Re: KASAN: use-after-free Read in vt_do_kdgkb_ioctl

From: Greg KH
Date: Wed Mar 18 2020 - 06:06:57 EST

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On Mon, Feb 24, 2020 at 09:00:28PM +0800, Hillf Danton wrote:
>
> On Mon, 24 Feb 2020 01:18:14 -0800
> > syzbot found the following crash on:
> >
> > HEAD commit: 54dedb5b Merge tag 'for-linus-5.6-rc3-tag' of git://git.ke..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=100403d9e00000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=3b8906eb6a7d6028
> > dashboard link: https://syzkaller.appspot.com/bug?extid=a58bfd517766aef83043
> > compiler: gcc (GCC) 9.0.0 20181231 (experimental)
> >
> > Unfortunately, I don't have any reproducer for this crash yet.
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+a58bfd517766aef83043@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > ==================================================================
> > BUG: KASAN: use-after-free in vt_do_kdgkb_ioctl+0xb24/0xb50 drivers/tty/vt/keyboard.c:2025
> > Read of size 1 at addr ffff8880a4a8c801 by task syz-executor.4/27890
> >
> > CPU: 1 PID: 27890 Comm: syz-executor.4 Not tainted 5.6.0-rc2-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > Call Trace:
> > __dump_stack lib/dump_stack.c:77 [inline]
> > dump_stack+0x197/0x210 lib/dump_stack.c:118
> > print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374
> > __kasan_report.cold+0x1b/0x32 mm/kasan/report.c:506
> > kasan_report+0x12/0x20 mm/kasan/common.c:641
> > __asan_report_load1_noabort+0x14/0x20 mm/kasan/generic_report.c:132
> > vt_do_kdgkb_ioctl+0xb24/0xb50 drivers/tty/vt/keyboard.c:2025
> > vt_ioctl+0x47e/0x26c0 drivers/tty/vt/vt_ioctl.c:549
> > tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
> > vfs_ioctl fs/ioctl.c:47 [inline]
> > ksys_ioctl+0x123/0x180 fs/ioctl.c:763
> > __do_sys_ioctl fs/ioctl.c:772 [inline]
> > __se_sys_ioctl fs/ioctl.c:770 [inline]
> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
> > do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> > RIP: 0033:0x45c429
> > Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007f0f2868cc78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> > RAX: ffffffffffffffda RBX: 00007f0f2868d6d4 RCX: 000000000045c429
> > RDX: 0000000020000200 RSI: 0000000000004b48 RDI: 0000000000000003
> > RBP: 000000000076bf20 R08: 0000000000000000 R09: 0000000000000000
> > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff
> > R13: 000000000000041a R14: 00000000004c676d R15: 000000000076bf2c
> >
> > Allocated by task 1548:
> > save_stack+0x23/0x90 mm/kasan/common.c:72
> > set_track mm/kasan/common.c:80 [inline]
> > __kasan_kmalloc mm/kasan/common.c:515 [inline]
> > __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:488
> > kasan_kmalloc+0x9/0x10 mm/kasan/common.c:529
> > __do_kmalloc mm/slab.c:3656 [inline]
> > __kmalloc+0x163/0x770 mm/slab.c:3665
> > kmalloc include/linux/slab.h:560 [inline]
> > vt_do_kdgkb_ioctl+0x3d1/0xb50 drivers/tty/vt/keyboard.c:2078
> > vt_ioctl+0x47e/0x26c0 drivers/tty/vt/vt_ioctl.c:549
> > tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
> > vfs_ioctl fs/ioctl.c:47 [inline]
> > ksys_ioctl+0x123/0x180 fs/ioctl.c:763
> > __do_sys_ioctl fs/ioctl.c:772 [inline]
> > __se_sys_ioctl fs/ioctl.c:770 [inline]
> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
> > do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > Freed by task 27892:
> > save_stack+0x23/0x90 mm/kasan/common.c:72
> > set_track mm/kasan/common.c:80 [inline]
> > kasan_set_free_info mm/kasan/common.c:337 [inline]
