Re: tty, fbcon: use-after-free in fbcon_invert_region
From: Dmitry Vyukov <dvyukov@google.com>
Date: 2016-10-11 13:32:04
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On Tue, Oct 11, 2016 at 3:43 AM, Scot Doyle [off-list ref] wrote:
quoted hunk ↗ jump to hunk
On Fri, 7 Oct 2016, Dmitry Vyukov wrote:quoted
On Sat, Sep 3, 2016 at 9:20 PM, Dmitry Vyukov [off-list ref] wrote:quoted
Hello, The following program causes use-after-free in fbcon_invert_region: https://gist.githubusercontent.com/dvyukov/d657f9a9ca39f34c430dcf63ec1153ac/raw/04e1b94aef0fc9eb770d11373b568980ecaa7f34/gistfile1.txt ================================= BUG: KASAN: use-after-free in fbcon_invert_region+0x1cc/0x1f0 at addr ffff88006cc3f51e Read of size 2 by task a.out/4240 CPU: 0 PID: 4240 Comm: a.out Not tainted 4.8.0-rc3-next-20160825+ #10 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 ffffffff886b6fe0 ffff88003699f790 ffffffff82db3759 ffffffff8a0ae640 fffffbfff10d6dfc ffff88003e800100 ffff88006cc3f500 ffff88006cc3f520 0000000000000000 ffff88006cc3f51e ffff88003699f7b8 ffffffff81809e7c Call Trace: [<ffffffff8180a474>] __asan_report_load2_noabort+0x14/0x20 mm/kasan/report.c:325 [<ffffffff82fdbc8c>] fbcon_invert_region+0x1cc/0x1f0 drivers/video/console/fbcon.c:2750 [<ffffffff8327ce72>] invert_screen+0x192/0x630 drivers/tty/vt/vt.c:470 [< inline >] highlight drivers/tty/vt/selection.c:50 [<ffffffff8326037c>] clear_selection+0x4c/0x60 drivers/tty/vt/selection.c:76 [<ffffffff8327374e>] hide_cursor+0x24e/0x2d0 drivers/tty/vt/vt.c:599 [<ffffffff83276207>] redraw_screen+0x2e7/0x840 drivers/tty/vt/vt.c:682 [<ffffffff83278b0c>] vc_do_resize+0xebc/0x1160 drivers/tty/vt/vt.c:952 [<ffffffff83278eba>] vt_resize+0xaa/0xe0 drivers/tty/vt/vt.c:992 [< inline >] tiocswinsz drivers/tty/tty_io.c:2378 [<ffffffff83224e71>] tty_ioctl+0x10c1/0x21e0 drivers/tty/tty_io.c:2892 [< inline >] vfs_ioctl fs/ioctl.c:43 [<ffffffff818a1c6c>] do_vfs_ioctl+0x18c/0x1080 fs/ioctl.c:675 [< inline >] SYSC_ioctl fs/ioctl.c:690 [<ffffffff818a2bef>] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:681 [<ffffffff86e10480>] entry_SYSCALL_64_fastpath+0x23/0xc1I wonder if the text selection is outside the newly resized vc? Does this patch help?--- vt.c 2016-10-11 00:32:43.079605599 -0000 +++ vt.c.new 2016-10-11 00:36:12.744650759 -0000@@ -874,6 +874,9 @@ if (!newscreen) return -ENOMEM; + if (vc = sel_cons) + clear_selection(); + old_rows = vc->vc_rows; old_row_size = vc->vc_size_row;
This helped with the use-after-frees and out-of-bounds. Tested-by: Dmitry Vyukov <dvyukov@google.com> However, now the test program hanged in D unkillable stack on some kind of kernel deadlock. Don't know if it's induced by your patch, or just another bug. At least there are no vc_do_resize in stacks. # ps afxu | grep a.out root 6163 6.5 0.0 0 0 pts/0 Zl 13:25 0:00 | \_ [a.out] <defunct> # ls /proc/6163/task/ 6163 6191 6193 6194 6201 # cat /proc/6163/task/*/stack [< inline >] down_read_failed drivers/tty/tty_ldsem.c:241 [<ffffffff831b8da6>] __ldsem_down_read_nested+0x2a6/0x5b0 drivers/tty/tty_ldsem.c:332 [<ffffffff831b23f5>] tty_ldisc_ref_wait+0x35/0xb0 drivers/tty/tty_ldisc.c:274 [<ffffffff831962b7>] tty_write+0x177/0x840 