Re: [PATCH net v6 1/3] net/smc: fix use-after-free of the LLC qentry in smc_llc_srv_add_link()

[Sidraya Jayagond <sidraya@linux.ibm.com>]

On 12/08/26 4:49 am, Yehyeong Lee wrote:
> smc_llc_srv_add_link() keeps add_llc pointing into the queue entry:
> 
>   add_llc = &qentry->msg.add_link;			smc_llc.c:1482
>   ...
>   smc_llc_save_add_link_info(link_new, add_llc);	smc_llc.c:1494
>   smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);		smc_llc.c:1495
>   ...
>   u8 *llc_msg = smc_link_shared_v2_rxbuf(link) ?
> 	(u8 *)lgr->wr_rx_buf_v2 : (u8 *)add_llc;	smc_llc.c:1504
>   smc_llc_save_add_link_rkeys(link, link_new, llc_msg);	smc_llc.c:1506
> 
> smc_llc_flow_qentry_del() kfree()s the entry, so on a link without a shared
> v2 receive buffer the pointer handed to smc_llc_save_add_link_rkeys() is
> already freed.  Before the Fixes: commit that branch always used
> lgr->wr_rx_buf_v2 and add_llc was not used after the free.
> 
> Reproduced on an unpatched tree over rxe, with KASAN, kasan_multi_shot
> and a link forced to max_recv_sge == 1: the entry is freed and read by
> the same call, and the freeing frame is smc_llc_srv_add_link() itself.
> 
>   [    2.523161] BUG: KASAN: slab-use-after-free in smc_llc_save_add_link_rkeys+0x333/0x350
>   [    2.523499] Read of size 2 at addr ffff8880052194de by task kworker/0:1/11
>   [    2.523789] 
>   [    2.523862] CPU: 0 UID: 0 PID: 11 Comm: kworker/0:1 Not tainted 7.2.0-rc5-p0-g2c9dd296545d #35 PREEMPT(lazy) 
>   [    2.523865] Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
>   [    2.523866] Workqueue: smc_hs_wq smc_listen_work
>   [    2.523869] Call Trace:
>   [    2.523870]  <TASK>
>   [    2.523871]  dump_stack_lvl+0x53/0x70
>   [    2.523872]  print_report+0xd0/0x630
>   [    2.523874]  ? __pfx__raw_spin_lock_irqsave+0x10/0x10
>   [    2.523876]  ? smc_llc_save_add_link_rkeys+0x333/0x350
>   [    2.523878]  kasan_report+0xce/0x100
>   [    2.523879]  ? smc_llc_save_add_link_rkeys+0x333/0x350
>   [    2.523881]  smc_llc_save_add_link_rkeys+0x333/0x350
>   [    2.523883]  ? smcr_buf_reg_lgr+0x2a4/0x660
>   [    2.523885]  smc_llc_srv_add_link+0xaa2/0x1e50
>   [    2.523888]  ? _printk+0xba/0xf0
>   [    2.523897]  ? __pfx_smc_llc_srv_add_link+0x10/0x10
>   [    2.523899]  ? down_write+0xb0/0x130
>   [    2.523903]  ? __pfx_down_write+0x10/0x10
>   [    2.523905]  smc_listen_work+0x489e/0x4d00
>   [    2.523907]  ? kmem_cache_free+0x1c6/0x3a0
>   [    2.523911]  ? __pfx_smc_listen_work+0x10/0x10
>   [    2.523913]  ? release_sock+0x148/0x1d0
>   [    2.523915]  ? smc_tcp_listen_work+0xb4f/0xfc0
>   [    2.523917]  ? _raw_spin_lock_irq+0x80/0xe0
>   [    2.523918]  ? __pfx__raw_spin_lock_irq+0x10/0x10
>   [    2.523920]  process_one_work+0x633/0x1030
>   [    2.523922]  ? assign_work+0x11d/0x370
>   [    2.523924]  worker_thread+0x45b/0xd10
>   [    2.523926]  ? __pfx_worker_thread+0x10/0x10
>   [    2.523928]  ? __pfx_worker_thread+0x10/0x10
>   [    2.523929]  kthread+0x2c6/0x3b0
>   [    2.523931]  ? recalc_sigpending+0x15c/0x1e0
>   [    2.523934]  ? __pfx_kthread+0x10/0x10
>   [    2.523935]  ret_from_fork+0x36e/0x5a0
>   [    2.523937]  ? __pfx_ret_from_fork+0x10/0x10
>   [    2.523938]  ? __switch_to+0x572/0xdd0
>   [    2.523943]  ? __pfx_kthread+0x10/0x10
>   [    2.523944]  ret_from_fork_asm+0x1a/0x30
>   [    2.523947]  </TASK>
>   [    2.523948] 
>   [    2.531253] Allocated by task 48:
>   [    2.531399]  kasan_save_stack+0x33/0x60
>   [    2.531570]  kasan_save_track+0x14/0x30
>   [    2.531737]  __kasan_kmalloc+0x8f/0xa0
>   [    2.531905]  __kmalloc_cache_noprof+0x158/0x370
>   [    2.532100]  smc_llc_enqueue+0x72/0x560
>   [    2.532268]  smc_wr_rx_tasklet_fn+0x474/0xa80
>   [    2.532491]  tasklet_action_common+0x20f/0x8a0
>   [    2.532714]  handle_softirqs+0x18e/0x590
>   [    2.532886]  do_softirq+0x3b/0x60
>   [    2.533036]  __local_bh_enable_ip+0x61/0x70
>   [    2.533221]  __alloc_skb+0x732/0x890
>   [    2.533384]  rxe_init_packet+0x16b/0x4f0
>   [    2.533567]  prepare_ack_packet+0xb8/0x830
>   [    2.533760]  rxe_receiver+0x495/0x96e0
>   [    2.533933]  do_work+0x144/0x470
>   [    2.534078]  process_one_work+0x633/0x1030
>   [    2.534257]  worker_thread+0x45b/0xd10
>   [    2.534424]  kthread+0x2c6/0x3b0
>   [    2.534569]  ret_from_fork+0x36e/0x5a0
