diff mbox series

fbconsole needs more parameter validations.

Message ID b1e7dd6a-fc22-bba8-0abb-d3e779329bce@i-love.sakura.ne.jp (mailing list archive)
State Superseded, archived
Headers show
Series fbconsole needs more parameter validations. | expand

Commit Message

Tetsuo Handa July 10, 2020, 5:56 a.m. UTC 
Hello.

While trying to debug https://syzkaller.appspot.com/bug?extid=017265e8553724e514e8 ,
I noticed that a crash can happen without opening /dev/ttyXX .

For example, while a driver which syzbot is reporting accepts screen with
var.xres = var.yres = 0 (and a crash is not visible until trying to write to
/dev/ttyXX ), a driver for VMware environment which I'm using (dmesg says "fbcon:
svgadrmfb (fb0) is primary device") rejects screen with var.xres = var.yres = 0.
However, specifying var.xres = var.yres = 1 like below reproducer causes a crash
in my VMware environment.

----------
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/fb.h>

int main(int argc, char *argv[])
{
        const int fd = open("/dev/fb0", O_ACCMODE);
        struct fb_var_screeninfo var = { };
        ioctl(fd, FBIOGET_VSCREENINFO, &var);
        var.xres = var.yres = 1;
        ioctl(fd, FBIOPUT_VSCREENINFO, &var);
        return 0;
}
----------

