[PATCH] fs: btrfs: fix out of bounds write

[David Disseldorp]

On Mon, 17 Jun 2024 22:49:47 +0300, Alex Shumsky wrote:

> Fix btrfs_read/read_and_truncate_page write out of bounds of destination
> buffer. Old behavior break bootstd malloc'd buffers of exact file size.
> Previously this OOB write have not been noticed because distroboot usually
> read files into huge static memory areas.
> 
> Signed-off-by: Alex Shumsky <alexthreed at gmail.com>
> ---
> 
>  fs/btrfs/inode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 4691612eda..b51f578b49 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -640,7 +640,7 @@ static int read_and_truncate_page(struct btrfs_path *path,
>  	extent_type = btrfs_file_extent_type(leaf, fi);
>  	if (extent_type == BTRFS_FILE_EXTENT_INLINE) {
>  		ret = btrfs_read_extent_inline(path, fi, buf);
> -		memcpy(dest, buf + page_off, min(page_len, ret));
> +		memcpy(dest, buf + page_off, min(min(page_len, ret), len));

This looks (still) broken for the compressed inline extent error paths,
where ret=-errno .

nit: please prefix your patch subject with "uboot" so that casual
linux-btrfs readers like me don't get confused by matching kernel file
paths.