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

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Message-Id: <C4A5B08B-27E4-4ACF-96E4-9351F0BFF320@linux.microsoft.com>
Date: Thu, 6 Nov 2025 07:56:24 -0800
From: Allen Pais <apais@...ux.microsoft.com>
To: Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com>
Cc: linux-kernel@...r.kernel.org,
 "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,
 stable@...r.kernel.org
Subject: Re: [PATCH] scsi: target: tcm_loop: fix segfault in
 tcm_loop_tpg_address_show()



> On Nov 5, 2025, at 11:25 AM, Hamza Mahfooz <hamzamahfooz@...ux.microsoft.com> wrote:
> 
> 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>

Reviewed-by: Allen Pais <apais@...ux.microsoft.com <mailto:apais@...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