drivers/tty/tty_io.c:1250 [<ffffffff8182c700>] __vfs_write+0x110/0x620 fs/read_write.c:510 [<ffffffff8182dc05>] vfs_write+0x175/0x4e0 fs/read_write.c:560 [< inline >] SYSC_write fs/read_write.c:607 [<ffffffff818314c9>] SyS_write+0xd9/0x1b0 fs/read_write.c:599 [<ffffffff86daf545>] entry_SYSCALL_64_fastpath+0x23/0xc6 arch/x86/entry/entry_64.S:208 [<ffffffffffffffff>] 0xffffffffffffffff [< inline >] down_read_failed drivers/tty/tty_ldsem.c:241 [<ffffffff831b8da6>] __ldsem_down_read_nested+0x2a6/0x5b0 drivers/tty/tty_ldsem.c:332 [<ffffffff831b23f5>] tty_ldisc_ref_wait+0x35/0xb0 drivers/tty/tty_ldisc.c:274 [<ffffffff831962b7>] tty_write+0x177/0x840 drivers/tty/tty_io.c:1250 [<ffffffff8182c700>] __vfs_write+0x110/0x620 fs/read_write.c:510 [<ffffffff8182dc05>] vfs_write+0x175/0x4e0 fs/read_write.c:560 [< inline >] SYSC_write fs/read_write.c:607 [<ffffffff818314c9>] SyS_write+0xd9/0x1b0 fs/read_write.c:599 [<ffffffff86daf545>] entry_SYSCALL_64_fastpath+0x23/0xc6 arch/x86/entry/entry_64.S:208 [<ffffffffffffffff>] 0xffffffffffffffff [< inline >] down_read_failed drivers/tty/tty_ldsem.c:241 [<ffffffff831b8da6>] __ldsem_down_read_nested+0x2a6/0x5b0 drivers/tty/tty_ldsem.c:332 [<ffffffff831b23f5>] tty_ldisc_ref_wait+0x35/0xb0 drivers/tty/tty_ldisc.c:274 [<ffffffff831962b7>] tty_write+0x177/0x840 drivers/tty/tty_io.c:1250 [<ffffffff8182c700>] __vfs_write+0x110/0x620 fs/read_write.c:510 [<ffffffff8182dc05>] vfs_write+0x175/0x4e0 fs/read_write.c:560 [< inline >] SYSC_write fs/read_write.c:607 [<ffffffff818314c9>] SyS_write+0xd9/0x1b0 fs/read_write.c:599 [<ffffffff86daf545>] entry_SYSCALL_64_fastpath+0x23/0xc6 arch/x86/entry/entry_64.S:208 [<ffffffffffffffff>] 0xffffffffffffffff [< inline >] down_read_failed drivers/tty/tty_ldsem.c:241 [<ffffffff831b8da6>] __ldsem_down_read_nested+0x2a6/0x5b0 drivers/tty/tty_ldsem.c:332 [<ffffffff831b23f5>] tty_ldisc_ref_wait+0x35/0xb0 drivers/tty/tty_ldisc.c:274 [<ffffffff8319def3>] tty_ioctl+0xc53/0x2180 drivers/tty/tty_io.c:2987 [< inline >] vfs_ioctl fs/ioctl.c:43 [<ffffffff8186bc31>] do_vfs_ioctl+0x191/0x1050 fs/ioctl.c:679 [< inline >] SYSC_ioctl fs/ioctl.c:694 [<ffffffff8186cb84>] SyS_ioctl+0x94/0xc0 fs/ioctl.c:685 [<ffffffff86daf545>] entry_SYSCALL_64_fastpath+0x23/0xc6 arch/x86/entry/entry_64.S:208 [<ffffffffffffffff>] 0xffffffffffffffff # cat /proc/6191/status Name: a.out Umask: 0022 State: D (disk sleep) Tgid: 6163 Ngid: 0 Pid: 6191 PPid: 6154 TracerPid: 0 Uid: 0 0 0 0 Gid: 0 0 0 0 FDSize: 256 Groups: 0 NStgid: 6163 NSpid: 6191 NSpgid: 6163 NSsid: 6154 VmPeak: 402244 kB VmSize: 402244 kB VmLck: 0 kB VmPin: 0 kB VmHWM: 3140 kB VmRSS: 3140 kB RssAnon: 2508 kB RssFile: 632 kB RssShmem: 0 kB VmData: 401072 kB VmStk: 136 kB VmExe: 832 kB VmLib: 8 kB VmPTE: 212 kB VmPMD: 12 kB VmSwap: 0 kB HugetlbPages: 0 kB Threads: 5 SigQ: 1/3150 SigPnd: 0000000000000100 ShdPnd: 0000000000000100 SigBlk: 0000000000000000 SigIgn: 0000000000000000 SigCgt: 0000000180000440 CapInh: 0000000000000000 CapPrm: 0000003fffffffff CapEff: 0000003fffffffff CapBnd: 0000003fffffffff CapAmb: 0000000000000000 Seccomp: 0 Cpus_allowed: f Cpus_allowed_list: 0-3 Mems_allowed: 00000000,00000003 Mems_allowed_list: 0-1 voluntary_ctxt_switches: 1 nonvoluntary_ctxt_switches: 0