linux-kernel - 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

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Message-ID: <03cb97b4-c58a-42fc-aaea-db63c1b2ce4b@kernel.org>
Date: Mon, 6 Oct 2025 13:23:48 -0600
From: Khalid Aziz <khalid@...nel.org>
To: Kshitij Paranjape <kshitijvparanjape@...il.com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>
Cc: Doug Gilbert <dgilbert@...erlog.com>,
 "James E . J . Bottomley" <James.Bottomley@...senPartnership.com>,
 skhan@...uxfoundation.org, david.hunter.linux@...il.com,
 linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kernel-mentees@...ts.linux.dev, stable@...r.kernel.org,
 syzbot+270f1c719ee7baab9941@...kaller.appspotmail.com
Subject: 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.

On 10/6/25 11:46 AM, Kshitij Paranjape wrote:
> Cc: <stable@...r.kernel.org>
> Reported-by: syzbot+270f1c719ee7baab9941@...kaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=270f1c719ee7baab9941
> Signed-off-by: Kshitij Paranjape <kshitijvparanjape@...il.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