linux-kernel - [PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address

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Message-Id: <1762370746-6304-1-git-send-email-hamzamahfooz@linux.microsoft.com>
Date: Wed,  5 Nov 2025 11:25:46 -0800
From: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
To: linux-kernel@...r.kernel.org
Cc: "Martin K. Petersen" <martin.petersen@...cle.com>,
	Guixin Liu <kanie@...ux.alibaba.com>,
	Nicholas Bellinger <nab@...ux-iscsi.org>,
	Sheng Yang <sheng@...ker.org>,
	linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org,
	Allen Pais <apais@...ux.microsoft.com>,
	Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>,
	stable@...r.kernel.org
Subject: [PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address_show()

If the allocation of tl_hba->sh fails in tcm_loop_driver_probe() and we
attempt to dereference it in tcm_loop_tpg_address_show() we will get a
segfault, see below for an example. So, check tl_hba->sh before
dereferencing it.

  Unable to allocate struct scsi_host
  BUG: kernel NULL pointer dereference, address: 0000000000000194
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  PGD 0 P4D 0
  Oops: 0000 [#1] PREEMPT SMP NOPTI
  CPU: 1 PID: 8356 Comm: tokio-runtime-w Not tainted 6.6.104.2-4.azl3 #1
  Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.1 09/28/2024
  RIP: 0010:tcm_loop_tpg_address_show+0x2e/0x50 [tcm_loop]
...
  Call Trace:
   <TASK>
   configfs_read_iter+0x12d/0x1d0 [configfs]
   vfs_read+0x1b5/0x300
   ksys_read+0x6f/0xf0
...

Cc: stable@...r.kernel.org
Fixes: 2628b352c3d4 ("tcm_loop: Show address of tpg in configfs")
Signed-off-by: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
---
 drivers/target/loopback/tcm_loop.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/target/loopback/tcm_loop.c b/drivers/target/loopback/tcm_loop.c
index c7b7da629741..01a8e349dc4d 100644
--- a/drivers/target/loopback/tcm_loop.c
+++ b/drivers/target/loopback/tcm_loop.c
@@ -894,6 +894,9 @@ static ssize_t tcm_loop_tpg_address_show(struct config_item *item,
 			struct tcm_loop_tpg, tl_se_tpg);
 	struct tcm_loop_hba *tl_hba = tl_tpg->tl_hba;

+	if (!tl_hba->sh)
+		return -ENODEV;
+
 	return snprintf(page, PAGE_SIZE, "%d:0:%d\n",
 			tl_hba->sh->host_no, tl_tpg->tl_tpgt);
 }
-- 
2.49.0