Re: [syzbot] BUG: unable to handle kernel paging request in vga16fb_fillrect
From: Randy Dunlap
Date: Sun Aug 29 2021 - 20:25:07 EST
On 7/13/21 10:16 PM, syzbot wrote:
Hello,
syzbot found the following issue on:
HEAD commit: 3dbdb38e Merge branch 'for-5.14' of git://git.kernel.org/p..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1323c402300000
kernel config: https://syzkaller.appspot.com/x/.config?x=a1fcf15a09815757
dashboard link: https://syzkaller.appspot.com/bug?extid=04168c8063cfdde1db5e
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11f0e772300000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1114b9b0300000
Here are the fields that are set in the C reproducer for this ioctl:
#define FBIOPUT_VSCREENINFO 0x4601
*(uint32_t*)0x20000200 = 0x356; // xres: 854
*(uint32_t*)0x20000204 = 8; // yres
*(uint32_t*)0x20000208 = 0x600; // xres_virtual: 1536
*(uint32_t*)0x2000020c = 0x10000000; // yres_virtual: huge
*(uint32_t*)0x20000210 = 0; // xoffset
*(uint32_t*)0x20000214 = 0; // yoffset
*(uint32_t*)0x20000218 = 4; // bits_per_pixel
*(uint32_t*)0x2000021c = 0; // grayscale: false
*(uint32_t*)0x20000220 = 0x3000000; // red bitfield
*(uint32_t*)0x20000224 = 0; // green bitfield
*(uint32_t*)0x20000228 = 0; // blue bitfield
*(uint32_t*)0x2000022c = 0; // transp
*(uint32_t*)0x20000230 = 0; // nonstd: false
*(uint32_t*)0x20000234 = 0; // activate
*(uint32_t*)0x20000238 = 0; // height
*(uint32_t*)0x2000023c = 0; // width
*(uint32_t*)0x20000240 = 0; // accel_flags
*(uint32_t*)0x20000244 = 0; // pixclock
*(uint32_t*)0x20000248 = 0; // left_margin
*(uint32_t*)0x2000024c = 0; // right_margin
*(uint32_t*)0x20000250 = 0; // upper_margin
*(uint32_t*)0x20000254 = 0; // lower_margin
*(uint32_t*)0x20000258 = 0; // hsync_len
*(uint32_t*)0x2000025c = 0; // vsync_len
*(uint32_t*)0x20000260 = 0; // sync
*(uint32_t*)0x20000264 = 0; // vmode
*(uint32_t*)0x20000268 = 0; // rotate
*(uint32_t*)0x2000026c = 0; // colorspace
*(uint32_t*)0x20000270 = 0; // rsvd0
*(uint32_t*)0x20000274 = 0; // rsvd1
*(uint32_t*)0x20000278 = 0; // rsvd2
*(uint32_t*)0x2000027c = 0; // rsvd3
*(uint32_t*)0x20000280 = 0; // notdef...
*(uint32_t*)0x20000284 = 0;
*(uint32_t*)0x20000288 = 0;
*(uint32_t*)0x2000028c = 0;
memset((void*)0x20000290, 0, 16);
syscall(__NR_ioctl, r[0], 0x4601, 0x20000200ul);
Note that yres_virtual is set to 0x10000000. Is there no practical limit
(hence limit check) that can be used here?
Also, in vga16fb_check_var(), beginning at line 404:
404 if (yres > vyres)
405 vyres = yres;
406 if (vxres * vyres > maxmem) {
407 vyres = maxmem / vxres;
408 if (vyres < yres)
409 return -ENOMEM;
410 }
At line 406, the product of vxres * vyres overflows 32 bits (is 0 in this
case/example), so any protection from this block is lost.
But even if yres_virtual (aka vyres) is "only" 0x01000000, so no
multiplication overflow occurs, the resulting value of vyres "seems"
to still be too large and can cause an error [I'm not sure about this
last part -- I need to use a new gcc so that KASAN will work.]
