linux-kernel - Re: [PATCH v2] isofs compress: Remove VLA usage

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Message-ID: <CAGXu5j++oA7Vdkt51TnS3GzvNTqkbPk_9upG3oyRtLj_0suCXQ@mail.gmail.com>
Date:   Thu, 5 Apr 2018 11:18:50 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Kyle Spiers <ksspiers@...gle.com>
Cc:     Jan Kara <jack@...e.cz>, Arnd Bergmann <arnd@...db.de>,
        David Howells <dhowells@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Greg KH <gregkh@...uxfoundation.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] isofs compress: Remove VLA usage

On Thu, Apr 5, 2018 at 11:17 AM, Kyle Spiers <ksspiers@...gle.com> wrote:
> As part of the effort to remove VLAs from the kernel[1], this changes
> the allocation of the bhs and pages arrays from being on the stack to being
> kcalloc()ed. This also allows for the removal of the explicit zeroing
> of bhs.
>
> https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kyle Spiers <ksspiers@...gle.com>

Looks good! Thanks for fixing the sparc64 build failure. :)

Reviewed-by: Kees Cook <keescook@...omium.org>

-Kees

> ---
>  fs/isofs/compress.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/fs/isofs/compress.c b/fs/isofs/compress.c
> index 9bb2fe35799d..4eba16bf173c 100644
> --- a/fs/isofs/compress.c
> +++ b/fs/isofs/compress.c
> @@ -20,6 +20,7 @@
>  #include <linux/init.h>
>  #include <linux/bio.h>
>
> +#include <linux/slab.h>
>  #include <linux/vmalloc.h>
>  #include <linux/zlib.h>
>
> @@ -59,7 +60,7 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start,
>                                 >> bufshift;
>         int haveblocks;
>         blkcnt_t blocknum;
> -       struct buffer_head *bhs[needblocks + 1];
> +       struct buffer_head **bhs;
>         int curbh, curpage;
>
>         if (block_size > deflateBound(1UL << zisofs_block_shift)) {
> @@ -80,7 +81,9 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start,
>
>         /* Because zlib is not thread-safe, do all the I/O at the top. */
>         blocknum = block_start >> bufshift;
> -       memset(bhs, 0, (needblocks + 1) * sizeof(struct buffer_head *));
> +       bhs = kcalloc(needblocks + 1, sizeof(*bhs), GFP_KERNEL);
> +       if (!bhs)
> +               return -ENOMEM;
>         haveblocks = isofs_get_blocks(inode, blocknum, bhs, needblocks);
>         ll_rw_block(REQ_OP_READ, 0, haveblocks, bhs);
>
> @@ -190,6 +193,7 @@ static loff_t zisofs_uncompress_block(struct inode *inode, loff_t block_start,
>  b_eio:
>         for (i = 0; i < haveblocks; i++)
>                 brelse(bhs[i]);
> +       kfree(bhs);
>         return stream.total_out;
>  }
>
> @@ -305,7 +309,7 @@ static int zisofs_readpage(struct file *file, struct page *page)
>         unsigned int zisofs_pages_per_cblock =
>                 PAGE_SHIFT <= zisofs_block_shift ?
>                 (1 << (zisofs_block_shift - PAGE_SHIFT)) : 0;
> -       struct page *pages[max_t(unsigned, zisofs_pages_per_cblock, 1)];
> +       struct page **pages;
>         pgoff_t index = page->index, end_index;
>
>         end_index = (inode->i_size + PAGE_SIZE - 1) >> PAGE_SHIFT;
> @@ -330,6 +334,10 @@ static int zisofs_readpage(struct file *file, struct page *page)
>                 full_page = 0;
>                 pcount = 1;
>         }
> +       pages = kcalloc(max_t(unsigned int, zisofs_pages_per_cblock, 1),
> +                                       sizeof(*pages), GFP_KERNEL);
> +       if (!pages)
> +               return -ENOMEM;
>         pages[full_page] = page;
>
>         for (i = 0; i < pcount; i++, index++) {
> @@ -357,6 +365,7 @@ static int zisofs_readpage(struct file *file, struct page *page)
>         }
>
>         /* At this point, err contains 0 or -EIO depending on the "critical" page */
> +       kfree(pages);
>         return err;
>  }
>
> --
> 2.17.0.484.g0c8726318c-goog
>



-- 
Kees Cook
Pixel Security