From 7aa6bc3e8766990824f66ca76c19596ce10daf3e Mon Sep 17 00:00:00 2001 From: Joanne Koong Date: Mon, 22 Sep 2025 11:00:42 -0700 Subject: [PATCH] iomap: adjust read range correctly for non-block-aligned positions iomap_adjust_read_range() assumes that the position and length passed in are block-aligned. This is not always the case however, as shown in the syzbot generated case for erofs. This causes too many bytes to be skipped for uptodate blocks, which results in returning the incorrect position and length to read in. If all the blocks are uptodate, this underflows length and returns a position beyond the folio. Fix the calculation to also take into account the block offset when calculating how many bytes can be skipped for uptodate blocks. Signed-off-by: Joanne Koong Tested-by: syzbot@syzkaller.appspotmail.com Reviewed-by: Brian Foster Reviewed-by: Christoph Hellwig Signed-off-by: Christian Brauner --- fs/iomap/buffered-io.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 6cc2ee44bbca3..9535733ed07a2 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -240,17 +240,24 @@ static void iomap_adjust_read_range(struct inode *inode, struct folio *folio, * to avoid reading in already uptodate ranges. */ if (ifs) { - unsigned int i; + unsigned int i, blocks_skipped; /* move forward for each leading block marked uptodate */ - for (i = first; i <= last; i++) { + for (i = first; i <= last; i++) if (!ifs_block_is_uptodate(ifs, i)) break; - *pos += block_size; - poff += block_size; - plen -= block_size; - first++; + + blocks_skipped = i - first; + if (blocks_skipped) { + unsigned long block_offset = *pos & (block_size - 1); + unsigned bytes_skipped = + (blocks_skipped << block_bits) - block_offset; + + *pos += bytes_skipped; + poff += bytes_skipped; + plen -= bytes_skipped; } + first = i; /* truncate len if we find any trailing uptodate block(s) */ while (++i <= last) { -- 2.47.3