> > __kasan_slab_free+0x102/0x150 mm/kasan/common.c:476
> > kasan_slab_free+0xe/0x10 mm/kasan/common.c:485
> > __cache_free mm/slab.c:3426 [inline]
> > kfree+0x10a/0x2c0 mm/slab.c:3757
> > vt_do_kdgkb_ioctl+0x5b4/0xb50 drivers/tty/vt/keyboard.c:2104
> > vt_ioctl+0x47e/0x26c0 drivers/tty/vt/vt_ioctl.c:549
> > tty_ioctl+0xa37/0x14f0 drivers/tty/tty_io.c:2660
> > vfs_ioctl fs/ioctl.c:47 [inline]
> > ksys_ioctl+0x123/0x180 fs/ioctl.c:763
> > __do_sys_ioctl fs/ioctl.c:772 [inline]
> > __se_sys_ioctl fs/ioctl.c:770 [inline]
> > __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:770
> > do_syscall_64+0xfa/0x790 arch/x86/entry/common.c:294
> > entry_SYSCALL_64_after_hwframe+0x49/0xbe
> >
> > The buggy address belongs to the object at ffff8880a4a8c800
> > which belongs to the cache kmalloc-1k of size 1024
> > The buggy address is located 1 bytes inside of
> > 1024-byte region [ffff8880a4a8c800, ffff8880a4a8cc00)
> > The buggy address belongs to the page:
> > page:ffffea000292a300 refcount:1 mapcount:0 mapping:ffff8880aa400c40 index:0x0
> > flags: 0xfffe0000000200(slab)
> > raw: 00fffe0000000200 ffffea00026aa6c8 ffffea000210b1c8 ffff8880aa400c40
> > raw: 0000000000000000 ffff8880a4a8c000 0000000100000002 0000000000000000
> > page dumped because: kasan: bad access detected
> >
> > Memory state around the buggy address:
> > ffff8880a4a8c700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > ffff8880a4a8c780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
> > >ffff8880a4a8c800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ^
> > ffff8880a4a8c880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ffff8880a4a8c900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> > ==================================================================
>
> Allocate a tmp buf for duplicating the string under lock and use it
> outside lock.
>
> --- a/drivers/tty/vt/keyboard.c
> +++ b/drivers/tty/vt/keyboard.c
> @@ -1995,7 +1995,7 @@ int vt_do_kdgkb_ioctl(int cmd, struct kb
> int delta;
> char *first_free, *fj, *fnw;
> int i, j, k;
> - int ret;
> + int ret = 0;
> unsigned long flags;
>
> if (!capable(CAP_SYS_TTY_CONFIG))
> @@ -2021,18 +2021,45 @@ int vt_do_kdgkb_ioctl(int cmd, struct kb
> a struct member */
> up = user_kdgkb->kb_string;
> p = func_table[i];
> - if(p)
> + if (p) {
> + char *tmp_buf = kzalloc(sz + 1, GFP_KERNEL);
> +
> + if (!tmp_buf) {
> + ret = -ENOMEM;
> + goto reterr;
> + }
> +
> + spin_lock_irqsave(&func_buf_lock, flags);
> + p = func_table[i];
> + if (p) {
> + __kernel_size_t len = strlen(p);
> + if (sz < len) {
> + ret = -EOVERFLOW;
> + p = NULL;
> + } else {
> + memcpy(tmp_buf, p, len);
> + p = tmp_buf;
> + }
> + }
> + spin_unlock_irqrestore(&func_buf_lock, flags);
> + if (!p)
> + goto free_buf;
> +
> for ( ; *p && sz; p++, sz--)
> if (put_user(*p, up++)) {
> ret = -EFAULT;
> - goto reterr;
> + goto free_buf;
> }
> - if (put_user('\0', up)) {
> - ret = -EFAULT;
> - goto reterr;
> +
> +free_buf:
> + kfree(tmp_buf);
> + if (ret)
> + goto reterr;
> }
> - kfree(kbs);
> - return ((p && *p) ? -EOVERFLOW : 0);
> +
> + if (put_user('\0', up))
> + ret = -EFAULT;
> + goto reterr;
> case KDSKBSENT:
> if (!perm) {
> ret = -EPERM;
>

What ever happened to this? Did it fix the issue? If so, can you
resend this as a "real" patch I can apply?

thanks,

greg k-h

Next message: Lars-Peter Clausen: "Re: [PATCH v3 2/4] iio: accel: adxl372: add event interface"
Previous message: Baolin Wang: "Re: [PATCH v2 2/2] serial: sprd: cleanup the sprd_port for error case"
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