Re: [PATCH v2] cgroup: align the comm length with TASK_COMM_LEN

[Kassey Li]

On 9/26/2022 10:09 PM, Steven Rostedt wrote:
> On Fri, 23 Sep 2022 15:51:05 +0800
> Kassey Li <quic_yingangl@xxxxxxxxxxx> wrote:
>
> > __string could get a dst string with length less than
> > TASK_COMM_LEN.
> >
> > A task->comm may change that can cause out of bounds access
> > for the dst string buffer, e.g in the call trace of below:
> >
> > Call trace:
> >
> >      dump_backtrace.cfi_jt+0x0/0x4
> >      show_stack+0x14/0x1c
> >      dump_stack+0xa0/0xd8
> >      die_callback+0x248/0x24c
> >      notify_die+0x7c/0xf8
> >      die+0xac/0x290
> >      die_kernel_fault+0x88/0x98
> >      die_kernel_fault+0x0/0x98
> >      do_page_fault+0xa0/0x544
> >      do_mem_abort+0x60/0x10c
> >      el1_da+0x1c/0xc4
>
> >      trace_event_raw_event_cgroup_migrate+0x124/0x170
>
> You're sure the above is on the strcpy()?
set PC to 0xffffffda401c47d4
and this reflect to the strcpy asm code of aarch64. (lib/string.c)

                         120|
  NSX:0000::FFFFFFDA401C47B8|B946C268 
                      ldr     w8,[x19,#0x6C0]   ; w8,[task,#1728]
  NSX:0000::FFFFFFDA401C47BC|79403809 
                      ldrh    w9,[x0,#0x1C]    ; w9,[entry,#28]
  NSX:0000::FFFFFFDA401C47C0|F10002FF 
                      cmp     x23,#0x0         ; x23,#0
  NSX:0000::FFFFFFDA401C47C4|B9001408 
                      str     w8,[x0,#0x14]    ; w8,[entry,#20]
  NSX:0000::FFFFFFDA401C47C8|8B090008 
                      add     x8,x0,x9         ; x8,entry,x9
  NSX:0000::FFFFFFDA401C47CC|9A970349 
                      csel    x9,x26,x23,eq
                            |
                            |
                          93|
  NSX:0000::FFFFFFDA401C47D0|3840152A 
                      ldrb    w10,[x9],#0x1    ; w10,[src],#1

NSX:0000::FFFFFFDA401C47D4|3800150A_________________________________________________________strb____w10,[x8],#0x1____;_w10,[dest],#1
__NSX:0000::FFFFFFDA401C47D8|35FFFFCA_________________________________________________________cbnz____w10,0xFFFFFFDA401C47D0
                            |
                            |
                            |
                            |
                            |
                            |
                         120|
  NSX:0000::FFFFFFDA401C47DC|910023E0 
                      add     x0,sp,#0x8       ; entry,sp,#8
  NSX:0000::FFFFFFDA401C47E0|AA1503E1 
                      mov     x1,x21
  NSX:0000::FFFFFFDA401C47E4|9400E4ED 
                      bl      0xFFFFFFDA401FDB98   ; 
trace_event_buffer_commit
  NSX:0000::FFFFFFDA401C47E8|F00134C9 
                      adrp    x9,0xFFFFFFDA4285F000
  NSX:0000::FFFFFFDA401C47EC|F85F83A8 
                      ldur    x8,[x29,#-0x8]   ; x8,[x29,#-8]
  NSX:0000::FFFFFFDA401C47F0|F9420929 
                      ldr     x9,[x9,#0x410]   ; x9,[x9,#1040]
  NSX:0000::FFFFFFDA401C47F4|EB08013F 
                      cmp     x9,x8
  NSX:0000::FFFFFFDA401C47F8|54000121 
                      b.ne    0xFFFFFFDA401C481C
  NSX:0000::FFFFFFDA401C47FC|A9494FF4 
                      ldp     x20,x19,[sp,#0x90]   ; 
xdst_cgrp,xtask,[sp,#144]
  NSX:0000::FFFFFFDA401C4800|A94857F6 
                      ldp     x22,x21,[sp,#0x80]   ; x__data,x21,[sp,#128]
  NSX:0000::FFFFFFDA401C4804|A9475FF8 
                      ldp     x24,x23,[sp,#0x70]   ; x24,x23,[sp,#112]
  NSX:0000::FFFFFFDA401C4808|A94667FA 
                      ldp     x26,x25,[sp,#0x60]   ; x26,x25,[sp,#96]
  NSX:0000::FFFFFFDA401C480C|A9456FFC 
                      ldp     x28,x27,[sp,#0x50]   ; x28,x27,[sp,#80]
  NSX:0000::FFFFFFDA401C4810|A9447BFD 
                      ldp     x29,x30,[sp,#0x40]   ; x29,x30,[sp,#64]
  NSX:0000::FFFFFFDA401C4814|910283FF 
                      add     sp,sp,#0xA0      ; sp,sp,#160
  NSX:0000::FFFFFFDA401C4818|D65F03C0 
                      ret
  NSX:0000::FFFFFFDA401C481C|97FC50DC 
                      bl      0xFFFFFFDA400D8B8C   ; __stack_chk_fail