----------
[   20.102222] BUG: unable to handle page fault for address: ffffb80500d7b000
[   20.102225] #PF: supervisor write access in kernel mode
[   20.102226] #PF: error_code(0x0002) - not-present page
[   20.102227] PGD 13a48c067 P4D 13a48c067 PUD 13a48d067 PMD 132525067 PTE 0
[   20.102230] Oops: 0002 [#1] SMP
[   20.102232] CPU: 3 PID: 2786 Comm: a.out Not tainted 5.8.0-rc4+ #749
[   20.102233] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[   20.102237] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
[   20.102238] Code: c3 45 85 db 0f 85 85 00 00 00 44 89 c0 31 d2 41 f7 f1 89 c2 83 f8 07 76 41 8d 48 f8 c1 e9 03 48 83 c1 01 48 c1 e1 06 48 01 f1 <48> 89 3e 48 89 7e 08 48 89 7e 10 48 89 7e 18 48 89 7e 20 48 89 7e
[   20.102239] RSP: 0018:ffffb805012939a8 EFLAGS: 00010206
[   20.102240] RAX: 0000000003fffe70 RBX: 00000000ffff9c20 RCX: ffffb80520982000
[   20.102241] RDX: 0000000003fffe70 RSI: ffffb80500d7b000 RDI: 0000000000000000
[   20.102242] RBP: ffffb805012939b8 R08: 00000000ffff9c20 R09: ffffb80500d7aff8
[   20.102242] R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffffffffffff
[   20.102243] R13: ffff976734c0c000 R14: 0000000000000000 R15: ffffb80500982c80
[   20.102244] FS:  00007f0c9589e740(0000) GS:ffff97673aec0000(0000) knlGS:0000000000000000
[   20.102265] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   20.102265] CR2: ffffb80500d7b000 CR3: 0000000136cdf004 CR4: 00000000001606e0
[   20.102277] Call Trace:
[   20.102281]  cfb_fillrect+0x159/0x340 [cfbfillrect]
[   20.102385]  ? __mutex_unlock_slowpath+0x158/0x2d0
[   20.102493]  ? cfb_fillrect+0x340/0x340 [cfbfillrect]
[   20.102747]  vmw_fb_fillrect+0x12/0x30 [vmwgfx]
[   20.102755]  bit_clear_margins+0x92/0xf0 [fb]
[   20.102760]  fbcon_clear_margins+0x4c/0x50 [fb]
[   20.102763]  fbcon_switch+0x321/0x570 [fb]
[   20.102771]  redraw_screen+0xe0/0x250
[   20.102775]  fbcon_modechanged+0x164/0x1b0 [fb]
[   20.102779]  fbcon_update_vcs+0x15/0x20 [fb]
[   20.102781]  fb_set_var+0x364/0x3c0 [fb]
[   20.102817]  do_fb_ioctl+0x2ff/0x3f0 [fb]
[   20.102894]  ? find_held_lock+0x35/0xa0
[   20.103126]  ? __audit_syscall_entry+0xd8/0x120
[   20.103135]  ? kfree+0x25a/0x2b0
[   20.103139]  fb_ioctl+0x2e/0x40 [fb]
[   20.103141]  ksys_ioctl+0x86/0xc0
[   20.103144]  ? do_syscall_64+0x20/0xa0
[   20.103146]  __x64_sys_ioctl+0x15/0x20
[   20.103148]  do_syscall_64+0x54/0xa0
[   20.103151]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   20.103152] RIP: 0033:0x7f0c953b8307
[   20.103153] Code: Bad RIP value.
[   20.103154] RSP: 002b:00007ffecbdce0f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   20.103155] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f0c953b8307
[   20.103156] RDX: 00007ffecbdce100 RSI: 0000000000004601 RDI: 0000000000000003
[   20.103156] RBP: 0000000000000000 R08: 00007f0c9568be80 R09: 0000000000000000
[   20.103157] R10: 00007ffecbdcdb60 R11: 0000000000000246 R12: 00000000004004f2
[   20.103158] R13: 00007ffecbdce280 R14: 0000000000000000 R15: 0000000000000000
[   20.103162] Modules linked in: mousedev rapl evdev input_leds led_class mac_hid psmouse pcspkr xt_tcpudp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack sg ebtable_nat af_packet ip6table_nat ip6table_mangle ip6table_raw iptable_nat nf_nat iptable_mangle iptable_raw nf_conntrack rtc_cmos nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter bpfilter i2c_piix4 vmw_vmci ac intel_agp button intel_gtt ip_tables x_tables ata_generic pata_acpi serio_raw atkbd libps2 vmwgfx drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea fb fbdev ttm drm i2c_core ahci drm_panel_orientation_quirks libahci backlight e1000 agpgart ata_piix libata i8042 serio unix ipv6 nf_defrag_ipv6
[   20.103194] CR2: ffffb80500d7b000
[   20.103196] ---[ end trace b2348f839f6524f9 ]---
[   20.103198] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
[   20.103200] Code: c3 45 85 db 0f 85 85 00 00 00 44 89 c0 31 d2 41 f7 f1 89 c2 83 f8 07 76 41 8d 48 f8 c1 e9 03 48 83 c1 01 48 c1 e1 06 48 01 f1 <48> 89 3e 48 89 7e 08 48 89 7e 10 48 89 7e 18 48 89 7e 20 48 89 7e
[   20.103201] RSP: 0018:ffffb805012939a8 EFLAGS: 00010206
[   20.103202] RAX: 0000000003fffe70 RBX: 00000000ffff9c20 RCX: ffffb80520982000
[   20.103202] RDX: 0000000003fffe70 RSI: ffffb80500d7b000 RDI: 0000000000000000
[   20.103203] RBP: ffffb805012939b8 R08: 00000000ffff9c20 R09: ffffb80500d7aff8
[   20.103204] R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffffffffffff
[   20.103204] R13: ffff976734c0c000 R14: 0000000000000000 R15: ffffb80500982c80
[   20.103205] FS:  00007f0c9589e740(0000) GS:ffff97673aec0000(0000) knlGS:0000000000000000
[   20.103213] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   20.103214] CR2: ffffb80500d7b000 CR3: 0000000136cdf004 CR4: 00000000001606e0
----------

A debug printk() patch

----------
----------

says that width * bpp was a sane value for normal boot

  [    9.993434] height=16 width=800 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=21676032 p->fix.line_length=4704
  [   15.494941] height=8 width=800 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=22278144 p->fix.line_length=4704

but width * bpp was overflowing when the reproducer shown above was executed.

  [   28.164111] height=885 width=4294966497 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=25600 p->fix.line_length=4704

syzbot has several bug reports which are stalling inside filling functions. I guess
that these reports are unexpectedly longer loops caused by integer overflow/underflow.

Thus, I consider that we need more sanity/constraints checks.
I don't have other devices to test. Please check your drivers.

