Re: [PATCH net 2/2] net/smc: Don't use RMBs not mapped to new link in SMCRv2 ADD LINK

From: Wenjia Zhang
Date: Sat May 27 2023 - 06:23:23 EST

On 26.05.23 13:49, Wen Gu wrote:
We encountered a crash when using SMCRv2. It is caused by a logical
error in smc_llc_fill_ext_v2().

BUG: kernel NULL pointer dereference, address: 0000000000000014
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP PTI
CPU: 7 PID: 453 Comm: kworker/7:4 Kdump: loaded Tainted: G W E 6.4.0-rc3+ #44
Workqueue: events smc_llc_add_link_work [smc]
RIP: 0010:smc_llc_fill_ext_v2+0x117/0x280 [smc]
RSP: 0018:ffffacb5c064bd88 EFLAGS: 00010282
RAX: ffff9a6bc1c3c02c RBX: ffff9a6be3558000 RCX: 0000000000000000
RDX: 0000000000000002 RSI: 0000000000000002 RDI: 000000000000000a
RBP: ffffacb5c064bdb8 R08: 0000000000000040 R09: 000000000000000c
R10: ffff9a6bc0910300 R11: 0000000000000002 R12: 0000000000000000
R13: 0000000000000002 R14: ffff9a6bc1c3c02c R15: ffff9a6be3558250
FS: 0000000000000000(0000) GS:ffff9a6eefdc0000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000014 CR3: 000000010b078003 CR4: 00000000003706e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
smc_llc_send_add_link+0x1ae/0x2f0 [smc]
smc_llc_srv_add_link+0x2c9/0x5a0 [smc]
? cc_mkenc+0x40/0x60
smc_llc_add_link_work+0xb8/0x140 [smc]
? __pfx_worker_thread+0x10/0x10
? __pfx_kthread+0x10/0x10

When an alernate RNIC is available in system, SMC will try to add a new
link based on the RNIC for resilience. All the RMBs in use will be mapped
to the new link. Then the RMBs' MRs corresponding to the new link will be
filled into SMCRv2 LLC ADD LINK messages.

However, smc_llc_fill_ext_v2() mistakenly accesses to unused RMBs which
haven't been mapped to the new link and have no valid MRs, thus causing
a crash. So this patch fixes the logic.

Fixes: b4ba4652b3f8 ("net/smc: extend LLC layer for SMC-Rv2")
Signed-off-by: Wen Gu <guwen@xxxxxxxxxxxxxxxxx>
net/smc/smc_llc.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
index 8423e8e..7a8d916 100644
--- a/net/smc/smc_llc.c
+++ b/net/smc/smc_llc.c
@@ -617,6 +617,8 @@ static int smc_llc_fill_ext_v2(struct smc_llc_msg_add_link_v2_ext *ext,
goto out;
buf_pos = smc_llc_get_first_rmb(lgr, &buf_lst);
for (i = 0; i < ext->num_rkeys; i++) {
+ while (buf_pos && !(buf_pos)->used)
+ buf_pos = smc_llc_get_next_rmb(lgr, &buf_lst, buf_pos);
if (!buf_pos)
rmb = buf_pos;
@@ -626,8 +628,6 @@ static int smc_llc_fill_ext_v2(struct smc_llc_msg_add_link_v2_ext *ext,
cpu_to_be64((uintptr_t)rmb->cpu_addr) :
buf_pos = smc_llc_get_next_rmb(lgr, &buf_lst, buf_pos);
- while (buf_pos && !(buf_pos)->used)
- buf_pos = smc_llc_get_next_rmb(lgr, &buf_lst, buf_pos);
len += i * sizeof(ext->rt[0]);

I'm wondering if this crash is introduced by the first fix patch you wrote.