linux-kernel - [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: <20251006174658.217497-1-kshitijvparanjape@gmail.com>
Date: Mon,  6 Oct 2025 23:16:58 +0530
From: Kshitij Paranjape <kshitijvparanjape@...il.com>
To: "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,
	khalid@...nel.org,
	linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev,
	Kshitij Paranjape <kshitijvparanjape@...il.com>,
	stable@...r.kernel.org,
	syzbot+270f1c719ee7baab9941@...kaller.appspotmail.com
Subject: [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.

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;
 	}
-- 
2.43.0