Comments

Greg Kroah-Hartman July 10, 2020, 10:56 a.m. UTC | #1 
On Fri, Jul 10, 2020 at 02:56:58PM +0900, Tetsuo Handa wrote:
> Hello.
> 
> While trying to debug https://syzkaller.appspot.com/bug?extid=017265e8553724e514e8 ,
> I noticed that a crash can happen without opening /dev/ttyXX .
> 
> For example, while a driver which syzbot is reporting accepts screen with
> var.xres = var.yres = 0 (and a crash is not visible until trying to write to
> /dev/ttyXX ), a driver for VMware environment which I'm using (dmesg says "fbcon:
> svgadrmfb (fb0) is primary device") rejects screen with var.xres = var.yres = 0.
> However, specifying var.xres = var.yres = 1 like below reproducer causes a crash
> in my VMware environment.
> 
> ----------
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <sys/ioctl.h>
> #include <linux/fb.h>
> 
> int main(int argc, char *argv[])
> {
>         const int fd = open("/dev/fb0", O_ACCMODE);
>         struct fb_var_screeninfo var = { };
>         ioctl(fd, FBIOGET_VSCREENINFO, &var);
>         var.xres = var.yres = 1;
>         ioctl(fd, FBIOPUT_VSCREENINFO, &var);
>         return 0;
> }
> ----------
> 
> ----------
> [   20.102222] BUG: unable to handle page fault for address: ffffb80500d7b000
> [   20.102225] #PF: supervisor write access in kernel mode
> [   20.102226] #PF: error_code(0x0002) - not-present page
> [   20.102227] PGD 13a48c067 P4D 13a48c067 PUD 13a48d067 PMD 132525067 PTE 0
> [   20.102230] Oops: 0002 [#1] SMP
> [   20.102232] CPU: 3 PID: 2786 Comm: a.out Not tainted 5.8.0-rc4+ #749
> [   20.102233] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
> [   20.102237] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
> [   20.102238] Code: c3 45 85 db 0f 85 85 00 00 00 44 89 c0 31 d2 41 f7 f1 89 c2 83 f8 07 76 41 8d 48 f8 c1 e9 03 48 83 c1 01 48 c1 e1 06 48 01 f1 <48> 89 3e 48 89 7e 08 48 89 7e 10 48 89 7e 18 48 89 7e 20 48 89 7e
> [   20.102239] RSP: 0018:ffffb805012939a8 EFLAGS: 00010206
> [   20.102240] RAX: 0000000003fffe70 RBX: 00000000ffff9c20 RCX: ffffb80520982000
> [   20.102241] RDX: 0000000003fffe70 RSI: ffffb80500d7b000 RDI: 0000000000000000
> [   20.102242] RBP: ffffb805012939b8 R08: 00000000ffff9c20 R09: ffffb80500d7aff8
> [   20.102242] R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffffffffffff
> [   20.102243] R13: ffff976734c0c000 R14: 0000000000000000 R15: ffffb80500982c80
> [   20.102244] FS:  00007f0c9589e740(0000) GS:ffff97673aec0000(0000) knlGS:0000000000000000
> [   20.102265] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   20.102265] CR2: ffffb80500d7b000 CR3: 0000000136cdf004 CR4: 00000000001606e0
> [   20.102277] Call Trace:
> [   20.102281]  cfb_fillrect+0x159/0x340 [cfbfillrect]
> [   20.102385]  ? __mutex_unlock_slowpath+0x158/0x2d0
> [   20.102493]  ? cfb_fillrect+0x340/0x340 [cfbfillrect]
> [   20.102747]  vmw_fb_fillrect+0x12/0x30 [vmwgfx]
> [   20.102755]  bit_clear_margins+0x92/0xf0 [fb]
> [   20.102760]  fbcon_clear_margins+0x4c/0x50 [fb]
> [   20.102763]  fbcon_switch+0x321/0x570 [fb]
> [   20.102771]  redraw_screen+0xe0/0x250
> [   20.102775]  fbcon_modechanged+0x164/0x1b0 [fb]
> [   20.102779]  fbcon_update_vcs+0x15/0x20 [fb]
> [   20.102781]  fb_set_var+0x364/0x3c0 [fb]
> [   20.102817]  do_fb_ioctl+0x2ff/0x3f0 [fb]
> [   20.102894]  ? find_held_lock+0x35/0xa0
> [   20.103126]  ? __audit_syscall_entry+0xd8/0x120
> [   20.103135]  ? kfree+0x25a/0x2b0
> [   20.103139]  fb_ioctl+0x2e/0x40 [fb]
> [   20.103141]  ksys_ioctl+0x86/0xc0
> [   20.103144]  ? do_syscall_64+0x20/0xa0
> [   20.103146]  __x64_sys_ioctl+0x15/0x20
> [   20.103148]  do_syscall_64+0x54/0xa0
> [   20.103151]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [   20.103152] RIP: 0033:0x7f0c953b8307
> [   20.103153] Code: Bad RIP value.
