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Fri, 20 Mar 2026 23:23:19 -0700 (PDT) Received: from localhost ([2408:8642:893:d2da:92d:9d57:dad5:f19e]) by smtp.gmail.com with UTF8SMTPSA id 98e67ed59e1d1-35bc5ed0777sm7062505a91.0.2026.03.20.23.23.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 Mar 2026 23:23:19 -0700 (PDT) From: yuhaocheng035@gmail.com To: Greg Kroah-Hartman , Jiri Slaby Cc: Nicolas Pitre , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Calixte Pernot Subject: [PATCH] tty: vt: Fix slab-out-of-bounds write in do_con_write Date: Sat, 21 Mar 2026 14:23:12 +0800 Message-ID: <20260321062312.4290-1-yuhaocheng035@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Haocheng Yu A KASAN: slab-out-of-bounds Write in do_con_write issue is reported by=20 a modified Syzkaller-based kernel fuzzing tool that we developed. The=20 report indicates the problem lies in vc_con_write_normal=20 drivers/tty/vt/vt.c:3141(scr_writew(tc, (u16*)vc->vc_pos)), which writes=20 2 bytes to the right of the allocated region at 2634 bytes. Since it did not provide any repro program or enough information,=20 the cause remains unclear. However, adding a validity check of vc->vc_pos=20 before scr_writew should avoid this issue. Signed-off-by: Haocheng Yu --- drivers/tty/vt/vt.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index 6e0089b85c27..95d860f09837 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3138,6 +3138,13 @@ static int vc_con_write_normal(struct vc_data *vc, i= nt tc, int c, (tc & 0xff); tc |=3D (vc_attr << 8) & ~himask; =20 + unsigned long end =3D vc->vc_origin + vc->vc_screenbuf_size; + + if (WARN_ON_ONCE(vc->vc_screenbuf_size < 2 || + end < vc->vc_origin || + vc->vc_pos < vc->vc_origin || + vc->vc_pos > end - 2)) + return -1; + scr_writew(tc, (u16 *)vc->vc_pos); =20 if (con_should_update(vc) && draw->x < 0) { base-commit: 7d0a66e4bb9081d75c82ec4957c50034cb0ea449 --=20 2.51.0