[PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address_show()

[PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address_show()

[Hamza Mahfooz]

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@vger.kernel.org
Fixes: 2628b352c3d4 ("tcm_loop: Show address of tpg in configfs")
Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.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

Re: [PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address_show()

[Chaitanya Kulkarni]

On 11/5/25 11:25, Hamza Mahfooz 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@vger.kernel.org
> Fixes: 2628b352c3d4 ("tcm_loop: Show address of tpg in configfs")
> Signed-off-by: Hamza Mahfooz<hamzamahfooz@linux.microsoft.com>
> ---


indeed :-

  313 static int tcm_loop_driver_probe(struct device *dev)
  314 {
  315         struct tcm_loop_hba *tl_hba;
  316         struct Scsi_Host *sh;
  317         int error, host_prot;
  318
  319         tl_hba = to_tcm_loop_hba(dev);
  320
  321         sh = scsi_host_alloc(&tcm_loop_driver_template,
  322                         sizeof(struct tcm_loop_hba));
  323         if (!sh) {
  324                 pr_err("Unable to allocate struct scsi_host\n");
  325                 return -ENODEV;
  326         }
  327         tl_hba->sh = sh;


Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>

-ck

Re: [PATCH] scsi: target: tcm_loop: fix segfault in tcm_loop_tpg_address_show()

[Allen Pais]

> On Nov 5, 2025, at 11:25 AM, Hamza Mahfooz <hamzamahfooz@linux.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@vger.kernel.org
> Fixes: 2628b352c3d4 ("tcm_loop: Show address of tpg in configfs")
> Signed-off-by: Hamza Mahfooz <hamzamahfooz@linux.microsoft.com>

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