From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1476DC433B4 for ; Fri, 14 May 2021 16:19:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E7A4E61444 for ; Fri, 14 May 2021 16:19:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233541AbhENQVE (ORCPT ); Fri, 14 May 2021 12:21:04 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:61685 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233385AbhENQVC (ORCPT ); Fri, 14 May 2021 12:21:02 -0400 Received: from fsav107.sakura.ne.jp (fsav107.sakura.ne.jp [27.133.134.234]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id 14EGJn6k024946; Sat, 15 May 2021 01:19:49 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav107.sakura.ne.jp (F-Secure/fsigk_smtp/550/fsav107.sakura.ne.jp); Sat, 15 May 2021 01:19:49 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/550/fsav107.sakura.ne.jp) Received: from [192.168.1.9] (M106072142033.v4.enabler.ne.jp [106.72.142.33]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id 14EGJmMu024941 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NO); Sat, 15 May 2021 01:19:48 +0900 (JST) (envelope-from penguin-kernel@i-love.sakura.ne.jp) Subject: [PATCH] video: fbdev: vga16fb: fix OOB write in vga16fb_imageblit() From: Tetsuo Handa To: dri-devel@lists.freedesktop.org, linux-fbdev@vger.kernel.org, linux-kernel@vger.kernel.org, "Maciej W. Rozycki" , Daniel Vetter References: <0000000000006bbd0c05c14f1b09@google.com> <6e21483c-06f6-404b-4018-e00ee85c456c@i-love.sakura.ne.jp> <87d928e4-b2b9-ad30-f3f0-1dfb8e4e03ed@i-love.sakura.ne.jp> Cc: Linus Torvalds , syzbot , b.zolnierkie@samsung.com, colin.king@canonical.com, gregkh@linuxfoundation.org, jani.nikula@intel.com, jirislaby@kernel.org, syzkaller-bugs@googlegroups.com, "Antonino A. Daplas" Message-ID: <05acdda8-dc1c-5119-4326-96eed24bea0c@i-love.sakura.ne.jp> Date: Sat, 15 May 2021 01:19:48 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.10.1 MIME-Version: 1.0 In-Reply-To: <87d928e4-b2b9-ad30-f3f0-1dfb8e4e03ed@i-love.sakura.ne.jp> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org syzbot is reporting that a local user with the framebuffer console can crash the kernel [1], for ioctl(VT_RESIZE) allows a TTY to set arbitrary rows/columns values regardless of amount of memory reserved for the graphical screen. ---------- #include #include #include #include #include #include int main(int argc, char *argv[]) { const int fd = open("/dev/char/4:1", O_RDWR); struct vt_sizes vt = { 0x4100, 2 }; ioctl(fd, KDSETMODE, KD_GRAPHICS); ioctl(fd, VT_RESIZE, &vt); ioctl(fd, KDSETMODE, KD_TEXT); return 0; } ---------- Currently it is impossible to control upper limit of rows/columns values based on amount of memory reserved for the graphical screen, for resize_screen() calls vc->vc_sw->con_resize() only if vc->vc_mode is not already KD_GRAPHICS. I don't know the reason, and this condition predates the git history. Even if it turns out to be safe to always call this callback, we will need to involve another callback via "struct fb_ops" for checking the upper limits from fbcon_resize(). As a result, we will need to modify drivers/tty/vt/vt.c drivers/video/fbdev/core/fbcon.c drivers/video/fbdev/vga16fb.c include/linux/fb.h files only for checking rows/columns values passed to ioctl(VT_RESIZE) request. Therefore, instead of introducing such a complicated callback chain, avoid this problem by simply checking whether the address to read or write is in [VGA_FB_PHYS, VGA_FB_PHYS + VGA_FB_PHYS_LEN) range. [1] https://syzkaller.appspot.com/bug?extid=1f29e126cf461c4de3b3 Reported-by: syzbot Signed-off-by: Tetsuo Handa Tested-by: syzbot --- drivers/video/fbdev/vga16fb.c | 54 +++++++++++++++++++++++------------ 1 file changed, 36 insertions(+), 18 deletions(-) diff --git a/drivers/video/fbdev/vga16fb.c b/drivers/video/fbdev/vga16fb.c index e2757ff1c23d..13732a3b1d69 100644 --- a/drivers/video/fbdev/vga16fb.c +++ b/drivers/video/fbdev/vga16fb.c @@ -98,6 +98,18 @@ static const struct fb_fix_screeninfo vga16fb_fix = { .accel = FB_ACCEL_NONE }; +/* + * Verify that the address to read or write is in [VGA_FB_PHYS, VGA_FB_PHYS + VGA_FB_PHYS_LEN) + * range, for ioctl(VT_RESIZE) allows a TTY to set arbitrary rows/columns values which will crash + * the kernel due to out of bounds access when trying to redraw the screen. + */ +static inline bool is_valid_iomem(const struct fb_info *info, const char __iomem *where) +{ + return info->screen_base <= where && where < info->screen_base + VGA_FB_PHYS_LEN; +} + +#define IS_SAFE(where) is_valid_iomem(info, (where)) + /* The VGA's weird architecture often requires that we read a byte and write a byte to the same location. It doesn't matter *what* byte we write, however. This is because all the action goes on behind @@ -851,7 +863,7 @@ static void vga_8planes_fillrect(struct fb_info *info, const struct fb_fillrect int x; /* we can do memset... */ - for (x = width; x > 0; --x) { + for (x = width; x > 0 && IS_SAFE(where); --x) { writeb(rect->color, where); where++; } @@ -864,7 +876,7 @@ static void vga_8planes_fillrect(struct fb_info *info, const struct fb_fillrect oldop = setop(0x18); oldsr = setsr(0xf); setmask(0x0F); - for (y = 0; y < rect->height; y++) { + for (y = 0; y < rect->height && IS_SAFE(where) && IS_SAFE(where + 1); y++) { rmw(where); rmw(where+1); where += info->fix.line_length; @@ -919,7 +931,7 @@ static void vga16fb_fillrect(struct fb_info *info, const struct fb_fillrect *rec setmask(0xff); while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(dst); x++) { writeb(0, dst); dst++; } @@ -935,7 +947,7 @@ static void vga16fb_fillrect(struct fb_info *info, const struct fb_fillrect *rec setmask(0xff); while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(dst); x++) { rmw(dst); dst++; } @@ -975,7 +987,7 @@ static void vga_8planes_copyarea(struct fb_info *info, const struct fb_copyarea dest = info->screen_base + dx + area->dy * info->fix.line_length; src = info->screen_base + sx + area->sy * info->fix.line_length; while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(src) && IS_SAFE(dest); x++) { readb(src); writeb(0, dest); src++; @@ -991,7 +1003,7 @@ static void vga_8planes_copyarea(struct fb_info *info, const struct fb_copyarea src = info->screen_base + sx + width + (area->sy + height - 1) * info->fix.line_length; while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(src - 1) && IS_SAFE(dest - 1); x++) { --src; --dest; readb(src); @@ -1065,7 +1077,7 @@ static void vga16fb_copyarea(struct fb_info *info, const struct fb_copyarea *are dst = info->screen_base + (dx/8) + dy * info->fix.line_length; src = info->screen_base + (sx/8) + sy * info->fix.line_length; while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(src) && IS_SAFE(dst); x++) { readb(src); writeb(0, dst); dst++; @@ -1080,7 +1092,7 @@ static void vga16fb_copyarea(struct fb_info *info, const struct fb_copyarea *are src = info->screen_base + (sx/8) + width + (sy + height - 1) * info->fix.line_length; while (height--) { - for (x = 0; x < width; x++) { + for (x = 0; x < width && IS_SAFE(src - 1) && IS_SAFE(dst - 1); x++) { dst--; src--; readb(src); @@ -1130,13 +1142,15 @@ static void vga_8planes_imageblit(struct fb_info *info, const struct fb_image *i where = info->screen_base + dx + image->dy * info->fix.line_length; setmask(0xff); - writeb(image->bg_color, where); - readb(where); + if (IS_SAFE(where)) { + writeb(image->bg_color, where); + readb(where); + } selectmask(); setmask(image->fg_color ^ image->bg_color); setmode(0x42); setop(0x18); - for (y = 0; y < image->height; y++, where += info->fix.line_length) + for (y = 0; y < image->height && IS_SAFE(where); y++, where += info->fix.line_length) writew(transl_h[cdat[y]&0xF] | transl_l[cdat[y] >> 4], where); setmask(oldmask); setsr(oldsr); @@ -1165,14 +1179,16 @@ static void vga_imageblit_expand(struct fb_info *info, const struct fb_image *im selectmask(); setmask(0xff); - writeb(image->bg_color, where); - rmb(); - readb(where); /* fill latches */ + if (IS_SAFE(where)) { + writeb(image->bg_color, where); + rmb(); + readb(where); /* fill latches */ + } setmode(3); wmb(); for (y = 0; y < image->height; y++) { dst = where; - for (x = image->width/8; x--;) + for (x = image->width/8; x-- && IS_SAFE(dst);) writeb(*cdat++, dst++); where += info->fix.line_length; } @@ -1187,7 +1203,7 @@ static void vga_imageblit_expand(struct fb_info *info, const struct fb_image *im setmask(0xff); for (y = 0; y < image->height; y++) { dst = where; - for (x=image->width/8; x--;){ + for (x = image->width/8 && IS_SAFE(dst); x--;) { rmw(dst); setcolor(image->fg_color); selectmask(); @@ -1237,8 +1253,10 @@ static void vga_imageblit_color(struct fb_info *info, const struct fb_image *ima setcolor(*cdat); selectmask(); setmask(1 << (7 - (x % 8))); - fb_readb(dst); - fb_writeb(0, dst); + if (IS_SAFE(dst)) { + fb_readb(dst); + fb_writeb(0, dst); + } cdat++; } -- 2.18.4