5.4-stable review patch. If anyone has any objections, please let me know.
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From: GONG Ruiqi gongruiqi1@huawei.com
commit 864f9963ec6b4b76d104d595ba28110b87158003 upstream.
Our in-house Syzkaller reported the following BUG (twice), which we believed was the same issue with [1]:
================================================================== BUG: KASAN: slab-out-of-bounds in vcs_scr_readw+0xc2/0xd0 drivers/tty/vt/vt.c:4740 Read of size 2 at addr ffff88800f5bef60 by task syz.7.2620/12393 ... Call Trace: <TASK> __dump_stack lib/dump_stack.c:88 [inline] dump_stack_lvl+0x72/0xa0 lib/dump_stack.c:106 print_address_description.constprop.0+0x6b/0x3d0 mm/kasan/report.c:364 print_report+0xba/0x280 mm/kasan/report.c:475 kasan_report+0xa9/0xe0 mm/kasan/report.c:588 vcs_scr_readw+0xc2/0xd0 drivers/tty/vt/vt.c:4740 vcs_write_buf_noattr drivers/tty/vt/vc_screen.c:493 [inline] vcs_write+0x586/0x840 drivers/tty/vt/vc_screen.c:690 vfs_write+0x219/0x960 fs/read_write.c:584 ksys_write+0x12e/0x260 fs/read_write.c:639 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 ... </TASK>
Allocated by task 5614: kasan_save_stack+0x20/0x40 mm/kasan/common.c:45 kasan_set_track+0x25/0x30 mm/kasan/common.c:52 ____kasan_kmalloc mm/kasan/common.c:374 [inline] __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383 kasan_kmalloc include/linux/kasan.h:201 [inline] __do_kmalloc_node mm/slab_common.c:1007 [inline] __kmalloc+0x62/0x140 mm/slab_common.c:1020 kmalloc include/linux/slab.h:604 [inline] kzalloc include/linux/slab.h:721 [inline] vc_do_resize+0x235/0xf40 drivers/tty/vt/vt.c:1193 vgacon_adjust_height+0x2d4/0x350 drivers/video/console/vgacon.c:1007 vgacon_font_set+0x1f7/0x240 drivers/video/console/vgacon.c:1031 con_font_set drivers/tty/vt/vt.c:4628 [inline] con_font_op+0x4da/0xa20 drivers/tty/vt/vt.c:4675 vt_k_ioctl+0xa10/0xb30 drivers/tty/vt/vt_ioctl.c:474 vt_ioctl+0x14c/0x1870 drivers/tty/vt/vt_ioctl.c:752 tty_ioctl+0x655/0x1510 drivers/tty/tty_io.c:2779 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:871 [inline] __se_sys_ioctl+0x12d/0x190 fs/ioctl.c:857 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
Last potentially related work creation: kasan_save_stack+0x20/0x40 mm/kasan/common.c:45 __kasan_record_aux_stack+0x94/0xa0 mm/kasan/generic.c:492 __call_rcu_common.constprop.0+0xc3/0xa10 kernel/rcu/tree.c:2713 netlink_release+0x620/0xc20 net/netlink/af_netlink.c:802 __sock_release+0xb5/0x270 net/socket.c:663 sock_close+0x1e/0x30 net/socket.c:1425 __fput+0x408/0xab0 fs/file_table.c:384 __fput_sync+0x4c/0x60 fs/file_table.c:465 __do_sys_close fs/open.c:1580 [inline] __se_sys_close+0x68/0xd0 fs/open.c:1565 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
Second to last potentially related work creation: kasan_save_stack+0x20/0x40 mm/kasan/common.c:45 __kasan_record_aux_stack+0x94/0xa0 mm/kasan/generic.c:492 __call_rcu_common.constprop.0+0xc3/0xa10 kernel/rcu/tree.c:2713 netlink_release+0x620/0xc20 net/netlink/af_netlink.c:802 __sock_release+0xb5/0x270 net/socket.c:663 sock_close+0x1e/0x30 net/socket.c:1425 __fput+0x408/0xab0 fs/file_table.c:384 task_work_run+0x154/0x240 kernel/task_work.c:239 exit_task_work include/linux/task_work.h:45 [inline] do_exit+0x8e5/0x1320 kernel/exit.c:874 do_group_exit+0xcd/0x280 kernel/exit.c:1023 get_signal+0x1675/0x1850 kernel/signal.c:2905 arch_do_signal_or_restart+0x80/0x3b0 arch/x86/kernel/signal.c:310 exit_to_user_mode_loop kernel/entry/common.c:111 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline] __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0x1b3/0x1e0 kernel/entry/common.c:218 do_syscall_64+0x66/0x110 arch/x86/entry/common.c:87 entry_SYSCALL_64_after_hwframe+0x78/0xe2
The buggy address belongs to the object at ffff88800f5be000 which belongs to the cache kmalloc-2k of size 2048 The buggy address is located 2656 bytes to the right of allocated 1280-byte region [ffff88800f5be000, ffff88800f5be500)
...
