[PATCH 1/2] btrfs: fix off-by-one end related to inode_need_compress()
From: Qu Wenruo <hidden>
Date: 2026-09-10 02:06:24
Subsystem:
btrfs file system, filesystems (vfs and infrastructure), the rest · Maintainers:
David Sterba, Alexander Viro, Christian Brauner, Linus Torvalds
In most cases btrfs uses @end as the inclusive end bytenr for a range, and this applies to inode_need_compress(). However we have several sites not following the inclusive bytenr: - run_delalloc_inline() Which assigned @blocksize as @end for inode_need_compress() This makes inode_need_compress() always skip the disk_i_size check. - heuristic_collect_sample() Which assigned "start + BTRFS_MAX_UNCOMPRESSED" to @end, which is the exclusive bytenr. Neither is really causing any real problem, as heuristic_collect_sample() has proper checks to avoid reading anything beyond @end, and the sampling read size is 16 bytes, so it has enough headroom to handle that off-by-one problem. But still I do not like anything out of the common scheme, so fix the off-by-one @end for both call sites, and add extra ASSERT()s to catch such unaligned parameters. Signed-off-by: Qu Wenruo <redacted> --- fs/btrfs/compression.c | 15 +++++++-------- fs/btrfs/inode.c | 5 ++++- 2 files changed, 11 insertions(+), 9 deletions(-)
diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index 20169d028961..0134b9253702 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c@@ -1488,11 +1488,14 @@ static bool sample_repeated_patterns(struct heuristic_ws *ws) static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, struct heuristic_ws *ws) { + const u32 blocksize = BTRFS_I(inode)->root->fs_info->sectorsize; struct folio *folio; pgoff_t index, index_end; u32 i, curr_sample_pos; u8 *in_data; + ASSERT(IS_ALIGNED(start, blocksize) && IS_ALIGNED(end + 1, blocksize)); + /* * Compression handles the input data by chunks of 128KiB * (defined by BTRFS_MAX_UNCOMPRESSED)
@@ -1502,18 +1505,14 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, * MAX_SAMPLE_SIZE - calculated under assumption that heuristic will * process no more than BTRFS_MAX_UNCOMPRESSED at a time. */ - if (end - start > BTRFS_MAX_UNCOMPRESSED) - end = start + BTRFS_MAX_UNCOMPRESSED; + if (end + 1 - start > BTRFS_MAX_UNCOMPRESSED) + end = start + BTRFS_MAX_UNCOMPRESSED - 1; index = start >> PAGE_SHIFT; index_end = end >> PAGE_SHIFT; - /* Don't miss unaligned end */ - if (!PAGE_ALIGNED(end)) - index_end++; - curr_sample_pos = 0; - while (index < index_end) { + while (index <= index_end) { folio = filemap_get_folio(inode->i_mapping, index); ASSERT(!IS_ERR(folio)); in_data = kmap_local_folio(folio,
@@ -1522,7 +1521,7 @@ static void heuristic_collect_sample(struct inode *inode, u64 start, u64 end, i = start % PAGE_SIZE; while (i < PAGE_SIZE - SAMPLING_READ_SIZE) { /* Don't sample any garbage from the last page */ - if (start > end - SAMPLING_READ_SIZE) + if (start > end + 1 - SAMPLING_READ_SIZE) break; memcpy(&ws->sample[curr_sample_pos], &in_data[i], SAMPLING_READ_SIZE);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index a85a7c561cf8..79f2181dc631 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c@@ -730,6 +730,9 @@ static inline int inode_need_compress(struct btrfs_inode *inode, u64 start, u64 end, bool check_inline) { struct btrfs_fs_info *fs_info = inode->root->fs_info; + const u32 blocksize = fs_info->sectorsize; + + ASSERT(IS_ALIGNED(start, blocksize) && IS_ALIGNED(end + 1, blocksize)); if (unlikely(!btrfs_inode_can_compress(inode))) { DEBUG_WARN("BTRFS: unexpected compression for ino %llu", btrfs_ino(inode));
@@ -2331,7 +2334,7 @@ static int run_delalloc_inline(struct btrfs_inode *inode, struct folio *locked_f btrfs_check_folio_write_protected(locked_folio); if (btrfs_inode_can_compress(inode) && - inode_need_compress(inode, 0, blocksize, true)) { + inode_need_compress(inode, 0, blocksize - 1, true)) { if (inode->defrag_compress > 0 && inode->defrag_compress < BTRFS_NR_COMPRESS_TYPES) { compress_type = inode->defrag_compress;
--
2.55.0