Bisection is inconclusive: the issue happens on the oldest tested release.
bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=10fa45d8300000
final oops: https://syzkaller.appspot.com/x/report.txt?x=12fa45d8300000
console output: https://syzkaller.appspot.com/x/log.txt?x=14fa45d8300000
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+04168c8063cfdde1db5e@xxxxxxxxxxxxxxxxxxxxxxxxx
BUG: unable to handle page fault for address: ffff888001000050
#PF: supervisor write access in kernel mode
#PF: error_code(0x0003) - permissions violation
PGD 10e01067 P4D 10e01067 PUD 10e02067 PMD 80000000010001e1
Oops: 0003 [#1] PREEMPT SMP KASAN
CPU: 1 PID: 8433 Comm: syz-executor067 Tainted: G W 5.13.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline]
RIP: 0010:vga16fb_fillrect+0x993/0x18d0 drivers/video/fbdev/vga16fb.c:923
Code: 6c fd 48 63 44 24 10 45 31 f6 48 89 04 24 e8 44 a6 6c fd 31 ff 89 de 31 ed e8 79 ad 6c fd 85 db 4d 89 ec 74 22 e8 2d a6 6c fd <45> 88 34 24 83 c5 01 89 df 49 83 c4 01 89 ee e8 49 ae 6c fd 39 eb
RSP: 0018:ffffc90000eff848 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 000000000000001b RCX: 0000000000000000
RDX: ffff88802d949c40 RSI: ffffffff8408e403 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8408dd8d
R10: ffffffff8408e3f7 R11: 0000000000000000 R12: ffff888001000050
R13: ffff888001000050 R14: 0000000000000000 R15: 000000000ffeb7ff
FS: 0000000001aa2300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff888001000050 CR3: 00000000346fb000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
bit_clear_margins+0x3f6/0x4b0 drivers/video/fbdev/core/bitblit.c:224
fbcon_clear_margins+0x1f1/0x280 drivers/video/fbdev/core/fbcon.c:1315
fbcon_switch+0xa8c/0x1620 drivers/video/fbdev/core/fbcon.c:2146
redraw_screen+0x2b9/0x740 drivers/tty/vt/vt.c:1021
fbcon_modechanged+0x593/0x6d0 drivers/video/fbdev/core/fbcon.c:2651
fbcon_update_vcs+0x3a/0x50 drivers/video/fbdev/core/fbcon.c:2696
do_fb_ioctl+0x62e/0x690 drivers/video/fbdev/core/fbmem.c:1110
fb_ioctl+0xe7/0x150 drivers/video/fbdev/core/fbmem.c:1185
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:1069 [inline]
__se_sys_ioctl fs/ioctl.c:1055 [inline]
__x64_sys_ioctl+0x193/0x200 fs/ioctl.c:1055
do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x43efd9
Code: 28 c3 e8 2a 14 00 00 66 2e 0f 1f 84 00 00 00 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 c7 c1 c0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc362df848 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043efd9
RDX: 0000000020000200 RSI: 0000000000004601 RDI: 0000000000000003
RBP: 0000000000402fc0 R08: 0000000000000000 R09: 0000000000400488
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000403050
R13: 0000000000000000 R14: 00000000004ac018 R15: 0000000000400488
Modules linked in:
CR2: ffff888001000050
---[ end trace 39dce64bc5621bd3 ]---
RIP: 0010:writeb arch/x86/include/asm/io.h:65 [inline]
RIP: 0010:vga16fb_fillrect+0x993/0x18d0 drivers/video/fbdev/vga16fb.c:923
Code: 6c fd 48 63 44 24 10 45 31 f6 48 89 04 24 e8 44 a6 6c fd 31 ff 89 de 31 ed e8 79 ad 6c fd 85 db 4d 89 ec 74 22 e8 2d a6 6c fd <45> 88 34 24 83 c5 01 89 df 49 83 c4 01 89 ee e8 49 ae 6c fd 39 eb
RSP: 0018:ffffc90000eff848 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 000000000000001b RCX: 0000000000000000
RDX: ffff88802d949c40 RSI: ffffffff8408e403 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000000 R09: ffffffff8408dd8d
R10: ffffffff8408e3f7 R11: 0000000000000000 R12: ffff888001000050
R13: ffff888001000050 R14: 0000000000000000 R15: 000000000ffeb7ff
FS: 0000000001aa2300(0000) GS:ffff8880b9d00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff888001000050 CR3: 00000000346fb000 CR4: 00000000001506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
--
~Randy