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@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