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.

This issue has already been fixed by commit eabb03293087 ("fbdev: Refactoring the fbcon packed pixel drawing routines") on v6.15-rc1, but it still exists in the stable version.

It was unclear if there were other scenarios for this issue, and I tried to add pr_err in sys_fillrect. But as Helge pointed out[1], sys_fillrect is on the console printing code path and adding printing here might cause infinite loop. So let's just fix the known scenario.

Fix it by moving set_blitting_type() to the visible area of the VC.

Link: https://lore.kernel.org/all/aef7d5fd-2926-4c58-b720-4af58aa380d3@gmx.de/ [1]

CC: stable@vger.kernel.org # for stable-6.6, 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 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 78a5b22c8d15..8139ac8a666f 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);