> Note, this code has __string() which does a strlen() which appears to be
> working fine.

 I did see this as well.

 500 #define __string(item, src) __dynamic_array(char, item,         \
 501             strlen((src) ? (const char *)(src) : "(null)") + 1)



My tester reported they could change the task->comm.
for example from "123456789abcde" to "test"
I wonder if we prepare the buffer as "test" 5bytes with __string
then  __assign_str  with "123456789abcde" new task->comm.

but this is very hard race condition.

this is not easy to reproduced, we got 2 instances of this problem.

I read others using the task->comm as trace event with memcpy as this 
patch I initialized.



> >      cgroup_attach_task+0x2e8/0x41c
> >      __cgroup1_procs_write+0x114/0x1ec
> >      cgroup1_tasks_write+0x10/0x18
> >      cgroup_file_write+0xa4/0x208
> >      kernfs_fop_write+0x1f0/0x2f4
> >      __vfs_write+0x5c/0x200
> >      vfs_write+0xe0/0x1a0
> >      ksys_write+0x74/0xdc
> >      __arm64_sys_write+0x18/0x20
> >      el0_svc_common+0xc0/0x1a4
> >      el0_svc_compat_handler+0x18/0x20
> >      el0_svc_compat+0x8/0x2c
>
> Can you give the full debug report, that includes the register content and
> everything else.

here is the crash stack of cpu regs.
you can ref the asm code above.


pc : [0xffffffda401c47d4] trace_event_raw_event_cgroup_migrate+0x124/0x170
lr : [0xffffffda401c4774] trace_event_raw_event_cgroup_migrate+0xc4/0x170
sp : ffffffc01f8e9aa0
x29: ffffffc01f8e9ae0 x28: 000000000000000b
x27: 0000000000000009 x26: ffffffda41f1e515
x25: 0000000000000008 x24: ffffffda42c72a7d
x23: ffffffbd1b6c59d0 x22: ffffffbbf383bec8
x21: 0000000000000034 x20: ffffffbd621cd000
x19: ffffffbd1b6c5140 x18: 0000000000000008
x17: ffffffbd66b96010 x16: ffffffbd621cd000
x15: ffffffbc11583860 x14: ffffffbd1b6c5ba8
x13: 0000000000000000 x12: 0000000000200000
x11: 0000000000000001 x10: 0000000000000000
x9 : ffffffbd1b6c59e0 x8 : ffffffbcf7450000
x7 : 6a716e76225c435a x6 : 0000800000008080
x5 : 0000000000000001 x4 : 0000000000000080
x3 : 0000000000000034 x2 : 0000000000000098
x1 : 0000000000000034 x0 : ffffffbcf744ffc8



> -- Steve