The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From 3227788cd369d734d2d3cd94f8af7536b60fa552 Mon Sep 17 00:00:00 2001
From: BingJing Chang <bingjingc@xxxxxxxxxxxx>
Date: Thu, 25 Mar 2021 09:56:22 +0800
Subject: [PATCH] btrfs: fix a potential hole punching failure
In commit d77815461f04 ("btrfs: Avoid trucating page or punching hole
in a already existed hole."), existing holes can be skipped by calling
find_first_non_hole() to adjust start and len. However, if the given len
is invalid and large, when an EXTENT_MAP_HOLE extent is found, len will
not be set to zero because (em->start + em->len) is less than
(start + len). Then the ret will be 1 but len will not be set to 0.
The propagated non-zero ret will result in fallocate failure.
In the while-loop of btrfs_replace_file_extents(), len is not updated
every time before it calls find_first_non_hole(). That is, after
btrfs_drop_extents() successfully drops the last non-hole file extent,
it may fail with ENOSPC when attempting to drop a file extent item
representing a hole. The problem can happen. After it calls
find_first_non_hole(), the cur_offset will be adjusted to be larger
than or equal to end. However, since the len is not set to zero, the
break-loop condition (ret && !len) will not be met. After it leaves the
while-loop, fallocate will return 1, which is an unexpected return
value.
We're not able to construct a reproducible way to let
btrfs_drop_extents() fail with ENOSPC after it drops the last non-hole
file extent but with remaining holes left. However, it's quite easy to
fix. We just need to update and check the len every time before we call
find_first_non_hole(). To make the while loop more readable, we also
pull the variable updates to the bottom of loop like this:
while (cur_offset < end) {
...
// update cur_offset & len
// advance cur_offset & len in hole-punching case if needed
}
Reported-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
Fixes: d77815461f04 ("btrfs: Avoid trucating page or punching hole in a already existed hole.")
CC: stable@xxxxxxxxxxxxxxx # 4.4+
Reviewed-by: Robbie Ko <robbieko@xxxxxxxxxxxx>
Reviewed-by: Chung-Chiang Cheng <cccheng@xxxxxxxxxxxx>
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Signed-off-by: BingJing Chang <bingjingc@xxxxxxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 42634658815f..864c08d08a35 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2730,8 +2730,6 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
extent_info->file_offset += replace_len;
}
- cur_offset = drop_args.drop_end;
-
ret = btrfs_update_inode(trans, root, inode);
if (ret)
break;
@@ -2751,7 +2749,9 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
BUG_ON(ret); /* shouldn't happen */
trans->block_rsv = rsv;
- if (!extent_info) {
+ cur_offset = drop_args.drop_end;
+ len = end - cur_offset;
+ if (!extent_info && len) {
ret = find_first_non_hole(inode, &cur_offset, &len);
if (unlikely(ret < 0))
break;
