scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

[PATCH] scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

Posted by Kshitij Paranjape 2 months ago

Cc: <stable@vger.kernel.org>
Reported-by: syzbot+270f1c719ee7baab9941@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
Signed-off-by: Kshitij Paranjape <kshitijvparanjape@gmail.com>
---
 drivers/scsi/sg.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
index effb7e768165..9ae41bb256d7 100644
--- a/drivers/scsi/sg.c
+++ b/drivers/scsi/sg.c
@@ -1888,6 +1888,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
 		if (num < PAGE_SIZE) {
 			scatter_elem_sz = PAGE_SIZE;
 			scatter_elem_sz_prev = PAGE_SIZE;
+			num = scatter_elem_sz;
 		} else
 			scatter_elem_sz_prev = num;
 	}
-- 
2.43.0

Re: [PATCH] scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

Posted by David Hunter 2 months ago

On 10/6/25 13:46, Kshitij Paranjape wrote:
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+270f1c719ee7baab9941@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
> Signed-off-by: Kshitij Paranjape <kshitijvparanjape@gmail.com>

Hey Kshitij,

the formatting didn't quite work out the way you intended. For the next
version, please try to send it to Shuah and I first.

Re: [PATCH] scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

Posted by Khalid Aziz 2 months ago

On 10/6/25 11:46 AM, Kshitij Paranjape wrote:
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+270f1c719ee7baab9941@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
> Signed-off-by: Kshitij Paranjape <kshitijvparanjape@gmail.com>
> ---
>   drivers/scsi/sg.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index effb7e768165..9ae41bb256d7 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1888,6 +1888,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
>   		if (num < PAGE_SIZE) {
>   			scatter_elem_sz = PAGE_SIZE;
>   			scatter_elem_sz_prev = PAGE_SIZE;
> +			num = scatter_elem_sz;
>   		} else
>   			scatter_elem_sz_prev = num;
>   	}

Have you seen any issues caused by not setting num to PAGE_SIZE when num 
< PAGE_SIZE?

 From what I can see, num is used to calculate the page order for 
allocation which will be 0 whether num=PAGE_SIZE or < PAGE_SIZE. After 
that num gets assigned a new value any way before its next use.

--
Khalid

Re: [PATCH] scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

Posted by Khalid Aziz 2 months ago

On 10/6/25 11:46 AM, Kshitij Paranjape wrote:
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+270f1c719ee7baab9941@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
> Signed-off-by: Kshitij Paranjape <kshitijvparanjape@gmail.com>
> ---
>   drivers/scsi/sg.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index effb7e768165..9ae41bb256d7 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1888,6 +1888,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
>   		if (num < PAGE_SIZE) {
>   			scatter_elem_sz = PAGE_SIZE;
>   			scatter_elem_sz_prev = PAGE_SIZE;
> +			num = scatter_elem_sz;
>   		} else
>   			scatter_elem_sz_prev = num;
>   	}

Please add a one line summary above your commit log to avoid the issue 
Vivek pointed out. One line summary will become the subject line for 
your patch email.

--
Khalid

Re: [PATCH] scsi: fix shift out-of-bounds in sg_build_indirect The num variable is set to 0. The variable num gets its value from scatter_elem_sz. However the minimum value of scatter_elem_sz is PAGE_SHIFT. So setting num to PAGE_SIZE when num < PAGE_SIZE.

Posted by vivek yadav 2 months ago

Hi Kshitij,

Subject line of your patch should not exceed more than 80 characters
[recommended]
Please check your patch format.

~~vivek

On Mon, Oct 6, 2025 at 11:17 PM Kshitij Paranjape
<kshitijvparanjape@gmail.com> wrote:
>
> Cc: <stable@vger.kernel.org>
> Reported-by: syzbot+270f1c719ee7baab9941@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
> Signed-off-by: Kshitij Paranjape <kshitijvparanjape@gmail.com>
> ---
>  drivers/scsi/sg.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index effb7e768165..9ae41bb256d7 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -1888,6 +1888,7 @@ sg_build_indirect(Sg_scatter_hold * schp, Sg_fd * sfp, int buff_size)
>                 if (num < PAGE_SIZE) {
>                         scatter_elem_sz = PAGE_SIZE;
>                         scatter_elem_sz_prev = PAGE_SIZE;
> +                       num = scatter_elem_sz;
>                 } else
>                         scatter_elem_sz_prev = num;
>         }
> --
> 2.43.0
>
>