On 2021/08/30 17:16, Daniel Vetter wrote:
On Mon, Aug 30, 2021 at 11:30:23AM +0800, tcs.kernel@gmail.com wrote:
From: Haimin Zhang tcs_kernel@tencent.com
yres and vyres can be controlled by user mode parameters, and cause p->vrows to become a negative value. While this value be passed to real_y function, the ypos will be out of screen range.This is an out-of-bounds write bug. some driver will check xres and yres in fb_check_var callback,but some not so we add a common check after that callback.
Signed-off-by: Haimin Zhang tcs_kernel@tencent.com Signed-off-by: Tetsuo Handa penguin-kernel@i-love.sakura.ne.jp
Please s/Signed-off-by: Tetsuo Handa/Suggested-by: Tetsuo Handa/ . It is Haimin who debugged this problem and wrote this patch.
Does this fix a syzbot crash or how was this discovered?
Yes, Haimin's team is running syzkaller locally and found this bug. Therefore, no Reported-by: syzbot tag for this patch.
-------- Forwarded Message -------- Subject: Re: [PATCH v2] fbcon: fix Out-Of-Bounds write in sys_imageblit Message-ID: 33fc0e30-b94c-939f-a708-4b939af43100@gmail.com Date: Mon, 2 Aug 2021 14:50:24 +0800
hi, Tetsuo Handa
i made a test with your suggested code, it can block the out-of-bound bug.
where to add this check logic, i suggest to add it after the driver's fb_check_var callback.because what we plan to add is a common check by framework,but some driver can fault-tolerant invalid parameters(like yres_virtual > yres)
/* exist common check */ if (var->xres < 8 || var->yres < 8) return -EINVAL;
/* callback to drivers, some driver can fix invalid virtual xres or virtual yres */ ret = info->fbops->fb_check_var(var, info); if (ret) return ret; /* we add a more check here, if some drivers can't fix invalid x,y virtual values, we return a -EINVAL */ if (var->yres_virtual < var->yres || var->xres_virtual < var->xres) return -EINVAL;
how about this fix ? i can make a v3 patch.
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c index 1c85514..9fb7e94 100644 --- a/drivers/video/fbdev/core/fbmem.c +++ b/drivers/video/fbdev/core/fbmem.c @@ -1012,6 +1012,10 @@ static int fb_check_caps(struct fb_info *info, struct fb_var_screeninfo *var,
if (ret) return ret; + + /* Virtual resolution cannot be smaller than visible resolution. */ + if (var->yres_virtual < var->yres || var->xres_virtual < var->xres) + return -EINVAL;
if ((var->activate & FB_ACTIVATE_MASK) != FB_ACTIVATE_NOW) return 0;
-------- Forwarded Message -------- Subject: Re: [PATCH]fbcon:fix Out-Of-Bounds write in sys_imageblit Message-ID: a0a228b4-d2e2-4d0d-9bfa-074049f4066b@gmail.com Date: Wed, 28 Jul 2021 11:10:52 +0800
this is my debug log:
1. environment linux kernel: git checkout a4c30b8691f26c6115db6e11ec837c1fb6073953 qemu version:QEMU emulator version 6.0.90 (v6.1.0-rc0-99-g76bf66b913) qemu-system-x86_64 -smp 4 -kernel linux_allyes/build/arch/x86/boot/bzImage -m 4G \ -hda /data/h_image/linux_debug/buster1.img -serial stdio \ -append "earlyprintk=serial console=ttyS0 root=/dev/sda nokaslr" \ -enable-kvm -cpu host -display none -net nic -net user,hostfwd=tcp::1236-:22 -s -S
1.kasan report: ================================================================== BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x12f4/0x1430 Write of size 4 at addr ffffc9000b8c1fe0 by task syz-executor.7/29927
