Re: [PATCH net] net/smc: Fix possible access to freed memory in link clear

From: Tony Lu
Date: Mon Aug 29 2022 - 12:39:03 EST

On Mon, Aug 29, 2022 at 10:54:35PM +0800, liuyacan@xxxxxxxxxxxxxxxx wrote:
> From: liuyacan <liuyacan@xxxxxxxxxxxxxxxx>
>
> After modifying the QP to the Error state, all RX WR would be
> completed with WC in IB_WC_WR_FLUSH_ERR status. Current
> implementation does not wait for it is done, but free the link
> directly. So there is a risk that accessing the freed link in
> tasklet context.
>
> Here is a crash example:
>
> BUG: unable to handle page fault for address: ffffffff8f220860
> #PF: supervisor write access in kernel mode
> #PF: error_code(0x0002) - not-present page
> PGD f7300e067 P4D f7300e067 PUD f7300f063 PMD 8c4e45063 PTE 800ffff08c9df060
> Oops: 0002 [#1] SMP PTI
> CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: G S OE 5.10.0-0607+ #23
> Hardware name: Inspur NF5280M4/YZMB-00689-101, BIOS 4.1.20 07/09/2018
> RIP: 0010:native_queued_spin_lock_slowpath+0x176/0x1b0
> Code: f3 90 48 8b 32 48 85 f6 74 f6 eb d5 c1 ee 12 83 e0 03 83 ee 01 48 c1 e0 05 48 63 f6 48 05 00 c8 02 00 48 03 04 f5 00 09 98 8e <48> 89 10 8b 42 08 85 c0 75 09 f3 90 8b 42 08 85 c0 74 f7 48 8b 32
> RSP: 0018:ffffb3b6c001ebd8 EFLAGS: 00010086
> RAX: ffffffff8f220860 RBX: 0000000000000246 RCX: 0000000000080000
> RDX: ffff91db1f86c800 RSI: 000000000000173c RDI: ffff91db62bace00
> RBP: ffff91db62bacc00 R08: 0000000000000000 R09: c00000010000028b
> R10: 0000000000055198 R11: ffffb3b6c001ea58 R12: ffff91db80e05010
> R13: 000000000000000a R14: 0000000000000006 R15: 0000000000000040
> FS: 0000000000000000(0000) GS:ffff91db1f840000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffffff8f220860 CR3: 00000001f9580004 CR4: 00000000003706e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <IRQ>
> _raw_spin_lock_irqsave+0x30/0x40
> mlx5_ib_poll_cq+0x4c/0xc50 [mlx5_ib]
> smc_wr_rx_tasklet_fn+0x56/0xa0 [smc]
> tasklet_action_common.isra.21+0x66/0x100
> __do_softirq+0xd5/0x29c
> asm_call_irq_on_stack+0x12/0x20
> </IRQ>
> do_softirq_own_stack+0x37/0x40
> irq_exit_rcu+0x9d/0xa0
> sysvec_call_function_single+0x34/0x80
> asm_sysvec_call_function_single+0x12/0x20
>
> Signed-off-by: liuyacan <liuyacan@xxxxxxxxxxxxxxxx>
> ---
> net/smc/smc_core.c | 2 ++
> net/smc/smc_core.h | 2 ++
> net/smc/smc_wr.c | 12 ++++++++++++
> net/smc/smc_wr.h | 3 +++
> 4 files changed, 19 insertions(+)
>
> diff --git a/net/smc/smc_core.c b/net/smc/smc_core.c
> index ff49a11f5..b632a33f1 100644
> --- a/net/smc/smc_core.c
> +++ b/net/smc/smc_core.c
> @@ -752,6 +752,7 @@ int smcr_link_init(struct smc_link_group *lgr, struct smc_link *lnk,
> atomic_inc(&lnk->smcibdev->lnk_cnt);
> refcount_set(&lnk->refcnt, 1); /* link refcnt is set to 1 */
> lnk->clearing = 0;
> + lnk->rx_drained = 0;
> lnk->path_mtu = lnk->smcibdev->pattr[lnk->ibport - 1].active_mtu;
> lnk->link_id = smcr_next_link_id(lgr);
> lnk->lgr = lgr;
> @@ -1269,6 +1270,7 @@ void smcr_link_clear(struct smc_link *lnk, bool log)
> smcr_buf_unmap_lgr(lnk);
> smcr_rtoken_clear_link(lnk);
> smc_ib_modify_qp_error(lnk);
> + smc_wr_drain_cq(lnk);
> smc_wr_free_link(lnk);
> smc_ib_destroy_queue_pair(lnk);
> smc_ib_dealloc_protection_domain(lnk);
> diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
> index fe8b524ad..0a469a3e7 100644
> --- a/net/smc/smc_core.h
> +++ b/net/smc/smc_core.h
> @@ -117,6 +117,7 @@ struct smc_link {
> u64 wr_rx_id; /* seq # of last recv WR */
> u32 wr_rx_cnt; /* number of WR recv buffers */
> unsigned long wr_rx_tstamp; /* jiffies when last buf rx */
> + wait_queue_head_t wr_rx_drain_wait; /* wait for WR drain */
>
> struct ib_reg_wr wr_reg; /* WR register memory region */
> wait_queue_head_t wr_reg_wait; /* wait for wr_reg result */
> @@ -138,6 +139,7 @@ struct smc_link {
> u8 link_idx; /* index in lgr link array */
> u8 link_is_asym; /* is link asymmetric? */
> u8 clearing : 1; /* link is being cleared */
> + u8 rx_drained : 1; /* link is drained */
> refcount_t refcnt; /* link reference count */
> struct smc_link_group *lgr; /* parent link group */
> struct work_struct link_down_wrk; /* wrk to bring link down */
> diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
> index 26f8f240d..f9992896a 100644
> --- a/net/smc/smc_wr.c
> +++ b/net/smc/smc_wr.c
> @@ -465,6 +465,10 @@ static inline void smc_wr_rx_process_cqes(struct ib_wc wc[], int num)
> case IB_WC_RNR_RETRY_EXC_ERR:
> case IB_WC_WR_FLUSH_ERR:
> smcr_link_down_cond_sched(link);
> + if (link->clearing && wc[i]->wr_id == link->wr_rx_id) {
> + link->rx_drained = 1;
> + wake_up(&link->wr_rx_drain_wait);
> + }

