[PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[Gu Bowen]

There was an out-of-bounds issue found by syzkaller test on v6.6.

BUG: unable to handle page fault for address: ffffc90000c3f000
PGD 100000067 P4D 100000067 PUD 100c80067 PMD 10ac1c067 PTE 0
Oops: 0002 [#1] PREEMPT SMP KASAN PTI
CPU: 3 PID: 6521 Comm: syz.3.1365 Not tainted 6.6.0+ #82
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
RIP: 0010:memset64 arch/x86/include/asm/string_64.h:58 [inline]
RIP: 0010:memset_l include/linux/string.h:168 [inline]
RIP: 0010:bitfill_aligned drivers/video/fbdev/core/sysfillrect.c:53 [inline]
RIP: 0010:bitfill_aligned+0x144/0x1c0 drivers/video/fbdev/core/sysfillrect.c:25
Code: 23 04 24 48 31 d0 49 89 46 f8 44 89 e0 44 29 f8 29 c3 e8 9f 39 49 fe 89 d8 31 d2 4c 89 f7 41 f7 f4 48 89 c3 48 89 c1 48 89 e8 <f3> 48 ab 31 ff 4c 89 ee e8 df 2f 49 fe 4d 85 ed 0f 84 6b ff ff ff
RSP: 0018:ffff888119ce7418 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000180 RCX: 0000000000000180
RDX: 0000000000000000 RSI: ffffc90003873000 RDI: ffffc90000c3f000
RBP: 0000000000000000 R08: 0000000000006000 R09: 0000000000000040
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000040
R13: 0000000000000000 R14: ffffc90000c3f000 R15: 0000000000000000
FS:  00007f1704b926c0(0000) GS:ffff8881f5980000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffc90000c3f000 CR3: 00000001230d0002 CR4: 0000000000770ee0
DR0: 0000000000000000 DR1: 000000000000e000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
PKRU: 80000000
Call Trace:
 <TASK>
 sys_fillrect+0x429/0x830 drivers/video/fbdev/core/sysfillrect.c:281
 drm_fbdev_generic_defio_fillrect+0x27/0x140 drivers/gpu/drm/drm_fbdev_generic.c:37
 bit_clear+0x183/0x220 drivers/video/fbdev/core/bitblit.c:73
 __fbcon_clear+0x5ea/0x670 drivers/video/fbdev/core/fbcon.c:1281
 fbcon_scroll+0x41e/0x560 drivers/video/fbdev/core/fbcon.c:1847
 con_scroll+0x464/0x6a0 drivers/tty/vt/vt.c:577
 lf+0x274/0x2d0 drivers/tty/vt/vt.c:1461
 do_con_trol+0x5ea/0x3d80 drivers/tty/vt/vt.c:2149
 do_con_write+0x780/0x10c0 drivers/tty/vt/vt.c:2905
 con_write+0x28/0xc0 drivers/tty/vt/vt.c:3245
 do_output_char+0x5de/0x850 drivers/tty/n_tty.c:433
 process_output drivers/tty/n_tty.c:500 [inline]
 n_tty_write+0x442/0xb00 drivers/tty/n_tty.c:2406
 iterate_tty_write+0x2b5/0x630 drivers/tty/tty_io.c:1017
 file_tty_write.constprop.0+0x20c/0x3b0 drivers/tty/tty_io.c:1088
 call_write_iter include/linux/fs.h:2085 [inline]
 do_iter_readv_writev+0x210/0x3c0 fs/read_write.c:737
 do_iter_write+0x181/0x4e0 fs/read_write.c:862
 vfs_writev+0x15b/0x4d0 fs/read_write.c:935
 do_writev+0x136/0x370 fs/read_write.c:978
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x59/0x110 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x78/0xe2

When the virtual console is rotated in the backend state, it can lead to
inconsistencies between the size of the virtual console's size and its
hook functions. In such cases, clearing the screen may result in
out-of-bounds issue.

