Hi Leon,
Thanks for taking the time to review.
Please find my comments inline -
On 6/9/20 12:00 AM, Leon Romanovsky wrote:
> On Mon, Jun 08, 2020 at 07:46:16AM -0700, Divya Indi wrote:
>> Commit 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list before sending")'
>> -
>> 1. Adds the query to the request list before ib_nl_snd_msg.
>> 2. Removes ib_nl_send_msg from within the spinlock which also makes it
>> possible to allocate memory with GFP_KERNEL.
>>
>> However, if there is a delay in sending out the request (For
>> eg: Delay due to low memory situation) the timer to handle request timeout
>> might kick in before the request is sent out to ibacm via netlink.
>> ib_nl_request_timeout may release the query causing a use after free situation
>> while accessing the query in ib_nl_send_msg.
>>
>> Call Trace for the above race:
>>
>> [<ffffffffa02f43cb>] ? ib_pack+0x17b/0x240 [ib_core]
>> [<ffffffffa032aef1>] ib_sa_path_rec_get+0x181/0x200 [ib_sa]
>> [<ffffffffa0379db0>] rdma_resolve_route+0x3c0/0x8d0 [rdma_cm]
>> [<ffffffffa0374450>] ? cma_bind_port+0xa0/0xa0 [rdma_cm]
>> [<ffffffffa040f850>] ? rds_rdma_cm_event_handler_cmn+0x850/0x850
>> [rds_rdma]
>> [<ffffffffa040f22c>] rds_rdma_cm_event_handler_cmn+0x22c/0x850
>> [rds_rdma]
>> [<ffffffffa040f860>] rds_rdma_cm_event_handler+0x10/0x20 [rds_rdma]
>> [<ffffffffa037778e>] addr_handler+0x9e/0x140 [rdma_cm]
>> [<ffffffffa026cdb4>] process_req+0x134/0x190 [ib_addr]
>> [<ffffffff810a02f9>] process_one_work+0x169/0x4a0
>> [<ffffffff810a0b2b>] worker_thread+0x5b/0x560
>> [<ffffffff810a0ad0>] ? flush_delayed_work+0x50/0x50
>> [<ffffffff810a68fb>] kthread+0xcb/0xf0
>> [<ffffffff816ec49a>] ? __schedule+0x24a/0x810
>> [<ffffffff816ec49a>] ? __schedule+0x24a/0x810
>> [<ffffffff810a6830>] ? kthread_create_on_node+0x180/0x180
>> [<ffffffff816f25a7>] ret_from_fork+0x47/0x90
>> [<ffffffff810a6830>] ? kthread_create_on_node+0x180/0x180
>> ....
>> RIP [<ffffffffa03296cd>] send_mad+0x33d/0x5d0 [ib_sa]
>>
>> To resolve the above issue -
>> 1. Add the req to the request list only after the request has been sent out.
>> 2. To handle the race where response comes in before adding request to
>> the request list, send(rdma_nl_multicast) and add to list while holding the
>> spinlock - request_lock.
>> 3. Use GFP_NOWAIT for rdma_nl_multicast since it is called while holding
>> a spinlock. In case of memory allocation failure, request will go out to SA.
>>
>> Signed-off-by: Divya Indi <divya.indi@xxxxxxxxxx>
>> Fixes: 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list
>> before sending")
> Author SOB should be after "Fixes" line.
My bad. Noted.
>
>> ---
>> drivers/infiniband/core/sa_query.c | 34 +++++++++++++++++-----------------
>> 1 file changed, 17 insertions(+), 17 deletions(-)
>>
>> diff --git a/drivers/infiniband/core/sa_query.c b/drivers/infiniband/core/sa_query.c
>> index 74e0058..042c99b 100644
>> --- a/drivers/infiniband/core/sa_query.c
>> +++ b/drivers/infiniband/core/sa_query.c
>> @@ -836,6 +836,9 @@ static int ib_nl_send_msg(struct ib_sa_query *query, gfp_t gfp_mask)
>> void *data;
>> struct ib_sa_mad *mad;
>> int len;
>> + unsigned long flags;
>> + unsigned long delay;
>> + int ret;
>>
>> mad = query->mad_buf->mad;
>> len = ib_nl_get_path_rec_attrs_len(mad->sa_hdr.comp_mask);
>> @@ -860,35 +863,32 @@ static int ib_nl_send_msg(struct ib_sa_query *query, gfp_t gfp_mask)
>> /* Repair the nlmsg header length */
>> nlmsg_end(skb, nlh);
>>
>> - return rdma_nl_multicast(&init_net, skb, RDMA_NL_GROUP_LS, gfp_mask);
>> + spin_lock_irqsave(&ib_nl_request_lock, flags);
>> + ret = rdma_nl_multicast(&init_net, skb, RDMA_NL_GROUP_LS, GFP_NOWAIT);
> It is hard to be convinced that this is correct solution. The mix of
> gfp_flags and GFP_NOWAIT at the same time and usage of
> ib_nl_request_lock to protect lists and suddenly rdma_nl_multicast() too
> makes this code unreadable/non-maintainable.