> [   20.103154] RSP: 002b:00007ffecbdce0f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> [   20.103155] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f0c953b8307
> [   20.103156] RDX: 00007ffecbdce100 RSI: 0000000000004601 RDI: 0000000000000003
> [   20.103156] RBP: 0000000000000000 R08: 00007f0c9568be80 R09: 0000000000000000
> [   20.103157] R10: 00007ffecbdcdb60 R11: 0000000000000246 R12: 00000000004004f2
> [   20.103158] R13: 00007ffecbdce280 R14: 0000000000000000 R15: 0000000000000000
> [   20.103162] Modules linked in: mousedev rapl evdev input_leds led_class mac_hid psmouse pcspkr xt_tcpudp ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack sg ebtable_nat af_packet ip6table_nat ip6table_mangle ip6table_raw iptable_nat nf_nat iptable_mangle iptable_raw nf_conntrack rtc_cmos nf_defrag_ipv4 ip_set nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter bpfilter i2c_piix4 vmw_vmci ac intel_agp button intel_gtt ip_tables x_tables ata_generic pata_acpi serio_raw atkbd libps2 vmwgfx drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea fb fbdev ttm drm i2c_core ahci drm_panel_orientation_quirks libahci backlight e1000 agpgart ata_piix libata i8042 serio unix ipv6 nf_defrag_ipv6
> [   20.103194] CR2: ffffb80500d7b000
> [   20.103196] ---[ end trace b2348f839f6524f9 ]---
> [   20.103198] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
> [   20.103200] Code: c3 45 85 db 0f 85 85 00 00 00 44 89 c0 31 d2 41 f7 f1 89 c2 83 f8 07 76 41 8d 48 f8 c1 e9 03 48 83 c1 01 48 c1 e1 06 48 01 f1 <48> 89 3e 48 89 7e 08 48 89 7e 10 48 89 7e 18 48 89 7e 20 48 89 7e
> [   20.103201] RSP: 0018:ffffb805012939a8 EFLAGS: 00010206
> [   20.103202] RAX: 0000000003fffe70 RBX: 00000000ffff9c20 RCX: ffffb80520982000
> [   20.103202] RDX: 0000000003fffe70 RSI: ffffb80500d7b000 RDI: 0000000000000000
> [   20.103203] RBP: ffffb805012939b8 R08: 00000000ffff9c20 R09: ffffb80500d7aff8
> [   20.103204] R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffffffffffff
> [   20.103204] R13: ffff976734c0c000 R14: 0000000000000000 R15: ffffb80500982c80
> [   20.103205] FS:  00007f0c9589e740(0000) GS:ffff97673aec0000(0000) knlGS:0000000000000000
> [   20.103213] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [   20.103214] CR2: ffffb80500d7b000 CR3: 0000000136cdf004 CR4: 00000000001606e0
> ----------
> 
> A debug printk() patch
> 
> ----------
> diff --git a/drivers/video/fbdev/core/cfbfillrect.c b/drivers/video/fbdev/core/cfbfillrect.c
> index ba9f58b2a5e8..57e4c2d1bcc0 100644
> --- a/drivers/video/fbdev/core/cfbfillrect.c
> +++ b/drivers/video/fbdev/core/cfbfillrect.c
> @@ -321,6 +321,9 @@ void cfb_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
>  			fill_op32 = bitfill_aligned;
>  			break;
>  		}
> +		if (fill_op32 == bitfill_aligned)
> +			printk(KERN_DEBUG "height=%lu width=%lu bpp=%u bits=%u bytes=%u dst=%px dst_idx=%u p->fix.line_length=%u\n",
> +			       height, width, bpp, bits, bytes, dst, dst_idx, p->fix.line_length);
>  		while (height--) {
>  			dst += dst_idx >> (ffs(bits) - 1);
>  			dst_idx &= (bits - 1);
> ----------
> 
> says that width * bpp was a sane value for normal boot
> 
>   [    9.993434] height=16 width=800 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=21676032 p->fix.line_length=4704
>   [   15.494941] height=8 width=800 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=22278144 p->fix.line_length=4704
> 
> but width * bpp was overflowing when the reproducer shown above was executed.
> 
>   [   28.164111] height=885 width=4294966497 bpp=32 bits=64 bytes=8 dst=ffff9864409c2000 dst_idx=25600 p->fix.line_length=4704
> 
> syzbot has several bug reports which are stalling inside filling functions. I guess
> that these reports are unexpectedly longer loops caused by integer overflow/underflow.
> 
> Thus, I consider that we need more sanity/constraints checks.
> I don't have other devices to test. Please check your drivers.