Fix it by adding a check in sys_fillrect() and moving set_blitting_type()
to the visible area of the VC.

CC: stable@vger.kernel.org      # fbdev had been refactored on 6.15-rc1
Fixes: 68648ed1f58d ("fbdev: add drawing functions for framebuffers in system RAM")
Signed-off-by: Gu Bowen <gubowen5@huawei.com>
---
 drivers/video/fbdev/core/fbcon.c       | 2 +-
 drivers/video/fbdev/core/sysfillrect.c | 6 ++++++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index b49f15a3442e..a6602f230089 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -2702,9 +2702,9 @@ static void fbcon_modechanged(struct fb_info *info)
 		return;
 
 	p = &fb_display[vc->vc_num];
-	set_blitting_type(vc, info);
 
 	if (con_is_visible(vc)) {
+		set_blitting_type(vc, info);
 		var_to_display(p, &info->var, info);
 		cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
 		rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c
index bcdcaeae6538..e5c4ee317b0b 100644
--- a/drivers/video/fbdev/core/sysfillrect.c
+++ b/drivers/video/fbdev/core/sysfillrect.c
@@ -238,6 +238,7 @@ void sys_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
 	u32 bpp = p->var.bits_per_pixel;
 	unsigned long *dst;
 	int dst_idx, left;
+	long dst_offset;
 
 	if (p->state != FBINFO_STATE_RUNNING)
 		return;
@@ -277,6 +278,11 @@ void sys_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
 		}
 		while (height--) {
 			dst += dst_idx >> (ffs(bits) - 1);
+			dst_offset = (unsigned long)dst - (unsigned long)p->screen_base;
+			if (dst_offset < 0 || dst_offset >= p->fix.smem_len) {
+				pr_err("dst offset out of bound: dst_offset(%ld)", dst_offset);
+				return;
+			}
 			dst_idx &= (bits - 1);
 			fill_op32(p, dst, dst_idx, pat, width*bpp, bits);
 			dst_idx += p->fix.line_length*8;
-- 
2.43.0

Re: [PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[Helge Deller]