>   [    2.534737]  ret_from_fork_asm+0x1a/0x30
>   [    2.534907] 
>   [    2.534980] Freed by task 11:
>   [    2.535112]  kasan_save_stack+0x33/0x60
>   [    2.535279]  kasan_save_track+0x14/0x30
>   [    2.535444]  kasan_save_free_info+0x3b/0x60
>   [    2.535625]  __kasan_slab_free+0x43/0x70
>   [    2.535798]  kfree+0x121/0x380
>   [    2.535935]  smc_llc_srv_add_link+0x9a8/0x1e50
>   [    2.536128]  smc_listen_work+0x489e/0x4d00
>   [    2.536305]  process_one_work+0x633/0x1030
>   [    2.536482]  worker_thread+0x45b/0xd10
>   [    2.536652]  kthread+0x2c6/0x3b0
>   [    2.536794]  ret_from_fork+0x36e/0x5a0
>   [    2.536958]  ret_from_fork_asm+0x1a/0x30
>   [    2.537133] 
>   [    2.537205] The buggy address belongs to the object at ffff888005219480
>   [    2.537205]  which belongs to the cache kmalloc-96 of size 96
>   [    2.537719] The buggy address is located 94 bytes inside of
>   [    2.537719]  freed 96-byte region [ffff888005219480, ffff8880052194e0)
>   [    2.538216] 
>   [    2.538289] The buggy address belongs to the physical page:
>   [    2.538524] page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5219
>   [    2.538857] flags: 0x100000000000000(node=0|zone=1)
>   [    2.539066] page_type: f5(slab)
>   [    2.539210] raw: 0100000000000000 ffff888001041280 dead000000000122 0000000000000000
>   [    2.539534] raw: 0000000000000000 0000000000200020 00000000f5000000 0000000000000000
>   [    2.539863] page dumped because: kasan: bad access detected
>   [    2.540098] 
>   [    2.540170] Memory state around the buggy address:
>   [    2.540379]  ffff888005219380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   [    2.540684]  ffff888005219400: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>   [    2.540988] >ffff888005219480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>   [    2.541291]                                                     ^
>   [    2.541548]  ffff888005219500: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
>   [    2.541857]  ffff888005219580: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
> 
> The offset is past the 72-byte queue entry because the out-of-bounds read
> fixed by the next patch is on the same line; what this patch removes is the
> free at smc_llc_srv_add_link+0x9a8 happening before the read at +0xaa2.
> 
> Detach the entry instead of freeing it there, and free it at the single
> exit label.  The reject path has to detach as well, otherwise it would be
> freed twice.
> 
> This changes only the lifetime of the entry.  The same read still runs past
> its end until the next two patches bound it, so a backport wants all three.
> 
> Fixes: 27ef6a9981fe ("net/smc: support SMC-R V2 for rdma devices with max_recv_sge equals to 1")
> Cc: stable@vger.kernel.org
> Signed-off-by: Yehyeong Lee <yhlee@isslab.korea.ac.kr>
> ---
> Changes since v5: return through the existing exit label.
> 
>  net/smc/smc_llc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/net/smc/smc_llc.c b/net/smc/smc_llc.c
> index 954b2ff1815c..055a03eee5b5 100644
> --- a/net/smc/smc_llc.c
> +++ b/net/smc/smc_llc.c
> @@ -1481,7 +1481,7 @@ int smc_llc_srv_add_link(struct smc_link *link,
>  	}
>  	add_llc = &qentry->msg.add_link;
>  	if (add_llc->hd.flags & SMC_LLC_FLAG_ADD_LNK_REJ) {
> -		smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);
> +		smc_llc_flow_qentry_clr(&lgr->llc_flow_lcl);
>  		rc = -ENOLINK;
>  		goto out_err;
>  	}
> @@ -1492,7 +1492,8 @@ int smc_llc_srv_add_link(struct smc_link *link,
>  		lgr_new_t = SMC_LGR_ASYMMETRIC_PEER;
>  	}
>  	smc_llc_save_add_link_info(link_new, add_llc);
> -	smc_llc_flow_qentry_del(&lgr->llc_flow_lcl);
> +	/* add_llc still points into qentry, so only detach it here */
> +	smc_llc_flow_qentry_clr(&lgr->llc_flow_lcl);
>  
>  	rc = smc_ib_ready_link(link_new);
>  	if (rc)
> @@ -1512,14 +1513,14 @@ int smc_llc_srv_add_link(struct smc_link *link,
>  	rc = smc_llc_srv_conf_link(link, link_new, lgr_new_t);
>  	if (rc)
>  		goto out_err;
> -	kfree(ini);
> -	return 0;
> +	goto out;
>  out_err:
>  	if (link_new) {
>  		link_new->state = SMC_LNK_INACTIVE;
>  		smcr_link_clear(link_new, false);
>  	}
>  out:
> +	kfree(qentry);
>  	kfree(ini);
>  	if (send_req_add_link_resp)
>  		smc_llc_send_req_add_link_response(req_qentry);

Reviewed-by: Sidraya Jayagond <sidraya@linux.ibm.com>