I am wondering if we should wait for all the wc comes back?

> break;
> default:
> smc_wr_rx_post(link); /* refill WR RX */
> @@ -631,6 +635,13 @@ static void smc_wr_init_sge(struct smc_link *lnk)
> lnk->wr_reg.access = IB_ACCESS_LOCAL_WRITE | IB_ACCESS_REMOTE_WRITE;
> }
>
> +void smc_wr_drain_cq(struct smc_link *lnk)
> +{
> + wait_event_interruptible_timeout(lnk->wr_rx_drain_wait,
> + (lnk->drained == 1),
> + SMC_WR_RX_WAIT_DRAIN_TIME);
> +}

Should we wait for it with timeout? It should eventually be wake up
normally before freeing link. Waiting for SMC_WR_RX_WAIT_DRAIN_TIME (2s)
may also have this issue, although the probability of occurrence is
greatly reduced.

Cheers,
Tony Lu

> +
> void smc_wr_free_link(struct smc_link *lnk)
> {
> struct ib_device *ibdev;
> @@ -889,6 +900,7 @@ int smc_wr_create_link(struct smc_link *lnk)
> atomic_set(&lnk->wr_tx_refcnt, 0);
> init_waitqueue_head(&lnk->wr_reg_wait);
> atomic_set(&lnk->wr_reg_refcnt, 0);
> + init_waitqueue_head(&lnk->wr_rx_drain_wait);
> return rc;
>
> dma_unmap:
> diff --git a/net/smc/smc_wr.h b/net/smc/smc_wr.h
> index a54e90a11..2a7ebdba3 100644
> --- a/net/smc/smc_wr.h
> +++ b/net/smc/smc_wr.h
> @@ -27,6 +27,8 @@
>
> #define SMC_WR_TX_PEND_PRIV_SIZE 32
>
> +#define SMC_WR_RX_WAIT_DRAIN_TIME (2 * HZ)
> +
> struct smc_wr_tx_pend_priv {
> u8 priv[SMC_WR_TX_PEND_PRIV_SIZE];
> };
> @@ -101,6 +103,7 @@ static inline int smc_wr_rx_post(struct smc_link *link)
> int smc_wr_create_link(struct smc_link *lnk);
> int smc_wr_alloc_link_mem(struct smc_link *lnk);
> int smc_wr_alloc_lgr_mem(struct smc_link_group *lgr);
> +void smc_wr_drain_cq(struct smc_link *lnk);
> void smc_wr_free_link(struct smc_link *lnk);
> void smc_wr_free_link_mem(struct smc_link *lnk);
> void smc_wr_free_lgr_mem(struct smc_link_group *lgr);
> --
> 2.20.1