From c17acd24c682322563c9c35bd7ed94f13fed3664 Mon Sep 17 00:00:00 2001 From: Liu Bo Date: Fri, 7 Apr 2017 13:11:10 -0700 Subject: Btrfs: fix segmentation fault when doing dio read [ Upstream commit 97bf5a5589aa3a59c60aa775fc12ec0483fc5002 ] Commit 2dabb3248453 ("Btrfs: Direct I/O read: Work on sectorsized blocks") introduced this bug during iterating bio pages in dio read's endio hook, and it could end up with segment fault of the dio reading task. So the reason is 'if (nr_sectors--)', and it makes the code assume that there is one more block in the same page, so page offset is increased and the bio which is created to repair the bad block then has an incorrect bvec.bv_offset, and a later access of the page content would throw a segmentation fault. This also adds ASSERT to check page offset against page size. Signed-off-by: Liu Bo Reviewed-by: David Sterba Signed-off-by: David Sterba Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 8a05fa7..f089d7d 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -8050,8 +8050,10 @@ next_block_or_try_again: start += sectorsize; - if (nr_sectors--) { + nr_sectors--; + if (nr_sectors) { pgoff += sectorsize; + ASSERT(pgoff < PAGE_SIZE); goto next_block_or_try_again; } } @@ -8157,8 +8159,10 @@ next: ASSERT(nr_sectors); - if (--nr_sectors) { + nr_sectors--; + if (nr_sectors) { pgoff += sectorsize; + ASSERT(pgoff < PAGE_SIZE); goto next_block; } } -- cgit v0.10.2