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Sat, 27 Sep 2025 00:50:30 -0700 (PDT) Received: from arch-box ([2607:fea8:54de:2200::9c5c]) by smtp.gmail.com with ESMTPSA id af79cd13be357-85c2737848csm415143585a.3.2025.09.27.00.50.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 27 Sep 2025 00:50:29 -0700 (PDT) From: Albin Babu Varghese To: Simona Vetter , Helge Deller Cc: Albin Babu Varghese , syzbot+48b0652a95834717f190@syzkaller.appspotmail.com, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH] fbdev: Add bounds checking in bit_putcs to fix vmalloc-out-of-bounds Date: Sat, 27 Sep 2025 03:50:09 -0400 Message-ID: <20250927075010.119671-1-albinbabuvarghese20@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" KASAN reports vmalloc-out-of-bounds writes in sys_imageblit during console resize operations. The crash happens when bit_putcs renders characters=20 outside the allocated framebuffer region. Call trace: vc_do_resize -> clear_selection -> invert_screen -> do_update_region -> fbcon_putcs -> bit_putcs -> sys_imageblit The console resize changes dimensions but bit_putcs doesn't validate that=20 the character positions fit within the framebuffer before rendering.=20 This causes writes past the allocated buffer in fb_imageblit functions. Fix by checking bounds before rendering: - Return if dy + height > yres (would write past bottom) - Break if dx + width > xres (would write past right edge) Reported-by: syzbot+48b0652a95834717f190@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=3D48b0652a95834717f190 =20 Tested-by: syzbot+48b0652a95834717f190@syzkaller.appspotmail.com Signed-off-by: Albin Babu Varghese --- drivers/video/fbdev/core/bitblit.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/= bitblit.c index f9475c14f733..4c732284384a 100644 --- a/drivers/video/fbdev/core/bitblit.c +++ b/drivers/video/fbdev/core/bitblit.c @@ -160,6 +160,9 @@ static void bit_putcs(struct vc_data *vc, struct fb_inf= o *info, image.height =3D vc->vc_font.height; image.depth =3D 1; =20 + if (image.dy + image.height > info->var.yres) + return; + if (attribute) { buf =3D kmalloc(cellsize, GFP_ATOMIC); if (!buf) @@ -173,6 +176,10 @@ static void bit_putcs(struct vc_data *vc, struct fb_in= fo *info, cnt =3D count; =20 image.width =3D vc->vc_font.width * cnt; + + if (image.dx + image.width > info->var.xres) + break; + pitch =3D DIV_ROUND_UP(image.width, 8) + scan_align; pitch &=3D ~scan_align; size =3D pitch * image.height + buf_align; --=20 2.51.0