[PATCH] nvmet-fc: fix use-after-free in nvmet_fc_ls_create_connection()

[Yehyeong Lee]

nvmet_fc_ls_create_connection() looks up the association with
nvmet_fc_find_target_assoc(), which returns it with a reference held, and
drops that reference as soon as the target queue has been allocated.
iod->assoc is then dereferenced again by nvmet_fc_makeconnid() while
building the connection id.

The queue only borrows the pointer and takes no reference of its own.
Once the lookup reference is dropped the association is kept alive solely
by the reference taken when it was created, so a disconnect LS or a remote
port unregister running concurrently can free it before
nvmet_fc_makeconnid() reads it:

BUG: KASAN: slab-use-after-free in nvmet_fc_handle_ls_rqst_work (drivers/nvme/target/fc.c:193 drivers/nvme/target/fc.c:1841 drivers/nvme/target/fc.c:1995 drivers/nvme/target/fc.c:2021)
Read of size 8 at addr ffff888179f1b000 by task kworker/u9:2/1167

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
Workqueue: nvmet-wq nvmet_fc_handle_ls_rqst_work
Call Trace:
 <TASK>
 dump_stack_lvl (lib/dump_stack.c:94 lib/dump_stack.c:120)
 print_report (mm/kasan/report.c:378 mm/kasan/report.c:482)
 kasan_report (mm/kasan/report.c:595)
 nvmet_fc_handle_ls_rqst_work (drivers/nvme/target/fc.c:193 drivers/nvme/target/fc.c:1841 drivers/nvme/target/fc.c:1995 drivers/nvme/target/fc.c:2021)
 process_scheduled_works (kernel/workqueue.c:3322 kernel/workqueue.c:3405)
 worker_thread (kernel/workqueue.c:3486)
 kthread (kernel/kthread.c:436)
 ret_from_fork (archkernel/process.c:158)
 ret_from_fork_asm (arch/x86/entry/entry_64.S:245)
 </TASK>

Freed by task 1167 on cpu 0 at 405.998150s:
 kasan_save_track (mm/kasan/common.c:57 mm/kasan/common.c:78)
 kasan_save_free_info (mm/kasan/generic.c:584)
 __kasan_slab_free (mm/kasan/common.c:253 mm/kasan/common.c:285)
 kfree (include/linux/kasan.h:235 mm/slub.c:2705 mm/slub.c:6405 mm/slub.c:6720)
 nvmet_fc_handle_ls_rqst_work (drivers/nvme/target/fc.c:1808 drivers/nvme/target/fc.c:1995 drivers/nvme/target/fc.c:2021)
 process_scheduled_works (kernel/workqueue.c:3322 kernel/workqueue.c:3405)
 worker_thread (kernel/workqueue.c:3486)
 kthread (kernel/kthread.c:436)
 ret_from_fork (archkernel/process.c:158)
 ret_from_fork_asm (arch/x86/entry/entry_64.S:245)

The buggy address belongs to the object at ffff888179f1b000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 0 bytes inside of
 freed 2048-byte region [ffff888179f1b000, ffff888179f1b800)

Hold the lookup reference until the response has been built, and drop it
on the error path as well.

Reported-by: Shuangpeng Bai <shuangpeng.kernel at gmail.com>
Closes: https://lore.kernel.org/linux-nvme/20260731204504.2396434-1-shuangpeng.kernel@gmail.com
Fixes: c53432030d86 ("nvme-fabrics: Add target support for FC transport")
Cc: stable at vger.kernel.org
Signed-off-by: Yehyeong Lee <yhlee at isslab.korea.ac.kr>
---
 drivers/nvme/target/fc.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/target/fc.c b/drivers/nvme/target/fc.c
index 1b557775e033a..f3e80095d7d16 100644
--- a/drivers/nvme/target/fc.c
+++ b/drivers/nvme/target/fc.c
@@ -1796,9 +1796,6 @@ nvmet_fc_ls_create_connection(struct nvmet_fc_tgtport *tgtport,
 					be16_to_cpu(rqst->connect_cmd.sqsize));
 			if (!queue)
 				ret = VERR_QUEUE_ALLOC_FAIL;
-
-			/* release get taken in nvmet_fc_find_target_assoc */
-			nvmet_fc_tgt_a_put(iod->assoc);
 		}
 	}
 
@@ -1812,6 +1809,8 @@ nvmet_fc_ls_create_connection(struct nvmet_fc_tgtport *tgtport,
 					FCNVME_RJT_RC_INV_ASSOC :
 					FCNVME_RJT_RC_LOGIC,
 				FCNVME_RJT_EXP_NONE, 0);
+		if (iod->assoc)
+			nvmet_fc_tgt_a_put(iod->assoc);
 		return;
 	}
 
@@ -1833,6 +1832,9 @@ nvmet_fc_ls_create_connection(struct nvmet_fc_tgtport *tgtport,
 	acc->connectid.connection_id =
 			cpu_to_be64(nvmet_fc_makeconnid(iod->assoc,
 				be16_to_cpu(rqst->connect_cmd.qid)));
+
+	/* release get taken in nvmet_fc_find_target_assoc */
+	nvmet_fc_tgt_a_put(iod->assoc);
 }
 
 /*
-- 
2.43.0