[syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

[syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    691d401c7e0e Merge tag 'spi-fix-v6.18-rc3' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14607932580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=19d831c6d0386a9c
dashboard link: https://syzkaller.appspot.com/bug?extid=5a40432dfe8f86ee657a
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5eaccda03e4f/disk-691d401c.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0df5294a69bc/vmlinux-691d401c.xz
kernel image: https://storage.googleapis.com/syzbot-assets/f4f242731772/bzImage-691d401c.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5a40432dfe8f86ee657a@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
Write of size 8 at addr ffffc90003e99280 by task kworker/0:2/781

CPU: 0 UID: 0 PID: 781 Comm: kworker/0:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: events_power_efficient fb_flashcursor
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
 fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
 fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
 fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
 sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
 drm_fbdev_shmem_defio_imageblit+0x20/0x130 drivers/gpu/drm/drm_fbdev_shmem.c:38
 soft_cursor+0x524/0xa10 drivers/video/fbdev/core/softcursor.c:74
 bit_cursor+0xe8c/0x17e0 drivers/video/fbdev/core/bitblit.c:395
 fb_flashcursor drivers/video/fbdev/core/fbcon.c:401 [inline]
 fb_flashcursor+0x310/0x400 drivers/video/fbdev/core/fbcon.c:370
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc90003e99180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003e99200: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003e99280: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                   ^
 ffffc90003e99300: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003e99380: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


---
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#syz undup

Re: [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    e7c375b18160 Merge tag 'vfs-6.18-rc7.fixes' of gitolite.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15476692580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1cd7f786c0f5182f
dashboard link: https://syzkaller.appspot.com/bug?extid=5a40432dfe8f86ee657a
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=10a70332580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=173228b4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1fcb660703f1/disk-e7c375b1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4bf314965321/vmlinux-e7c375b1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/456b373fea36/bzImage-e7c375b1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5a40432dfe8f86ee657a@syzkaller.appspotmail.com

RDX: 0000000000000007 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fff34de03f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fd0417e5fa0 R14: 00007fd0417e5fa0 R15: 0000000000000003
 </TASK>
==================================================================
BUG: KASAN: vmalloc-out-of-bounds in fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
BUG: KASAN: vmalloc-out-of-bounds in fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
BUG: KASAN: vmalloc-out-of-bounds in sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
Write of size 8 at addr ffffc90003749fc0 by task syz.0.17/6037

CPU: 0 UID: 0 PID: 6037 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 fb_write_offset drivers/video/fbdev/core/sysmem.h:30 [inline]
 fb_bitmap_2ppw drivers/video/fbdev/core/fb_imageblit.h:364 [inline]
 fb_bitmap_imageblit drivers/video/fbdev/core/fb_imageblit.h:462 [inline]
 fb_imageblit drivers/video/fbdev/core/fb_imageblit.h:492 [inline]
 sys_imageblit+0x1a6f/0x1e60 drivers/video/fbdev/core/sysimgblt.c:24
 drm_fbdev_shmem_defio_imageblit+0x20/0x130 drivers/gpu/drm/drm_fbdev_shmem.c:38
 cw_putcs_aligned drivers/video/fbdev/core/fbcon_cw.c:110 [inline]
 cw_putcs+0x917/0xbb0 drivers/video/fbdev/core/fbcon_cw.c:158
 fbcon_putcs+0x387/0x450 drivers/video/fbdev/core/fbcon.c:1320
 do_update_region+0x2e9/0x3f0 drivers/tty/vt/vt.c:628
 redraw_screen+0x63f/0x760 drivers/tty/vt/vt.c:980
 fbcon_modechanged+0x456/0x6b0 drivers/video/fbdev/core/fbcon.c:2710
 fbcon_rotate drivers/video/fbdev/core/fbcon.c:228 [inline]
 rotate_store+0x258/0x2f0 drivers/video/fbdev/core/fbcon.c:3215
 dev_attr_store+0x58/0x80 drivers/base/core.c:2437
 sysfs_kf_write+0xf2/0x150 fs/sysfs/file.c:142
 kernfs_fop_write_iter+0x3af/0x570 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x7d3/0x11d0 fs/read_write.c:686
 ksys_write+0x12a/0x250 fs/read_write.c:738
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd04158f6c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff34de0398 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007fd0417e5fa0 RCX: 00007fd04158f6c9
RDX: 0000000000000007 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007fff34de03f0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fd0417e5fa0 R14: 00007fd0417e5fa0 R15: 0000000000000003
 </TASK>

The buggy address belongs to a vmalloc virtual mapping
Memory state around the buggy address:
 ffffc90003749e80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc90003749f00: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
>ffffc90003749f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
                                           ^
 ffffc9000374a000: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
 ffffc9000374a080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
==================================================================


