Patch "Btrfs: fix segmentation fault when doing dio read" has been added to the 4.9-stable tree

Patch "Btrfs: fix segmentation fault when doing dio read" has been added to the 4.9-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    Btrfs: fix segmentation fault when doing dio read

to the 4.9-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     btrfs-fix-segmentation-fault-when-doing-dio-read.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Oct  5 10:28:31 CEST 2017
From: Liu Bo <bo.li.liu@oracle.com>
Date: Fri, 7 Apr 2017 13:11:10 -0700
Subject: Btrfs: fix segmentation fault when doing dio read

From: Liu Bo <bo.li.liu@oracle.com>


[ 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 <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/btrfs/inode.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- 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;
 		}
 	}


Patches currently in stable-queue which might be from bo.li.liu@oracle.com are

queue-4.9/btrfs-fix-potential-use-after-free-for-cloned-bio.patch
queue-4.9/btrfs-fix-segmentation-fault-when-doing-dio-read.patch