Re: [PATCH v2] btrfs: fix the fsverity callback where unexpected range is verified

[Eric Biggers <ebiggers@kernel.org>]

On Sat, Oct 10, 2026 at 04:59:49PM +1030, Qu Wenruo wrote:
> [BUG]
> There is a bug report that on v7.2 kernel, compressed extents with
> fsverity enabled can lead to warnings like the following:
> 
>  fs-verity (dm-3, inode 257): FILE CORRUPTED! pos=7471104, level=-1, want_hash=sha256:bedf0e7bc93b48694db719001a8d3e79229cc58ee638b41d4149193505090774, real_hash=sha256:ad7facb2586fc6e966c004d7d1d16b024f5805ff7cb47c7a85dabd8b48892ca7
> 
> The read itself eventually succeeds, and no read error is returned to
> user space.
> 
> [CAUSE]
> Since v7.2 btrfs has enabled large data folio support, now a folio can
> contain multiple blocks even if the page size matches the fs block size.
> And even before that, btrfs already has block size < page size support,
> thus all involved code should assume a folio can contain multiple
> blocks.
> 
> However the function btrfs_verify_folio() calls fsverity_verify_folio(),
> which verifies the whole folio, even if the read range only covers part
> of the folio.
> 
> This forces fsverity to verify garbage data that is not yet read from
> disk, and causes verification failure.
> 
> This is a long-standing bug, but previously it only affected bs < ps
> cases which is not that common.
> Now with the large folio support, it's much easier to trigger with bs ==
> ps cases.
> 
> [FIX]
> Instead of calling fsverity_verify_folio(), call
> fsverity_verify_blocks() to verify only the read range.
> 
> Reported-by: Roger Alasà <vonbloom@gmail.com>
> Link: https://lore.kernel.org/linux-btrfs/CAELqY9==Ter2XQPRp=gjW5T75T+7kcZCXpn5roF2L6tY6mQNxw@mail.gmail.com/
> Fixes: 146054090b08 ("btrfs: initial fsverity support")
> Tested-by: Roger Alasà <vonbloom@gmail.com>
> Signed-off-by: Qu Wenruo <wqu@suse.com>

Please add 'Cc: stable@vger.kernel.org'

Reviewed-by: Eric Biggers <ebiggers@kernel.org>

- Eric