[PATCH] fs/btrfs: Zero file data not backed by extents

[PATCH] fs/btrfs: Zero file data not backed by extents

[Fabian Vogt]

Implicit holes in file data need to be zeroed explicitly, instead of
just leaving the data in the buffer uninitialized.

This led to kernels randomly failing to boot in "fun" ways when loaded
from btrfs with the no_holes feature enabled, because large blocks of
zeros in the kernel file contained random data instead.

Signed-off-by: Fabian Vogt <fvogt@suse.de>
---
 grub-core/fs/btrfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
index 19bff4610..ba0c58352 100644
--- a/grub-core/fs/btrfs.c
+++ b/grub-core/fs/btrfs.c
@@ -1603,6 +1603,8 @@ grub_btrfs_extent_read (struct grub_btrfs_data *data,
 	      csize = grub_le_to_cpu64 (key_out.offset) - pos;
 	      if (csize > len)
 		      csize = len;
+
+	      grub_memset (buf, 0, csize);
 	      buf += csize;
 	      pos += csize;
 	      len -= csize;
-- 
2.42.0





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Re: [PATCH] fs/btrfs: Zero file data not backed by extents

[Daniel Kiper]

On Thu, Oct 05, 2023 at 03:57:44PM +0200, Fabian Vogt wrote:
> Implicit holes in file data need to be zeroed explicitly, instead of
> just leaving the data in the buffer uninitialized.
>
> This led to kernels randomly failing to boot in "fun" ways when loaded
> from btrfs with the no_holes feature enabled, because large blocks of
> zeros in the kernel file contained random data instead.
>
> Signed-off-by: Fabian Vogt <fvogt@suse.de>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel

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Re: [PATCH] fs/btrfs: Zero file data not backed by extents

[Qu Wenruo]

On 2023/10/6 00:27, Fabian Vogt wrote:
> Implicit holes in file data need to be zeroed explicitly, instead of
> just leaving the data in the buffer uninitialized.
> 
> This led to kernels randomly failing to boot in "fun" ways when loaded
> from btrfs with the no_holes feature enabled, because large blocks of
> zeros in the kernel file contained random data instead.
> 
> Signed-off-by: Fabian Vogt <fvogt@suse.de>

Reviewed-by: Qu Wenruo <wqu@suse.com>

Thanks,
Qu
> ---
>   grub-core/fs/btrfs.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/grub-core/fs/btrfs.c b/grub-core/fs/btrfs.c
> index 19bff4610..ba0c58352 100644
> --- a/grub-core/fs/btrfs.c
> +++ b/grub-core/fs/btrfs.c
> @@ -1603,6 +1603,8 @@ grub_btrfs_extent_read (struct grub_btrfs_data *data,
>   	      csize = grub_le_to_cpu64 (key_out.offset) - pos;
>   	      if (csize > len)
>   		      csize = len;
> +
> +	      grub_memset (buf, 0, csize);
>   	      buf += csize;
>   	      pos += csize;
>   	      len -= csize;

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