[PATCH] net/rds: Fix a use after free in rds_message_map_pages

[PATCH] net/rds: Fix a use after free in rds_message_map_pages

[Lv Yunlong]

In rds_message_map_pages, the rm is freed by rds_message_put(rm).
But rm is still used by rm->data.op_sg in return value.

My patch replaces ERR_CAST(rm->data.op_sg) to ERR_PTR(-ENOMEM) to avoid
the uaf.

Fixes: 7dba92037baf3 ("net/rds: Use ERR_PTR for rds_message_alloc_sgs()")
Signed-off-by: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
---
 net/rds/message.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/rds/message.c b/net/rds/message.c
index 071a261fdaab..cecd968c9b25 100644
--- a/net/rds/message.c
+++ b/net/rds/message.c
@@ -348,7 +348,7 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
 	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
 	if (IS_ERR(rm->data.op_sg)) {
 		rds_message_put(rm);
-		return ERR_CAST(rm->data.op_sg);
+		return ERR_PTR(-ENOMEM);
 	}
 
 	for (i = 0; i < rm->data.op_nents; ++i) {
-- 
2.25.1

Re: [PATCH] net/rds: Fix a use after free in rds_message_map_pages

[David Miller]

From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
Date: Tue, 30 Mar 2021 03:16:02 -0700

> @@ -348,7 +348,7 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
>  	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
>  	if (IS_ERR(rm->data.op_sg)) {
>  		rds_message_put(rm);
> -		return ERR_CAST(rm->data.op_sg);
> +		return ERR_PTR(-ENOMEM);
>  	}
>  
>  	for (i = 0; i < rm->data.op_nents; ++i) {

Maybe instead do:

      int err = ERR_CAST(rm->data.op_sg);
      rds_message_put(rm);
      return err;

Then if rds_message_alloc_sgs() starts to return other errors, they will propagate.

Thank you.

Re: Re: [PATCH] net/rds: Fix a use after free in rds_message_map_pages

[lyl2019]

> -----原始邮件-----
> 发件人: "David Miller" <davem@davemloft.net>
> 发送时间: 2021-03-31 08:02:28 (星期三)
> 收件人: lyl2019@mail.ustc.edu.cn
> 抄送: santosh.shilimkar@oracle.com, kuba@kernel.org, netdev@vger.kernel.org, linux-rdma@vger.kernel.org, rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org
> 主题: Re: [PATCH] net/rds: Fix a use after free in rds_message_map_pages
> 
> From: Lv Yunlong <lyl2019@mail.ustc.edu.cn>
> Date: Tue, 30 Mar 2021 03:16:02 -0700
> 
> > @@ -348,7 +348,7 @@ struct rds_message *rds_message_map_pages(unsigned long *page_addrs, unsigned in
> >  	rm->data.op_sg = rds_message_alloc_sgs(rm, num_sgs);
> >  	if (IS_ERR(rm->data.op_sg)) {
> >  		rds_message_put(rm);
> > -		return ERR_CAST(rm->data.op_sg);
> > +		return ERR_PTR(-ENOMEM);
> >  	}
> >  
> >  	for (i = 0; i < rm->data.op_nents; ++i) {
> 
> Maybe instead do:
> 
>       int err = ERR_CAST(rm->data.op_sg);
>       rds_message_put(rm);
>       return err;
> 
> Then if rds_message_alloc_sgs() starts to return other errors, they will propagate.
> 
> Thank you.

The type of ERR_CAST() is void *, not int. 
I think the correct patch is:

        void *err = ERR_CAST(rm->data.op_sg);
        rds_message_put(rm);
        return err;

I have submitted the PATCH v2 for you to review.

Thanks.