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btrfs: fix a potential hole punching failure
In commitd77815461f
("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@synology.com> Fixes:d77815461f
("btrfs: Avoid trucating page or punching hole in a already existed hole.") CC: stable@vger.kernel.org # 4.4+ Reviewed-by: Robbie Ko <robbieko@synology.com> Reviewed-by: Chung-Chiang Cheng <cccheng@synology.com> Reviewed-by: Filipe Manana <fdmanana@suse.com> Signed-off-by: BingJing Chang <bingjingc@synology.com> Signed-off-by: David Sterba <dsterba@suse.com>
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@ -2730,8 +2730,6 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
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extent_info->file_offset += replace_len;
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}
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cur_offset = drop_args.drop_end;
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ret = btrfs_update_inode(trans, root, inode);
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if (ret)
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break;
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@ -2751,7 +2749,9 @@ int btrfs_replace_file_extents(struct btrfs_inode *inode,
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BUG_ON(ret); /* shouldn't happen */
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trans->block_rsv = rsv;
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if (!extent_info) {
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cur_offset = drop_args.drop_end;
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len = end - cur_offset;
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if (!extent_info && len) {
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ret = find_first_non_hole(inode, &cur_offset, &len);
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if (unlikely(ret < 0))
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break;
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