What drivers?

Where is the over/underflow happening here when we set a size to be so
small?  We should bound the size somewhere, and as you show, that's not
really working properly, right?

thanks,

greg k-h
Tetsuo Handa July 11, 2020, 6:16 a.m. UTC | #2 
On 2020/07/10 19:56, Greg Kroah-Hartman wrote:
> Where is the over/underflow happening here when we set a size to be so
> small?  We should bound the size somewhere, and as you show, that's not
> really working properly, right?

It is bit_clear_margins() where integer underflow is happening (4294966497 == 1 - 100 * 8),
but the cause of this problem seems to be fbcon_startup() or vc_do_resize().

Since fbcon_modechanged() is doing

  cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
  rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
  cols /= vc->vc_font.width;
  rows /= vc->vc_font.height;
  vc_resize(vc, cols, rows);
  (...snipped...)
  update_screen(vc);

, info->var.xres < vc->vc_font.width makes cols == 0 and info->var.yres < vc->vc_font.height
makes rows == 0. But vc_resize(vc, 0, 0) has a special meaning because vc_do_resize() is doing

  new_cols = (cols ? cols : vc->vc_cols);
  new_rows = (lines ? lines : vc->vc_rows);

which results in new_cols == 100 and new_rows == 37 despite var.xres == var.yres == 1,
and vc_do_resize() returns without actually resizing. Then, fbcon_modechanged() calls
fbcon_switch(vc) via vc->vc_sw->con_switch(vc) via redraw_screen(vc, 0) via update_screen(vc),
and fbcon_switch() calls bit_clear_margins() via fbcon_clear_margins(vc, 0), and integer
underflow happens due to info->var.xres=1 && vc->vc_cols=100 && vc->vc_font.width=8.

And fbcon_modechanged() is too late to return -EINVAL if
info->var.xres < vc->vc_font.width || info->var.yres < vc->vc_font.height at fb_set_var().

----------
diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
index 42d8c67a481f..4af82cabb6c4 100644
--- a/drivers/tty/vt/vt.c
+++ b/drivers/tty/vt/vt.c
@@ -1214,6 +1214,8 @@ static int vc_do_resize(struct tty_struct *tty, struct vc_data *vc,
 	new_rows = (lines ? lines : vc->vc_rows);
 	new_row_size = new_cols << 1;
 	new_screen_size = new_row_size * new_rows;
+	printk(KERN_DEBUG "%s: new_cols=%u cols=%u vc->vc_cols=%u new_rows=%u lines=%u vc->vc_rows=%u\n",
+	       __func__, new_cols, cols, vc->vc_cols, new_rows, lines, vc->vc_rows);
 
 	if (new_cols == vc->vc_cols && new_rows == vc->vc_rows)
 		return 0;
diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c
index ca935c09a261..8d949679bfba 100644
--- a/drivers/video/fbdev/core/bitblit.c
+++ b/drivers/video/fbdev/core/bitblit.c
@@ -221,6 +221,8 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
 		region.dy = 0;
 		region.width = rw;
 		region.height = info->var.yres_virtual;
+		printk(KERN_DEBUG "%s: rw=%u info->var.xres=%u vc->vc_cols=%u vc->vc_font.width=%u\n",
+		       __func__, rw, info->var.xres, vc->vc_cols, vc->vc_font.width);
 		info->fbops->fb_fillrect(info, &region);
 	}
 
@@ -229,6 +231,8 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
 		region.dy = info->var.yoffset + bs;
 		region.width = rs;
 		region.height = bh;
+		printk(KERN_DEBUG "%s: bh=%u info->var.yres=%u vc->vc_rows=%u vc->vc_font.height=%u\n",
+		       __func__, bh, info->var.yres, vc->vc_rows, vc->vc_font.height);
 		info->fbops->fb_fillrect(info, &region);
 	}
 }
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index e2a490c5ae08..f83525a58137 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2983,6 +2983,8 @@ static void fbcon_modechanged(struct fb_info *info)
 
 	if (con_is_visible(vc)) {
 		var_to_display(p, &info->var, info);
+		printk(KERN_DEBUG "%s: ops->rotate=%d info->var.xres=%u, info->var.yres=%u vc->vc_font.width=%u vc->vc_font.height=%u\n",
+		       __func__, ops->rotate, info->var.xres, info->var.yres, vc->vc_font.width, vc->vc_font.height);
 		cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
 		rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
 		cols /= vc->vc_font.width;
----------