Prior to 3ebd2fd0d011 ("IB/sa: Put netlink request into the request list
before sending"), we had ib_nl_send_msg under the spinlock ib_nl_request_lock.
ie we had -
1. Get spinlock - ib_nl_request_lock
2. ib_nl_send_msg
2.a) rdma_nl_multicast
3. Add request to the req list
4. Arm the timer if needed.
5. Release spinlock
However, ib_nl_send_msg involved a memory allocation using GFP_KERNEL.
hence, was moved out of the spinlock. In addition, req was now being
added prior to ib_nl_send_msg [To handle the race where response can
come in before we get a chance to add the request back to the list].
This introduced another race resulting in use-after-free.[Described in the commit.]
To resolve this, sending out the request and adding it to list need to
happen while holding the request_lock.
To ensure minimum allocations while holding the lock, instead of having
the entire ib_nl_send_msg under the lock, we only have rdma_nl_multicast
under this spinlock.
However, do you think it would be a good idea to split ib_nl_send_msg
into 2 functions -
1. Prepare the req/query [Outside the spinlock]
2. Sending the req - rdma_nl_multicast [while holding spinlock]
Would this be more intuitive?
>> + if (!ret) {
> Please use kernel coding style.
>
> if (ret) {
> spin_unlock_irqrestore(&ib_nl_request_lock, flags);
> return ret;
> }
>
> ....
Noted. Will make this change.
>
>> + /* Put the request on the list.*/
>> + delay = msecs_to_jiffies(sa_local_svc_timeout_ms);
>> + query->timeout = delay + jiffies;
>> + list_add_tail(&query->list, &ib_nl_request_list);
>> + /* Start the timeout if this is the only request */
>> + if (ib_nl_request_list.next == &query->list)
>> + queue_delayed_work(ib_nl_wq, &ib_nl_timed_work, delay);
>> + }
>> + spin_unlock_irqrestore(&ib_nl_request_lock, flags);
>> +
>> + return ret;
>> }
>>
>> static int ib_nl_make_request(struct ib_sa_query *query, gfp_t gfp_mask)
>> {
>> - unsigned long flags;
>> - unsigned long delay;
>> int ret;
>>
>> INIT_LIST_HEAD(&query->list);
>> query->seq = (u32)atomic_inc_return(&ib_nl_sa_request_seq);
>>
>> - /* Put the request on the list first.*/
>> - spin_lock_irqsave(&ib_nl_request_lock, flags);
>> - delay = msecs_to_jiffies(sa_local_svc_timeout_ms);
>> - query->timeout = delay + jiffies;
>> - list_add_tail(&query->list, &ib_nl_request_list);
>> - /* Start the timeout if this is the only request */
>> - if (ib_nl_request_list.next == &query->list)
>> - queue_delayed_work(ib_nl_wq, &ib_nl_timed_work, delay);
>> - spin_unlock_irqrestore(&ib_nl_request_lock, flags);
>> -
>> ret = ib_nl_send_msg(query, gfp_mask);
>> if (ret) {
>> ret = -EIO;
>> - /* Remove the request */
>> - spin_lock_irqsave(&ib_nl_request_lock, flags);
>> - list_del(&query->list);
>> - spin_unlock_irqrestore(&ib_nl_request_lock, flags);
>> }
> Brackets should be removed too.
Noted.
>> return ret;
>> --
>> 1.8.3.1
>>