Memory state around the buggy address: ffff88800f5bee00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88800f5bee80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88800f5bef00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^ ffff88800f5bef80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc ffff88800f5bf000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ==================================================================
By analyzing the vmcore, we found that vc->vc_origin was somehow placed one line prior to vc->vc_screenbuf when vc was in KD_TEXT mode, and further writings to /dev/vcs caused out-of-bounds reads (and writes right after) in vcs_write_buf_noattr().
Our further experiments show that in most cases, vc->vc_origin equals to vga_vram_base when the console is in KD_TEXT mode, and it's around vc->vc_screenbuf for the KD_GRAPHICS mode. But via triggerring a TIOCL_SETVESABLANK ioctl beforehand, we can make vc->vc_origin be around vc->vc_screenbuf while the console is in KD_TEXT mode, and then by writing the special 'ESC M' control sequence to the tty certain times (depends on the value of `vc->state.y - vc->vc_top`), we can eventually move vc->vc_origin prior to vc->vc_screenbuf. Here's the PoC, tested on QEMU:
``` int main() { const int RI_NUM = 10; // should be greater than `vc->state.y - vc->vc_top` int tty_fd, vcs_fd; const char *tty_path = "/dev/tty0"; const char *vcs_path = "/dev/vcs"; const char escape_seq[] = "\x1bM"; // ESC + M const char trigger_seq[] = "Let's trigger an OOB write."; struct vt_sizes vt_size = { 70, 2 }; int blank = TIOCL_BLANKSCREEN;
tty_fd = open(tty_path, O_RDWR);
char vesa_mode[] = { TIOCL_SETVESABLANK, 1 }; ioctl(tty_fd, TIOCLINUX, vesa_mode);
ioctl(tty_fd, TIOCLINUX, &blank); ioctl(tty_fd, VT_RESIZE, &vt_size);
for (int i = 0; i < RI_NUM; ++i) write(tty_fd, escape_seq, sizeof(escape_seq) - 1);
vcs_fd = open(vcs_path, O_RDWR); write(vcs_fd, trigger_seq, sizeof(trigger_seq));
close(vcs_fd); close(tty_fd); return 0; } ```
To solve this problem, add an address range validation check in vgacon_scroll(), ensuring vc->vc_origin never precedes vc_screenbuf.
Reported-by: syzbot+9c09fda97a1a65ea859b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=9c09fda97a1a65ea859b [1] Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") Cc: stable@vger.kernel.org Co-developed-by: Yi Yang yiyang13@huawei.com Signed-off-by: Yi Yang yiyang13@huawei.com Signed-off-by: GONG Ruiqi gongruiqi1@huawei.com Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/video/console/vgacon.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/video/console/vgacon.c +++ b/drivers/video/console/vgacon.c @@ -1198,7 +1198,7 @@ static bool vgacon_scroll(struct vc_data c->vc_screenbuf_size - delta); c->vc_origin = vga_vram_end - c->vc_screenbuf_size; vga_rolled_over = 0; - } else + } else if (oldo - delta >= (unsigned long)c->vc_screenbuf) c->vc_origin -= delta; c->vc_scr_end = c->vc_origin + c->vc_screenbuf_size; scr_memsetw((u16 *) (c->vc_origin), c->vc_video_erase_char,