----------
[   21.854895][ T2790] fbcon_modechanged: ops->rotate=0 info->var.xres=1, info->var.yres=1 vc->vc_font.width=8 vc->vc_font.height=16
[   21.854900][ T2790] vc_do_resize: new_cols=100 cols=0 vc->vc_cols=100 new_rows=37 lines=0 vc->vc_rows=37
[   21.854909][ T2790] bit_clear_margins: rw=4294966497 info->var.xres=1 vc->vc_cols=100 vc->vc_font.width=8
[   21.855743][ T2790] BUG: unable to handle page fault for address: ffffb54440d3b000
[   21.855745][ T2790] #PF: supervisor write access in kernel mode
[   21.855746][ T2790] #PF: error_code(0x0002) - not-present page
[   21.855747][ T2790] PGD 13a48c067 P4D 13a48c067 PUD 13a48d067 PMD 13251c067 PTE 0
[   21.855751][ T2790] Oops: 0002 [#1] SMP
[   21.855753][ T2790] CPU: 0 PID: 2790 Comm: a.out Not tainted 5.8.0-rc4+ #753
[   21.855754][ T2790] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 02/27/2020
[   21.855758][ T2790] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
[   21.855759][ T2790] Code: c3 45 85 db 0f 85 85 00 00 00 44 89 c0 31 d2 41 f7 f1 89 c2 83 f8 07 76 41 8d 48 f8 c1 e9 03 48 83 c1 01 48 c1 e1 06 48 01 f1 <48> 89 3e 48 89 7e 08 48 89 7e 10 48 89 7e 18 48 89 7e 20 48 89 7e
[   21.855760][ T2790] RSP: 0018:ffffb5444124b9a0 EFLAGS: 00010206
[   21.855761][ T2790] RAX: 0000000003fffe70 RBX: 00000000ffff9c20 RCX: ffffb54460942000
[   21.855762][ T2790] RDX: 0000000003fffe70 RSI: ffffb54440d3b000 RDI: 0000000000000000
[   21.855763][ T2790] RBP: ffffb5444124b9b0 R08: 00000000ffff9c20 R09: ffffb54440d3aff8
[   21.855763][ T2790] R10: 00000000ffffffff R11: 0000000000000000 R12: ffffffffffffffff
[   21.855764][ T2790] R13: ffffa0d534c32800 R14: 0000000000000000 R15: ffffb54440942c80
[   21.855765][ T2790] FS:  00007f9cef82a740(0000) GS:ffffa0d53ae00000(0000) knlGS:0000000000000000
[   21.855785][ T2790] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   21.855786][ T2790] CR2: ffffb54440d3b000 CR3: 000000013766d006 CR4: 00000000001606f0
[   21.855797][ T2790] Call Trace:
[   21.855801][ T2790]  cfb_fillrect+0x159/0x340 [cfbfillrect]
[   21.855806][ T2790]  ? vprintk_func+0x5a/0x10d
[   21.855808][ T2790]  ? cfb_fillrect+0x340/0x340 [cfbfillrect]
[   21.855821][ T2790]  vmw_fb_fillrect+0x12/0x30 [vmwgfx]
[   21.855828][ T2790]  bit_clear_margins+0xe0/0xf0 [fb]
[   21.855832][ T2790]  fbcon_clear_margins+0x4c/0x50 [fb]
[   21.855835][ T2790]  fbcon_switch+0x321/0x570 [fb]
[   21.855843][ T2790]  redraw_screen+0xe0/0x250
[   21.855847][ T2790]  fbcon_modechanged+0x1a3/0x1f0 [fb]
[   21.855851][ T2790]  fbcon_update_vcs+0x15/0x20 [fb]
[   21.855853][ T2790]  fb_set_var+0x364/0x3c0 [fb]
[   21.855863][ T2790]  do_fb_ioctl+0x2ff/0x3f0 [fb]
[   21.855866][ T2790]  ? find_held_lock+0x35/0xa0
[   21.855870][ T2790]  ? __audit_syscall_entry+0xd8/0x120
[   21.855888][ T2790]  ? kfree+0x25a/0x2b0
[   21.855944][ T2790]  fb_ioctl+0x2e/0x40 [fb]
[   21.855947][ T2790]  ksys_ioctl+0x86/0xc0
[   21.855950][ T2790]  ? do_syscall_64+0x20/0xa0
[   21.855952][ T2790]  __x64_sys_ioctl+0x15/0x20
[   21.855954][ T2790]  do_syscall_64+0x54/0xa0
[   21.855957][ T2790]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
[   21.855959][ T2790] RIP: 0033:0x7f9cef344307
[   21.855959][ T2790] Code: Bad RIP value.
[   21.855960][ T2790] RSP: 002b:00007ffddb6f2e48 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   21.855962][ T2790] RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007f9cef344307
[   21.855962][ T2790] RDX: 00007ffddb6f2e50 RSI: 0000000000004601 RDI: 0000000000000003
[   21.855963][ T2790] RBP: 0000000000000000 R08: 00007f9cef617e80 R09: 0000000000000000
[   21.855964][ T2790] R10: 00007ffddb6f28a0 R11: 0000000000000246 R12: 00000000004004f2
[   21.855964][ T2790] R13: 00007ffddb6f2fd0 R14: 0000000000000000 R15: 0000000000000000
[   21.855969][ T2790] Modules linked in: mousedev rapl evdev input_leds led_class mac_hid psmouse pcspkr xt_tcpudp af_packet ip6t_rpfilter ip6t_REJECT nf_reject_ipv6 ipt_REJECT nf_reject_ipv4 xt_conntrack ebtable_nat ip6table_nat ip6table_mangle ip6table_raw iptable_nat nf_nat iptable_mangle iptable_raw nf_conntrack rtc_cmos nf_defrag_ipv4 ip_set vmw_vmci nfnetlink ebtable_filter ebtables ip6table_filter ip6_tables iptable_filter bpfilter sg ac button i2c_piix4 intel_agp intel_gtt ip_tables x_tables ata_generic pata_acpi serio_raw atkbd libps2 vmwgfx drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea fb fbdev ttm drm ahci libahci i2c_core drm_panel_orientation_quirks backlight ata_piix e1000 agpgart libata i8042 serio unix ipv6 nf_defrag_ipv6
[   21.856040][ T2790] CR2: ffffb54440d3b000
[   21.856042][ T2790] ---[ end trace 083bab4cc8751a86 ]---
[   21.856044][ T2790] RIP: 0010:bitfill_aligned+0x87/0x120 [cfbfillrect]
----------
Tetsuo Handa July 11, 2020, 11:08 a.m. UTC | #3 
On 2020/07/11 15:16, Tetsuo Handa wrote:
> On 2020/07/10 19:56, Greg Kroah-Hartman wrote:
>> Where is the over/underflow happening here when we set a size to be so
>> small?  We should bound the size somewhere, and as you show, that's not
>> really working properly, right?
> 
> It is bit_clear_margins() where integer underflow is happening (4294966497 == 1 - 100 * 8),
> but the cause of this problem seems to be fbcon_startup() or vc_do_resize().
> 