On 11/12/25 08:32, Gu Bowen wrote:
> There was an out-of-bounds issue found by syzkaller test on v6.6.
> 
> BUG: unable to handle page fault for address: ffffc90000c3f000
> PGD 100000067 P4D 100000067 PUD 100c80067 PMD 10ac1c067 PTE 0
> Oops: 0002 [#1] PREEMPT SMP KASAN PTI
> CPU: 3 PID: 6521 Comm: syz.3.1365 Not tainted 6.6.0+ #82
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
> RIP: 0010:memset64 arch/x86/include/asm/string_64.h:58 [inline]
> RIP: 0010:memset_l include/linux/string.h:168 [inline]
> RIP: 0010:bitfill_aligned drivers/video/fbdev/core/sysfillrect.c:53 [inline]
> RIP: 0010:bitfill_aligned+0x144/0x1c0 drivers/video/fbdev/core/sysfillrect.c:25
> Code: 23 04 24 48 31 d0 49 89 46 f8 44 89 e0 44 29 f8 29 c3 e8 9f 39 49 fe 89 d8 31 d2 4c 89 f7 41 f7 f4 48 89 c3 48 89 c1 48 89 e8 <f3> 48 ab 31 ff 4c 89 ee e8 df 2f 49 fe 4d 85 ed 0f 84 6b ff ff ff
> RSP: 0018:ffff888119ce7418 EFLAGS: 00010246
> RAX: 0000000000000000 RBX: 0000000000000180 RCX: 0000000000000180
> RDX: 0000000000000000 RSI: ffffc90003873000 RDI: ffffc90000c3f000
> RBP: 0000000000000000 R08: 0000000000006000 R09: 0000000000000040
> R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000040
> R13: 0000000000000000 R14: ffffc90000c3f000 R15: 0000000000000000
> FS:  00007f1704b926c0(0000) GS:ffff8881f5980000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: ffffc90000c3f000 CR3: 00000001230d0002 CR4: 0000000000770ee0
> DR0: 0000000000000000 DR1: 000000000000e000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> PKRU: 80000000
> Call Trace:
>   <TASK>
>   sys_fillrect+0x429/0x830 drivers/video/fbdev/core/sysfillrect.c:281
>   drm_fbdev_generic_defio_fillrect+0x27/0x140 drivers/gpu/drm/drm_fbdev_generic.c:37
>   bit_clear+0x183/0x220 drivers/video/fbdev/core/bitblit.c:73
>   __fbcon_clear+0x5ea/0x670 drivers/video/fbdev/core/fbcon.c:1281
>   fbcon_scroll+0x41e/0x560 drivers/video/fbdev/core/fbcon.c:1847
>   con_scroll+0x464/0x6a0 drivers/tty/vt/vt.c:577
>   lf+0x274/0x2d0 drivers/tty/vt/vt.c:1461
>   do_con_trol+0x5ea/0x3d80 drivers/tty/vt/vt.c:2149
>   do_con_write+0x780/0x10c0 drivers/tty/vt/vt.c:2905
>   con_write+0x28/0xc0 drivers/tty/vt/vt.c:3245
>   do_output_char+0x5de/0x850 drivers/tty/n_tty.c:433
>   process_output drivers/tty/n_tty.c:500 [inline]
>   n_tty_write+0x442/0xb00 drivers/tty/n_tty.c:2406
>   iterate_tty_write+0x2b5/0x630 drivers/tty/tty_io.c:1017
>   file_tty_write.constprop.0+0x20c/0x3b0 drivers/tty/tty_io.c:1088
>   call_write_iter include/linux/fs.h:2085 [inline]
>   do_iter_readv_writev+0x210/0x3c0 fs/read_write.c:737
>   do_iter_write+0x181/0x4e0 fs/read_write.c:862
>   vfs_writev+0x15b/0x4d0 fs/read_write.c:935
>   do_writev+0x136/0x370 fs/read_write.c:978
>   do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>   do_syscall_64+0x59/0x110 arch/x86/entry/common.c:81
>   entry_SYSCALL_64_after_hwframe+0x78/0xe2
> 
> When the virtual console is rotated in the backend state, it can lead to
> inconsistencies between the size of the virtual console's size and its
> hook functions. In such cases, clearing the screen may result in
> out-of-bounds issue.
> 
> Fix it by adding a check in sys_fillrect() and moving set_blitting_type()
> to the visible area of the VC.
> 
> CC: stable@vger.kernel.org      # fbdev had been refactored on 6.15-rc1
> Fixes: 68648ed1f58d ("fbdev: add drawing functions for framebuffers in system RAM")
> Signed-off-by: Gu Bowen <gubowen5@huawei.com>
> ---
>   drivers/video/fbdev/core/fbcon.c       | 2 +-
>   drivers/video/fbdev/core/sysfillrect.c | 6 ++++++
>   2 files changed, 7 insertions(+), 1 deletion(-)


That patch does not apply to git head.
Can you try to reproduce with git head?

