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, ®ion); }
@@ -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, ®ion); } } 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] ----------