A possible cause is that vc_resize(vc, 0, 0) fails to set vc->vc_cols == vc->vc_rows == 0
because of

  new_cols = (cols ? cols : vc->vc_cols);
  new_rows = (lines ? lines : vc->vc_rows);

exception. I don't know how user program referenced as

  /*
   * Change # of rows and columns (0 means unchanged/the size of fg_console)
   * [this is to be used together with some user program
   * like resize that changes the hardware videomode]
   */
  #define VC_RESIZE_MAXCOL (32767)
  #define VC_RESIZE_MAXROW (32767)

is utilizing this exception (this code predates the git repository). But since I
don't think that a console with 0 column and/or 0 row makes sense, the real root
cause might be that fb_set_var() fails to reject too small var.xres value for
keeping cols > 0 and too small var.yres value for keeping lines > 0.

Regardless, making "struct fbcon_ops"->clear_margins no-op when integer underflow
is detected (like below diff) helps avoiding crash. Can we apply this handy
protection assuming that vc->vc_cols * vc->vc_font.width and
vc->vc_rows * vc->vc_font.heigh do not cause integer overflow?

 drivers/video/fbdev/core/bitblit.c   |    4 ++--
 drivers/video/fbdev/core/fbcon_ccw.c |    4 ++--
 drivers/video/fbdev/core/fbcon_cw.c  |    4 ++--
 drivers/video/fbdev/core/fbcon_ud.c  |    4 ++--
 4 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/drivers/video/fbdev/core/bitblit.c b/drivers/video/fbdev/core/bitblit.c
index ca935c09a261..35ebeeccde4d 100644
--- a/drivers/video/fbdev/core/bitblit.c
+++ b/drivers/video/fbdev/core/bitblit.c
@@ -216,7 +216,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
 	region.color = color;
 	region.rop = ROP_COPY;
 