CPU: 0 PID: 29927 Comm: syz-executor.7 Tainted: G E 5.13.0-rc5+ #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014 Call Trace: dump_stack+0x141/0x1d7 print_address_description.constprop.0.cold+0x5/0x2f8 kasan_report.cold+0x7c/0xd8 sys_imageblit+0x12f4/0x1430 drm_fbdev_fb_imageblit+0x15c/0x350 soft_cursor+0x514/0xa30 bit_cursor+0xd07/0x1740 fbcon_cursor+0x51d/0x630 hide_cursor+0x85/0x280 putconsxy+0x1d/0x450 vcs_write+0x9cf/0xb90 vfs_write+0x28e/0xa30 ksys_write+0x12d/0x250 do_syscall_64+0x3a/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae RIP: 0033:0x7f6c6d34cf59 Code: 00 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 07 6f 0c 00 f7 d8 64 89 01 48 RSP: 002b:00007f6c6a832d98 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 RAX: ffffffffffffffda RBX: 000000000069c038 RCX: 00007f6c6d34cf59 RDX: 000000000000008d RSI: 0000000020000040 RDI: 0000000000000003 RBP: 000000000069c038 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 000000000069c044 R13: 00007ffd72091c8f R14: 000000000069c038 R15: 0000000000000001
Memory state around the buggy address: ffffc9000b8c1e80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc9000b8c1f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
ffffc9000b8c1f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
^ ffffc9000b8c2000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc9000b8c2080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ==================================================================
in void sys_imageblit(struct fb_info *p, const struct fb_image *image) { u32 fgcolor, bgcolor, start_index, bitstart, pitch_index = 0; u32 bpl = sizeof(u32), bpp = p->var.bits_per_pixel; u32 width = image->width; u32 dx = image->dx, dy = image->dy; void *dst1;
if (p->state != FBINFO_STATE_RUNNING) return;
bitstart = (dy * p->fix.line_length * 8) + (dx * bpp); start_index = bitstart & (32 - 1); pitch_index = (p->fix.line_length & (bpl - 1)) * 8;
bitstart /= 8; bitstart &= ~(bpl - 1); dst1 = (void __force *)p->screen_base + bitstart; // here is the bug ... } p->screen_base is alloced by drm_fb_helper_generic_probe and size is 0x3000000 (gdb) bt #0 drm_fb_helper_generic_probe (fb_helper=0xffff888105b17800, sizes=<optimized out>) at ../drivers/gpu/drm/drm_fb_helper.c:2342 #1 0xffffffff843f9c6f in drm_fb_helper_single_fb_probe (preferred_bpp=32, fb_helper=0xffff888105b17800) at ../drivers/gpu/drm/drm_fb_helper.c:1668 #2 __drm_fb_helper_initial_config_and_unlock (fb_helper=fb_helper@entry=0xffff888105b17800, bpp_sel=bpp_sel@entry=32) at ../drivers/gpu/drm/drm_fb_helper.c:1826 #3 0xffffffff843fea05 in drm_fb_helper_initial_config (bpp_sel=<optimized out>, fb_helper=0xffff888105b17800) at ../drivers/gpu/drm/drm_fb_helper.c:1921 #4 drm_fb_helper_initial_config (bpp_sel=<optimized out>, fb_helper=0xffff888105b17800) at ../drivers/gpu/drm/drm_fb_helper.c:1913 #5 drm_fbdev_client_hotplug (client=client@entry=0xffff888105b17800) at ../drivers/gpu/drm/drm_fb_helper.c:2423 #6 0xffffffff84402504 in drm_fbdev_generic_setup (dev=dev@entry=0xffff888014632000, preferred_bpp=<optimized out>, preferred_bpp@entry=32) at ../drivers/gpu/drm/drm_fb_helper.c:2510 #7 0xffffffff84587e71 in bochs_pci_probe (ent=<optimized out>, pdev=<optimized