Helge

  
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index b49f15a3442e..a6602f230089 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -2702,9 +2702,9 @@ static void fbcon_modechanged(struct fb_info *info)
>   		return;
>   
>   	p = &fb_display[vc->vc_num];
> -	set_blitting_type(vc, info);
>   
>   	if (con_is_visible(vc)) {
> +		set_blitting_type(vc, info);
>   		var_to_display(p, &info->var, info);
>   		cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
>   		rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
> diff --git a/drivers/video/fbdev/core/sysfillrect.c b/drivers/video/fbdev/core/sysfillrect.c
> index bcdcaeae6538..e5c4ee317b0b 100644
> --- a/drivers/video/fbdev/core/sysfillrect.c
> +++ b/drivers/video/fbdev/core/sysfillrect.c
> @@ -238,6 +238,7 @@ void sys_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
>   	u32 bpp = p->var.bits_per_pixel;
>   	unsigned long *dst;
>   	int dst_idx, left;
> +	long dst_offset;
>   
>   	if (p->state != FBINFO_STATE_RUNNING)
>   		return;
> @@ -277,6 +278,11 @@ void sys_fillrect(struct fb_info *p, const struct fb_fillrect *rect)
>   		}
>   		while (height--) {
>   			dst += dst_idx >> (ffs(bits) - 1);
> +			dst_offset = (unsigned long)dst - (unsigned long)p->screen_base;
> +			if (dst_offset < 0 || dst_offset >= p->fix.smem_len) {
> +				pr_err("dst offset out of bound: dst_offset(%ld)", dst_offset);
> +				return;
> +			}
>   			dst_idx &= (bits - 1);
>   			fill_op32(p, dst, dst_idx, pat, width*bpp, bits);
>   			dst_idx += p->fix.line_length*8;

Re: [PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[Gu Bowen]

Hi,

On 11/15/2025 3:21 AM, Helge Deller wrote:
> 
> That patch does not apply to git head.
> Can you try to reproduce with git head?
> 

fbdev has already been refactored by commit eabb03293087 ("fbdev: 
Refactoring the fbcon packed pixel drawing routines") on v6.15-rc1, so 
this issue no longer exists in the mainline version. Similar question 
has occurred in the past:

https://syzkaller.appspot.com/bug?extid=66bde8e1e4161d4b2cca

After the refactoring patch was merged, this issue did not reappear, but 
it still exists in the stable version.

BR,
Guber

Re: [PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[Helge Deller]

On 12/1/25 10:25, Gu Bowen wrote:
> Hi,
> 
> On 11/15/2025 3:21 AM, Helge Deller wrote:
>> 
>> That patch does not apply to git head. Can you try to reproduce
>> with git head?
>> 
> 
> fbdev has already been refactored by commit eabb03293087 ("fbdev:
> Refactoring the fbcon packed pixel drawing routines") on v6.15-rc1,
> so this issue no longer exists in the mainline version. Similar
> question has occurred in the past:
> 
> https://syzkaller.appspot.com/bug?extid=66bde8e1e4161d4b2cca
> 
> After the refactoring patch was merged, this issue did not reappear,
> but it still exists in the stable version.
Backporting commit eabb03293087 to 6.6 seems unrealistic.
So, maybe adding your patch to stable might make sense.

+	if (dst_offset < 0 || dst_offset >= p->fix.smem_len) {
+		pr_err("dst offset out of bound: dst_offset(%ld)", dst_offset);
+		return;

I don't like the pr_err() in here. I do understand that you want to print
that something wrong happened, but we are inside the console printing code.
I think we should just return in this case.

With that change we might ask Greg if he accepts this small patch for stable-6.6...

Helge

Re: [PATCH stable] fbdev: Fix out-of-bounds issue in sys_fillrect()

[Gu Bowen]

On 12/3/2025 4:05 AM, Helge Deller wrote:
> Backporting commit eabb03293087 to 6.6 seems unrealistic.
> So, maybe adding your patch to stable might make sense.
> 
> +    if (dst_offset < 0 || dst_offset >= p->fix.smem_len) {
> +        pr_err("dst offset out of bound: dst_offset(%ld)", dst_offset);
> +        return;
> 
> I don't like the pr_err() in here. I do understand that you want to print
> that something wrong happened, but we are inside the console printing code.
> I think we should just return in this case.
> 

Oh, you are right, I should not add pr_err() in here. Maybe we can use 
pr_info_once() instead if you don't mind.
I will send a new patch until I receive your feedback. Thanks!

BR,
Guber