-	if (rw && !bottom_only) {
+	if ((int) rw > 0 && !bottom_only) {
 		region.dx = info->var.xoffset + rs;
 		region.dy = 0;
 		region.width = rw;
@@ -224,7 +224,7 @@ static void bit_clear_margins(struct vc_data *vc, struct fb_info *info,
 		info->fbops->fb_fillrect(info, &region);
 	}
 
-	if (bh) {
+	if ((int) bh > 0) {
 		region.dx = info->var.xoffset;
 		region.dy = info->var.yoffset + bs;
 		region.width = rs;
diff --git a/drivers/video/fbdev/core/fbcon_ccw.c b/drivers/video/fbdev/core/fbcon_ccw.c
index dfa9a8aa4509..78f3a5621478 100644
--- a/drivers/video/fbdev/core/fbcon_ccw.c
+++ b/drivers/video/fbdev/core/fbcon_ccw.c
@@ -201,7 +201,7 @@ static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
 	region.color = color;
 	region.rop = ROP_COPY;
 
-	if (rw && !bottom_only) {
+	if ((int) rw > 0 && !bottom_only) {
 		region.dx = 0;
 		region.dy = info->var.yoffset;
 		region.height = rw;
@@ -209,7 +209,7 @@ static void ccw_clear_margins(struct vc_data *vc, struct fb_info *info,
 		info->fbops->fb_fillrect(info, &region);
 	}
 
-	if (bh) {
+	if ((int) bh > 0) {
 		region.dx = info->var.xoffset + bs;
 		region.dy = 0;
                 region.height = info->var.yres_virtual;
diff --git a/drivers/video/fbdev/core/fbcon_cw.c b/drivers/video/fbdev/core/fbcon_cw.c
index ce08251bfd38..fd098ff17574 100644
--- a/drivers/video/fbdev/core/fbcon_cw.c
+++ b/drivers/video/fbdev/core/fbcon_cw.c
@@ -184,7 +184,7 @@ static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
 	region.color = color;
 	region.rop = ROP_COPY;
 
-	if (rw && !bottom_only) {
+	if ((int) rw > 0 && !bottom_only) {
 		region.dx = 0;
 		region.dy = info->var.yoffset + rs;
 		region.height = rw;
@@ -192,7 +192,7 @@ static void cw_clear_margins(struct vc_data *vc, struct fb_info *info,
 		info->fbops->fb_fillrect(info, &region);
 	}
 
-	if (bh) {
+	if ((int) bh > 0) {
 		region.dx = info->var.xoffset;
 		region.dy = info->var.yoffset;
                 region.height = info->var.yres;
diff --git a/drivers/video/fbdev/core/fbcon_ud.c b/drivers/video/fbdev/core/fbcon_ud.c
index 1936afc78fec..e165a3fad29a 100644
--- a/drivers/video/fbdev/core/fbcon_ud.c
+++ b/drivers/video/fbdev/core/fbcon_ud.c
@@ -231,7 +231,7 @@ static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
 	region.color = color;
 	region.rop = ROP_COPY;
 
-	if (rw && !bottom_only) {
+	if ((int) rw > 0 && !bottom_only) {
 		region.dy = 0;
 		region.dx = info->var.xoffset;
 		region.width  = rw;
@@ -239,7 +239,7 @@ static void ud_clear_margins(struct vc_data *vc, struct fb_info *info,
 		info->fbops->fb_fillrect(info, &region);
 	}
 
-	if (bh) {
+	if ((int) bh > 0) {
 		region.dy = info->var.yoffset;
 		region.dx = info->var.xoffset;
                 region.height  = bh;
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/cfbfillrect.c b/drivers/video/fbdev/core/cfbfillrect.c
index ba9f58b2a5e8..57e4c2d1bcc0 100644
--- a/drivers/video/fbdev/core/cfbfillrect.c
+++ b/drivers/video/fbdev/core/cfbfillrect.c
@@ -321,6 +321,9 @@  void cfb_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
 			fill_op32 = bitfill_aligned;
 			break;
 		}
+		if (fill_op32 == bitfill_aligned)
+			printk(KERN_DEBUG "height=%lu width=%lu bpp=%u bits=%u bytes=%u dst=%px dst_idx=%u p->fix.line_length=%u\n",
+			       height, width, bpp, bits, bytes, dst, dst_idx, p->fix.line_length);
 		while (height--) {
 			dst += dst_idx >> (ffs(bits) - 1);
 			dst_idx &= (bits - 1);