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SubjectRe: [PATCH v2] isofs compress: Remove VLA usage
On Thu 05-04-18 11:17:20, Kyle Spiers 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@google.com>

This is a good cleanup but the error recovery is hosed. See below...

> ---
> 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;

As Joe pointed out this needs to be:

if (!bhs) {
*errp = -ENOMEM;
return 0;
}

> @@ -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;

And this is wrong as well. You need to do:

if (!pages) {
unlock_page(page);
return -ENOMEM;
}


Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
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