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Subject: Re: [Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak
 in rds_notify_queue_get()
To:     Peilin Ye <yepeilin.cs@gmail.com>
Cc:     "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Dan Carpenter <dan.carpenter@oracle.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-kernel-mentees@lists.linuxfoundation.org,
        netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
        rds-devel@oss.oracle.com, linux-kernel@vger.kernel.org
References: <20200730192026.110246-1-yepeilin.cs@gmail.com>
From:   "santosh.shilimkar@oracle.com" <santosh.shilimkar@oracle.com>
Organization: Oracle Corporation
Message-ID: <2b21c0e4-2783-74f6-313b-9f6cb17c545a@oracle.com>
Date:   Thu, 30 Jul 2020 12:29:58 -0700
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On 7/30/20 12:20 PM, Peilin Ye wrote:
> rds_notify_queue_get() is potentially copying uninitialized kernel stack
> memory to userspace since the compiler may leave a 4-byte hole at the end
> of `cmsg`.
> 
> In 2016 we tried to fix this issue by doing `= { 0 };` on `cmsg`, which
> unfortunately does not always initialize that 4-byte hole. Fix it by using
> memset() instead.
> 
> Cc: stable@vger.kernel.org
> Fixes: f037590fff30 ("rds: fix a leak of kernel memory")
> Fixes: bdbe6fbc6a2f ("RDS: recv.c")
> Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
> Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
> ---
> Note: the "real" copy_to_user() happens in put_cmsg(), where
> `cmlen - sizeof(*cm)` equals to `sizeof(cmsg)`.
> 
> Reference: https://lwn.net/Articles/417989/
> 
> $ pahole -C "rds_rdma_notify" net/rds/recv.o
> struct rds_rdma_notify {
> 	__u64                      user_token;           /*     0     8 */
> 	__s32                      status;               /*     8     4 */
> 
> 	/* size: 16, cachelines: 1, members: 2 */
> 	/* padding: 4 */
> 	/* last cacheline: 16 bytes */
> };
> 
>   net/rds/recv.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
Looks good.
FWIW,
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>