out>) at ../drivers/gpu/drm/bochs/bochs_drv.c:134 #8 bochs_pci_probe (pdev=<optimized out>, ent=<optimized out>) at ../drivers/gpu/drm/bochs/bochs_drv.c:99 #9 0xffffffff83f7f3d6 in local_pci_probe (_ddi=_ddi@entry=0xffffc90000647b98) at ../drivers/pci/pci-driver.c:309 #10 0xffffffff83f842e6 in pci_call_probe (id=<optimized out>, dev=0xffff888015a50000, drv=<optimized out>) at ../drivers/pci/pci-driver.c:366 #11 __pci_device_probe (pci_dev=0xffff888015a50000, drv=<optimized out>) at ../drivers/pci/pci-driver.c:391 #12 pci_device_probe (dev=0xffff888015a500c8) at ../drivers/pci/pci-driver.c:434 #13 0xffffffff845d5b50 in really_probe (dev=dev@entry=0xffff888015a500c8, drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>) at ../drivers/base/dd.c:576 #14 0xffffffff845d686d in driver_probe_device (drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>, dev=dev@entry=0xffff888015a500c8) at ../drivers/base/dd.c:763 #15 0xffffffff845d7397 in device_driver_attach (drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>, dev=dev@entry=0xffff888015a500c8) at ../drivers/base/dd.c:1039 #16 0xffffffff845d7556 in __driver_attach (dev=0xffff888015a500c8, data=0xffffffff8c21a930 <bochs_pci_driver+112>) at ../drivers/base/dd.c:1117 #17 0xffffffff845cf008 in bus_for_each_dev (bus=<optimized out>, start=start@entry=0x0 <fixed_percpu_data>, data=data@entry=0xffffffff8c21a930 <bochs_pci_driver+112>, fn=fn@entry=0xffffffff845d73d0 <__driver_attach>) at ../drivers/base/bus.c:305 #18 0xffffffff845d477a in driver_attach (drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>) at ../drivers/base/dd.c:1133 #19 0xffffffff845d3203 in bus_add_driver (drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>) at ../drivers/base/bus.c:622 #20 0xffffffff845d95db in driver_register (drv=drv@entry=0xffffffff8c21a930 <bochs_pci_driver+112>) at ../drivers/base/driver.c:171 #21 0xffffffff83f7dcba in __pci_register_driver (drv=drv@entry=0xffffffff8c21a8c0 <bochs_pci_driver>, owner=owner@entry=0x0 <fixed_percpu_data>, mod_name=mod_name@entry=0xffffffff89d9c4c0 "bochs_drm") at ../drivers/pci/pci-driver.c:1393 #22 0xffffffff8e85e6cb in bochs_init () at ../drivers/gpu/drm/bochs/bochs_drv.c:191 #23 0xffffffff81002285 in do_one_initcall (fn=0xffffffff8e85e65d <bochs_init>) at ../init/main.c:1249 #24 0xffffffff8e7ab5f8 in do_initcall_level (command_line=0xffff888135a06c00 "earlyprintk", level=<optimized out>) at ../include/linux/compiler.h:234 #25 do_initcalls () at ../init/main.c:1338 #26 do_basic_setup () at ../init/main.c:1358 #27 kernel_init_freeable () at ../init/main.c:1560 #28 0xffffffff8915d45b in kernel_init (unused=<optimized out>) at ../init/main.c:1447 #29 0xffffffff810046ff in ret_from_fork () at ../arch/x86/entry/entry_64.S:294 #30 0x0000000000000000 in ?? () (gdb) l 2337 2338 drm_fb_helper_fill_info(fbi, fb_helper, sizes); 2339 2340 if (drm_fbdev_use_shadow_fb(fb_helper)) { 2341 fbi->screen_buffer = vzalloc(fbi->screen_size); 2342 if (!fbi->screen_buffer) 2343 return -ENOMEM; 2344 2345 fbi->fbdefio = &drm_fbdev_defio; 2346 (gdb) p/x fbi->screen_size $1 = 0x300000 (gdb) p/x fbi->screen_buffer $2 = 0xffffc9000c561000 (gdb) p/x fbi->screen_base $3 = 0xffffc9000c561000
when run the poc :
