Re: [PATCH v2] Btrfs: fix null pointer dereference on compressed write path error

[Liu Bo <obuil.liubo@gmail.com>]

On Fri, Oct 12, 2018 at 4:38 PM <fdmanana@kernel.org> wrote:
>
> From: Filipe Manana <fdmanana@suse.com>
>
> At inode.c:compress_file_range(), under the "free_pages_out" label, we can
> end up dereferencing the "pages" pointer when it has a NULL value. This
> case happens when "start" has a value of 0 and we fail to allocate memory
> for the "pages" pointer. When that happens we jump to the "cont" label and
> then enter the "if (start == 0)" branch where we immediately call the
> cow_file_range_inline() function. If that function returns 0 (success
> creating an inline extent) or an error (like -ENOMEM for example) we jump
> to the "free_pages_out" label and then access "pages[i]" leading to a NULL
> pointer dereference, since "nr_pages" has a value greater than zero at
> that point.
>
> Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
> the "pages" pointer.
>

Looks good.

Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>

thanks,
liubo

> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
> Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>
> V2: Updated changelog.
>
>  fs/btrfs/inode.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 66c6c4103d2f..d6b61b1facdd 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -503,6 +503,7 @@ static noinline void compress_file_range(struct inode *inode,
>                 pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
>                 if (!pages) {
>                         /* just bail out to the uncompressed code */
> +                       nr_pages = 0;
>                         goto cont;
>                 }
>
> --
> 2.11.0
>