes should never go beyond u64.

For ram_bytes part, it's about the decompressed size of the extent, not
directly related to the size.
In theory it is OK to have a large value, and put extra limitation
on RAM bytes may cause unexpected false alerts.

So in tree-checker, we only check if the file offset and num bytes
overflow.

Signed-off-by: Qu Wenruo <wqu@...e.com>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/tree-checker.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/fs/btrfs/tree-checker.c b/fs/btrfs/tree-checker.c
index 96fce4bef4e7..ccd5706199d7 100644
--- a/fs/btrfs/tree-checker.c
+++ b/fs/btrfs/tree-checker.c
@@ -132,6 +132,7 @@ static int check_extent_data_item(struct extent_buffer *leaf,
 	struct btrfs_file_extent_item *fi;
 	u32 sectorsize = fs_info->sectorsize;
 	u32 item_size = btrfs_item_size_nr(leaf, slot);
+	u64 extent_end;
 
 	if (!IS_ALIGNED(key->offset, sectorsize)) {
 		file_extent_err(leaf, slot,
@@ -207,6 +208,16 @@ static int check_extent_data_item(struct extent_buffer *leaf,
 	    CHECK_FE_ALIGNED(leaf, slot, fi, num_bytes, sectorsize))
 		return -EUCLEAN;
 
+	/* Catch extent end overflow */
+	if (check_add_overflow(btrfs_file_extent_num_bytes(leaf, fi),
+			       key->offset, &extent_end)) {
+		file_extent_err(leaf, slot,
+	"extent end overflow, have file offset %llu extent num bytes %llu",
+				key->offset,
+				btrfs_file_extent_num_bytes(leaf, fi));
+		return -EUCLEAN;
+	}
+
 	/*
 	 * Check that no two consecutive file extent items, in the same leaf,
 	 * present ranges that overlap each other.
-- 
2.20.1