On Tue, May 16, 2017 at 09:02:29PM +1000, Michael Ellerman wrote:
> Breno Leitao <lei...@debian.org> writes:
>
> > Hello,
> >
> > Kernel 4.12-rc1 is showing a bug when I try it on a POWER8 virtual
> > machine. Justing SSHing into the machine causes this issue.
> >
> > [23.138124] usercopy: kernel memory overwrite attempt detected to
> > d000000003d80030 (mm_struct) (560 bytes)
> > [23.138195] ------------[ cut here ]------------
> > [23.138229] kernel BUG at mm/usercopy.c:72!
> > [23.138252] Oops: Exception in kernel mode, sig: 5 [#3]
> > [23.138280] SMP NR_CPUS=2048
> > [23.138280] NUMA
> > [23.138302] pSeries
> > [23.138330] Modules linked in:
> > [23.138354] CPU: 4 PID: 2215 Comm: sshd Tainted: G D
> > 4.12.0-rc1+ #9
> > [23.138395] task: c0000001e272dc00 task.stack: c0000001e27b0000
> > [23.138430] NIP: c000000000342358 LR: c000000000342354 CTR:
> > c0000000006eb060
> > [23.138472] REGS: c0000001e27b3a00 TRAP: 0700 Tainted: G D
> > (4.12.0-rc1+)
> > [23.138513] MSR: 8000000000029033 <SF,EE,ME,IR,DR,RI,LE>
> > [23.138517] CR: 28004222 XER: 20000000
> > [23.138565] CFAR: c000000000b34500 SOFTE: 1
> > [23.138565] GPR00: c000000000342354 c0000001e27b3c80 c00000000142a000
> > 000000000000005e
> > [23.138565] GPR04: c0000001ffe0ade8 c0000001ffe21bf8 2920283536302062
> > 79746573290d0a74
> > [23.138565] GPR08: 0000000000000007 c000000000f61864 00000001feeb0000
> > 3064206f74206465
> > [23.138565] GPR12: 0000000000004400 c00000000fb42600 0000000000000015
> > 00000000545bdc40
> > [23.138565] GPR16: 00000000545c49c8 000001000b4b8890 00007ffff78c26f0
> > 00000000545cf000
> > [23.138565] GPR20: 00000000546109c8 000000000000c7e8 0000000054610010
> > 00007ffff78c22e8
> > [23.138565] GPR24: 00000000545c8c40 c0000000ff6bcef0 c0000000001e5220
> > 0000000000000230
> > [23.138565] GPR28: d000000003d80260 0000000000000000 0000000000000230
> > d000000003d80030
> > [23.138920] NIP [c000000000342358] __check_object_size+0x88/0x2d0
> > [23.138956] LR [c000000000342354] __check_object_size+0x84/0x2d0
> > [23.138990] Call Trace:
> > [23.139006] [c0000001e27b3c80] [c000000000342354]
> > __check_object_size+0x84/0x2d0 (unreliable)
> > [23.139056] [c0000001e27b3d00] [c0000000009f5ba8]
> > bpf_prog_create_from_user+0xa8/0x1a0
> > [23.139099] [c0000001e27b3d60] [c0000000001e5d30] do_seccomp+0x120/0x720
> > [23.139136] [c0000001e27b3dd0] [c0000000000fd53c] SyS_prctl+0x2ac/0x6b0
> > [23.139172] [c0000001e27b3e30] [c00000000000af84] system_call+0x38/0xe0
> > [23.139218] Instruction dump:
> > [23.139240] 60000000 60420000 3c82ff94 3ca2ff9d 38841788 38a5e868
> > 3c62ff95 7fc8f378
> > [23.139283] 7fe6fb78 386310c0 487f2169 60000000 <0fe00000> 60420000
> > 2ba30010 409d018c
> > [23.139328] ---[ end trace 1a1dc952a4b7c4af ]---
>
> Do you have any idea what is calling seccomp() and triggering the bug?
This bug is hit using several path, not only via seccomp. This is
another path, via vfs_read, that triggers the bug:
[ 370.154307] usercopy: kernel memory exposure attempt detected from
d000000003d6007c (vm_area_struct) (6 bytes)
[ 370.154373] ------------[ cut here ]------------
[ 370.154402] kernel BUG at mm/usercopy.c:72!
[ 370.154425] Oops: Exception in kernel mode, sig: 5 [#4]
<snip>
[370.155220] [c0000001d30efab0] [c000000000342354]
__check_object_size+0x84/0x2b0 (unreliable)
[370.155272] [c0000001d30efb30] [c0000000006c96cc]
copy_from_read_buf+0xac/0x1e0
[370.155315] [c0000001d30efba0] [c0000000006ccbc4]
n_tty_read+0x324/0x920
[370.155351] [c0000001d30efcb0] [c0000000006c4c50] tty_read+0xc0/0x180
[370.155387] [c0000001d30efd00] [c000000000347f64] __vfs_read+0x44/0x1a0
[370.155424] [c0000001d30efd90] [c0000000003499ac] vfs_read+0xbc/0x1b0
[370.155460] [c0000001d30efde0] [c00000000034b6f8] SyS_read+0x68/0x110
[370.155497] [c0000001d30efe30] [c00000000000af84] system_call+0x38/0xe0
Anyway, I see the seccomp() path issue when I log into the system using SSH,
and the issue with tty_read() just during the system boot.
> I run the BPF and seccomp test suites, and I haven't seen this.
Do you have the hardening options enabled? For example, I do not
reproduce this problem if I do not set CONFIG_HARDENED_USERCOPY=y.
