[Linux-kernel-mentees] [PATCH net] rds: Prevent kernel-infoleak in rds_notify_queue_get()

[santosh.shilimkar at oracle.com]

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 at vger.kernel.org
> Fixes: f037590fff30 ("rds: fix a leak of kernel memory")
> Fixes: bdbe6fbc6a2f ("RDS: recv.c")
> Suggested-by: Dan Carpenter <dan.carpenter at oracle.com>
> Signed-off-by: Peilin Ye <yepeilin.cs at 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 at oracle.com>