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

[shaurya]

[-- Attachment #1: Type: text/plain, Size: 82 bytes --]

#syz test:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master

[-- Attachment #2: 0001-testing-my-fix.patch --]
[-- Type: text/x-patch, Size: 3132 bytes --]

From 188fc7eea4a00500a806b7b122d20289abc2bf00 Mon Sep 17 00:00:00 2001
From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
Date: Wed, 19 Nov 2025 15:44:51 +0530
Subject: [PATCH] testing my fix

Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
---
 drivers/video/fbdev/core/fb_imageblit.h | 66 +++++++++++++++++++++++--
 1 file changed, 62 insertions(+), 4 deletions(-)

diff --git a/drivers/video/fbdev/core/fb_imageblit.h b/drivers/video/fbdev/core/fb_imageblit.h
index 3b2bb4946505..aee7f4032164 100644
--- a/drivers/video/fbdev/core/fb_imageblit.h
+++ b/drivers/video/fbdev/core/fb_imageblit.h
@@ -485,11 +485,69 @@ static inline void fb_imageblit(struct fb_info *p, const struct fb_image *image)
 	struct fb_address dst = fb_address_init(p);
 	struct fb_reverse reverse = fb_reverse_init(p);
 	const u32 *palette = fb_palette(p);
+	struct fb_image clipped_image;
+	u32 max_x, max_y;
+	unsigned long max_offset_bytes;
+
+	/* Validate basic parameters */
+	if (!image || !p->screen_buffer || !p->screen_size || 
+	    !image->width || !image->height)
+		return;
+
+	/* Calculate maximum addressable coordinates based on virtual resolution and buffer size */
+	max_x = p->var.xres_virtual;
+	max_y = p->var.yres_virtual;
+	
+	/* Also check against actual buffer size to prevent vmalloc overflow */
+	{
+		unsigned long effective_width_bytes;
+		u32 right_edge = image->dx + image->width;
+
+		if (right_edge < image->dx)
+			right_edge = max_x;
+		else
+			right_edge = min(right_edge, max_x);
+
+		effective_width_bytes = (unsigned long)right_edge * bpp;
+		effective_width_bytes = (effective_width_bytes + 7) / 8;
+
+		if (effective_width_bytes > p->screen_size) {
+			max_y = 0;
+		} else if (p->fix.line_length) {
+			u32 max_lines = (p->screen_size - effective_width_bytes) /
+					p->fix.line_length + 1;
+			if (max_lines < max_y)
+				max_y = max_lines;
+		}
+	}
+
+	/* If image is completely outside bounds, skip it */
+	if (image->dx >= max_x || image->dy >= max_y)
+		return;
+
+	/* Create clipped image - clip to virtual resolution bounds */
+	clipped_image = *image;
+	
+	/* Clip width if it extends beyond right edge */
+	if (clipped_image.dx + clipped_image.width > max_x) {
+		if (clipped_image.dx < max_x)
+			clipped_image.width = max_x - clipped_image.dx;
+		else
+			return; /* completely outside */
+	}
+	
+	/* Clip height if it extends beyond bottom edge */
+	if (clipped_image.dy + clipped_image.height > max_y) {
+		if (clipped_image.dy < max_y)
+			clipped_image.height = max_y - clipped_image.dy;
+		else
+			return; /* completely outside */
+	}
 
-	fb_address_forward(&dst, image->dy * bits_per_line + image->dx * bpp);
+	fb_address_forward(&dst, clipped_image.dy * bits_per_line + clipped_image.dx * bpp);
 
-	if (image->depth == 1)
-		fb_bitmap_imageblit(image, &dst, bits_per_line, palette, bpp, reverse);
+	if (clipped_image.depth == 1)
+		fb_bitmap_imageblit(&clipped_image, &dst, bits_per_line, palette, bpp, reverse);
 	else
-		fb_color_imageblit(image, &dst, bits_per_line, palette, bpp, reverse);
+		fb_color_imageblit(&clipped_image, &dst, bits_per_line, palette, bpp, reverse);
 }
-- 
2.34.1

Re: [syzbot] [fbdev?] KASAN: vmalloc-out-of-bounds Write in imageblit (6)

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+5a40432dfe8f86ee657a@syzkaller.appspotmail.com
Tested-by: syzbot+5a40432dfe8f86ee657a@syzkaller.appspotmail.com

Tested on:

commit:         8b690556 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10921212580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=1cd7f786c0f5182f
dashboard link: https://syzkaller.appspot.com/bug?extid=5a40432dfe8f86ee657a
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=13a21212580000

Note: testing is done by a robot and is best-effort only.