Thread 1 hit Breakpoint 2, updatescrollmode (info=info@entry=0xffff8881081bd000, vc=vc@entry=0xffff888010479000, p=<optimized out>) at ../drivers/video/fbdev/core/fbcon.c:1950 1950 static void updatescrollmode(struct fbcon_display *p, (gdb) frame 1 #1 0xffffffff8401d9c3 in fbcon_resize (vc=vc@entry=0xffff888010479000, width=width@entry=20, height=height@entry=7, user=user@entry=0) at ../drivers/video/fbdev/core/fbcon.c:2030 2030 updatescrollmode(p, info, vc); (gdb) p p->vrows $5 = 48 (gdb) p &p->vrows $6 = (int *) 0xffffffff90056094 <fb_display+20> (gdb) frame 0 #0 updatescrollmode (info=info@entry=0xffff8881081bd000, vc=vc@entry=0xffff888010479000, p=<optimized out>) at ../drivers/video/fbdev/core/fbcon.c:1950 1950 static void updatescrollmode(struct fbcon_display *p, (gdb) n 1954 struct fbcon_ops *ops = info->fbcon_par; (gdb) 1955 int fh = vc->vc_font.height; (gdb) 1956 int yres = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres); (gdb) 1957 int vyres = FBCON_SWAP(ops->rotate, info->var.yres_virtual, (gdb) 1960 p->vrows = vyres/fh; (gdb) 1961 if (yres > (fh * (vc->vc_rows + 1))) (gdb) p info.var.yres_virtual $8 = 0 (gdb) p info.var.xres_virtual $9 = 0 (gdb) p info.var.xres $10 = 160 (gdb) p info.var.yres $11 = 120 (gdb) p yres $12 = 120 (gdb) n 1963 if ((yres % fh) && (vyres % fh < yres % fh)) (gdb) n 1964 p->vrows--;
(gdb) x/1wd 0xffffffff90056094 0xffffffff90056094 <fb_display+20>: -1 (gdb) p vc->vc_font $19 = {width = 8, height = 16, charcount = 256, data = 0xffffffff89c532d0 <fontdata_8x16+16> ""}
the kasan backtrace debug in gdb
Thread 2 hit Breakpoint 6, sys_imageblit (p=p@entry=0xffff8881081bd000, image=image@entry=0xffff888011f85080) at ../drivers/video/fbdev/core/sysimgblt.c:244 244 u32 width = image->width; (gdb) n 248 if (p->state != FBINFO_STATE_RUNNING) (gdb) 251 bitstart = (dy * p->fix.line_length * 8) + (dx * bpp); (gdb) 252 start_index = bitstart & (32 - 1); (gdb) 253 pitch_index = (p->fix.line_length & (bpl - 1)) * 8; (gdb) 257 dst1 = (void __force *)p->screen_base + bitstart; (gdb) n 259 if (p->fbops->fb_sync) (gdb) p dst1 $23 = (void *) 0xffffc9000c5a1220 (gdb) p p->screen_base $24 = 0xffffc9000c561000 "" (gdb) p/x 0xffffc9000c5a1220-0xffffc9000c561000 $25 = 0x40220 (gdb) bt #0 sys_imageblit (p=p@entry=0xffff8881081bd000, image=image@entry=0xffff888011f85080) at ../drivers/video/fbdev/core/sysimgblt.c:259 #1 0xffffffff843fbbcc in drm_fb_helper_sys_imageblit (info=info@entry=0xffff8881081bd000, image=image@entry=0xffff888011f85080) at ../drivers/gpu/drm/drm_fb_helper.c:794 #2 0xffffffff843fc831 in drm_fbdev_fb_imageblit (info=0xffff8881081bd000, image=0xffff888011f85080) at ../drivers/gpu/drm/drm_fb_helper.c:2276 #3 0xffffffff8402eff4 in soft_cursor (info=info@entry=0xffff8881081bd000, cursor=cursor@entry=0xffffc9001090f9f0) at ../drivers/video/fbdev/core/softcursor.c:74 #4 0xffffffff8402deb2 in bit_cursor (vc=vc@entry=0xffff888010479000, info=info@entry=0xffff8881081bd000, mode=mode@entry=1, fg=<optimized out>, bg=bg@entry=0) at ../drivers/video/fbdev/core/bitblit.c:377 #5 0xffffffff84019d5e in fbcon_cursor (vc=0xffff888010479000, mode=1) at ../drivers/video/fbdev/core/fbcon.c:1339 #6 0xffffffff842a5155 in set_cursor (vc=0xffff888010479000) at ../drivers/tty/vt/vt.c:920 #7 set_cursor (vc=0xffff888010479000) at ../drivers/tty/vt/vt.c:911 #8 0xffffffff842a6135 in redraw_screen (vc=vc@entry=0xffff888010479000, is_switch=is_switch@entry=0) at ../drivers/tty/vt/vt.c:1037 #9 0xffffffff8401c46c in fbcon_modechanged (info=info@entry=0xffff8881081bd000) at ../drivers/video/fbdev/core/fbcon.c:2651 #10 0xffffffff8401d2da in fbcon_update_vcs (info=info@entry=0xffff8881081bd000, all=all@entry=false) at ../drivers/video/fbdev/core/fbcon.c:2696 #11 0xffffffff83ffa426 in do_fb_ioctl (info=info@entry=0xffff8881081bd000, cmd=cmd@entry=17921, arg=arg@entry=536870912) at ../drivers/video/fbdev/core/fbmem.c:1110 #12 0xffffffff83ffa577 in fb_ioctl (file=file@entry=0xffff88810e274500, cmd=cmd@entry=17921, arg=arg@entry=536870912) at ../drivers/video/fbdev/core/fbmem.c:1185 #13 0xffffffff81cab763 in vfs_ioctl (arg=536870912, cmd=17921, filp=0xffff88810e274500) at ../fs/ioctl.c:51 #14 __do_sys_ioctl (arg=536870912, cmd=17921, fd=3) at ../fs/ioctl.c:1069 #15 __se_sys_ioctl (arg=536870912, cmd=17921, fd=3) at ../fs/ioctl.c:1055 #16 __x64_sys_ioctl (regs=<optimized out>) at ../fs/ioctl.c:1055 #17 0xffffffff89158596 in do_syscall_64 (nr=<optimized out>, regs=0xffffc9001090ff58) at ../arch/x86/entry/common.c:47 #18 0xffffffff89200068 in entry_SYSCALL_64 () at ../arch/x86/entry/entry_64.S:112 #19 0x0000000000000000 in ?? ()
(gdb) frame 0 #0 sys_imageblit (p=p@entry=0xffff8881081bd000, image=image@entry=0xffff888011f85080) at ../drivers/video/fbdev/core/sysimgblt.c:259 259 if (p->fbops->fb_sync) (gdb) p image.dy $29 = 64 (gdb) p image.dx $30 = 136 (gdb) frame 1 #1 0xffffffff843fbbcc in drm_fb_helper_sys_imageblit (info=info@entry=0xffff8881081bd000, image=image@entry=0xffff888011f85080) at ../drivers/gpu/drm/drm_fb_helper.c:794 794 sys_imageblit(info, image); (gdb) p info.screen_ screen_base screen_buffer screen_size (gdb) p info.screen_size $31 = 3145728 (gdb) p/x info.screen_size $32 = 0x300000
(gdb) frame 4 #4 0xffffffff8402deb2 in bit_cursor (vc=vc@entry=0xffff888010479000, info=info@entry=0xffff8881081bd000, mode=mode@entry=1, fg=<optimized out>, bg=bg@entry=0) at ../drivers/video/fbdev/core/bitblit.c:377 377 soft_cursor(info, &cursor); (gdb) p ops->p.vrows $38 = -1 (gdb) p &ops->p.vrows $39 = (int *) 0xffffffff90056094 <fb_display+20>
在 2021/7/27 23:10, Tetsuo Handa 写道:
OK, test.c was generated by syzkaller, and I guess that your team is running syzkaller in your environment.
It seems that test.c is doing
struct fb_var_screeninfo var = { ... }; int fd_fb0 = open("/dev/fb0", O_RDONLY); ioctl(fd_fb0, FBIOPUT_VSCREENINFO, &var);
int fd_vcs = open("/dev/vcsa5", O_WRONLY|O_NOCTTY|O_NONBLOCK); write(fd_vcs, "\16\272P\323\236\3\377\231\34\0\0\0", 12);
in parallel and hitting some race.
I don't have environment to test with KASAN now. But syzbot dashboard indicates that crash in sys_imageblit is not happening recently.
KASAN: vmalloc-out-of-bounds Write in sys_imageblit https://syzkaller.appspot.com/bug?id=d2e785fe8b66425f3a2be0a209b08456f8200b5...
BUG: unable to handle kernel paging request in sys_imageblit https://syzkaller.appspot.com/bug?id=26d6ef43f58d17c6899c63a53544ee9bb26d0bf...
You need to provide more information. Are you seeing this problem with v5.14-rc3 ? Please provide full oops report. Please show a URL for this problem if this problem was reported somewhere.