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SubjectRe: [PATCH v2] zram: fix possible use after free in zcomp_create()
Hello,

First of all, Thanks for catching a bug and review, Guys.
Below there are just some cleanup.
If you guys think it's better, please respin.

On Mon, Sep 07, 2015 at 03:13:10PM +0100, Luis Henriques wrote:
> zcomp_create() verifies the success of zcomp_strm_{multi,siggle}_create()
> through comp->stream, which can potentially be pointing to memory that was
> freed if these functions returned an error.
>
> Fixes: beca3ec71fe5 ("zram: add multi stream functionality")
> Cc: stable@vger.kernel.org
> Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
> ---
> Changes since v1:
> * Check zcomp_strm_{multi,siggle}_create() return code instead
> comp->stream (suggested by Sergey)
>
> drivers/block/zram/zcomp.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/block/zram/zcomp.c b/drivers/block/zram/zcomp.c
> index 965d1afb0eaa..8d2cdfd307db 100644
> --- a/drivers/block/zram/zcomp.c
> +++ b/drivers/block/zram/zcomp.c
> @@ -336,6 +336,7 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
> {
> struct zcomp *comp;
> struct zcomp_backend *backend;
> + int ret;

For the clarification, I want to call it as 'error' instead of ret.

>
> backend = find_backend(compress);
> if (!backend)
> @@ -347,10 +348,10 @@ struct zcomp *zcomp_create(const char *compress, int max_strm)
>
> comp->backend = backend;
> if (max_strm > 1)
> - zcomp_strm_multi_create(comp, max_strm);
> + ret = zcomp_strm_multi_create(comp, max_strm);
> else
> - zcomp_strm_single_create(comp);
> - if (!comp->stream) {
> + ret = zcomp_strm_single_create(comp);
> + if (ret) {
> kfree(comp);
> return ERR_PTR(-ENOMEM);
> }

And we could return ERR_PTR(error) rather than fixed -ENOMEM to propagate
other errors potentially could be happen in future(ex, crypto support).
Of course, we should change description of the function about error return.

Thanks.


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