ACK: [SRU][Artful][PATCH 1/1] iov_iter: fix page_copy_sane for compound pages

[Kleber Souza]

On 06/01/18 09:29, Joseph Salisbury wrote:
> From: Petar Penkov <ppenkov at google.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1772031
> 
> Issue is that if the data crosses a page boundary inside a compound
> page, this check will incorrectly trigger a WARN_ON.
> 
> To fix this, compute the order using the head of the compound page and
> adjust the offset to be relative to that head.
> 
> Fixes: 72e809ed81ed ("iov_iter: sanity checks for copy to/from page
> primitives")
> 
> Signed-off-by: Petar Penkov <ppenkov at google.com>
> CC: Al Viro <viro at zeniv.linux.org.uk>
> CC: Eric Dumazet <edumazet at google.com>
> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
> (cherry picked from commit a90bcb86ae700c12432446c4aa1819e7b8e172ec)
> Signed-off-by: Joseph Salisbury <joseph.salisbury at canonical.com>

Acked-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>

> ---
>  lib/iov_iter.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/lib/iov_iter.c b/lib/iov_iter.c
> index 52c8dd6..1c1c06d 100644
> --- a/lib/iov_iter.c
> +++ b/lib/iov_iter.c
> @@ -687,8 +687,10 @@ EXPORT_SYMBOL(_copy_from_iter_full_nocache);
>  
>  static inline bool page_copy_sane(struct page *page, size_t offset, size_t n)
>  {
> -	size_t v = n + offset;
> -	if (likely(n <= v && v <= (PAGE_SIZE << compound_order(page))))
> +	struct page *head = compound_head(page);
> +	size_t v = n + offset + page_address(page) - page_address(head);
> +
> +	if (likely(n <= v && v <= (PAGE_SIZE << compound_order(head))))
>  		return true;
>  	WARN_ON(1);
>  	return false;
>