Re: [PATCH v3 1/2] printk: Fix panic caused by passing log_buf_len to command line

[Steven Rostedt]

On Sun, 23 Sep 2018 14:51:12 +0800
He Zhe <zhe.he@xxxxxxxxxxxxx> wrote:

> On 2018å09æ23æ 00:19, Steven Rostedt wrote:
> > On Sat, 22 Sep 2018 23:40:51 +0800
> > <zhe.he@xxxxxxxxxxxxx> wrote:
> >  
> >> From: He Zhe <zhe.he@xxxxxxxxxxxxx>
> >>
> >> log_buf_len_setup does not check input argument before passing it to
> >> simple_strtoull. The argument would be a NULL pointer if "log_buf_len",
> >> without its value, is set in command line and thus causes the following
> >> panic.
> >>
> >> PANIC: early exception 0xe3 IP 10:ffffffffaaeacd0d error 0 cr2 0x0
> >> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc4-yocto-standard+ #1
> >> [    0.000000] RIP: 0010:_parse_integer_fixup_radix+0xd/0x70
> >> ...
> >> [    0.000000] Call Trace:
> >> [    0.000000]  simple_strtoull+0x29/0x70
> >> [    0.000000]  memparse+0x26/0x90
> >> [    0.000000]  log_buf_len_setup+0x17/0x22
> >> [    0.000000]  do_early_param+0x57/0x8e
> >> [    0.000000]  parse_args+0x208/0x320
> >> [    0.000000]  ? rdinit_setup+0x30/0x30
> >> [    0.000000]  parse_early_options+0x29/0x2d
> >> [    0.000000]  ? rdinit_setup+0x30/0x30
> >> [    0.000000]  parse_early_param+0x36/0x4d
> >> [    0.000000]  setup_arch+0x336/0x99e
> >> [    0.000000]  start_kernel+0x6f/0x4ee
> >> [    0.000000]  x86_64_start_reservations+0x24/0x26
> >> [    0.000000]  x86_64_start_kernel+0x6f/0x72
> >> [    0.000000]  secondary_startup_64+0xa4/0xb0
> >>
> >> This patch adds a check to prevent the panic.
> >>
> >> Signed-off-by: He Zhe <zhe.he@xxxxxxxxxxxxx>
> >> Cc: stable@xxxxxxxxxxxxxxx  
> > I just tried this on a 2.6.32 kernel, and it crashes there. I guess
> > this goes farther back than git history goes.
> >
> > Perhaps it should be commented that this bug has been here since
> > creation of (git) time.  
> 
> I did a try on 2.6.32. It passed. Actually this bug only happens on
> early_param(not __setup) which is introduced since v3.0. The oldest

Really? This is what I got:

Linux version 2.6.32-565.el6.x86_64 (mockbuild@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-16) (GCC) ) #1 SMP Tue Jun 2 14:53:05 EDT 2015
Command line: ro root=UUID=b6bbd80c-a321-4350-9d87-ba8ec1f45917 LANG=en_US.UTF-8 SYSFONT=latarcyrheb-sun16 KEYTABLE=us console=ttyS0,115200 crashkernel=auto selinux=0 earlyprintk=ttyS0,115200 log_buf_len
KERNEL supported cpus:
  Intel GenuineIntel
  AMD AuthenticAMD
  Centaur CentaurHauls
BIOS-provided physical RAM map:
 BIOS-e820: 0000000000000000 - 000000000009d800 (usable)
 BIOS-e820: 000000000009d800 - 00000000000a0000 (reserved)
 BIOS-e820: 00000000000e0000 - 0000000000100000 (reserved)
 BIOS-e820: 0000000000100000 - 00000000c69ee000 (usable)
 BIOS-e820: 00000000c69ee000 - 00000000c69f5000 (ACPI NVS)
 BIOS-e820: 00000000c69f5000 - 00000000c6e38000 (usable)
 BIOS-e820: 00000000c6e38000 - 00000000c73c9000 (reserved)
 BIOS-e820: 00000000c73c9000 - 00000000d8dac000 (usable)
 BIOS-e820: 00000000d8dac000 - 00000000d8e44000 (reserved)
 BIOS-e820: 00000000d8e44000 - 00000000d8e95000 (usable)
 BIOS-e820: 00000000d8e95000 - 00000000d8fc8000 (ACPI NVS)
 BIOS-e820: 00000000d8fc8000 - 00000000d9fff000 (reserved)
 BIOS-e820: 00000000d9fff000 - 00000000da000000 (usable)
 BIOS-e820: 00000000db000000 - 00000000df200000 (reserved)
 BIOS-e820: 00000000f8000000 - 00000000fc000000 (reserved)
 BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved)
 BIOS-e820: 00000000fed00000 - 00000000fed04000 (reserved)
 BIOS-e820: 00000000fed1c000 - 00000000fed20000 (reserved)
 BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved)
 BIOS-e820: 00000000ff000000 - 0000000100000000 (reserved)
 BIOS-e820: 0000000100000000 - 000000021ee00000 (usable)
bootconsole [earlyser0] enabled
PANIC: early exception 0e rip 10:ffffffff812a1a4d error 0 cr2 0
Pid: 0, comm: swapper Not tainted 2.6.32-565.el6.x86_64 #1
Call Trace:
 [<ffffffff81043069>] ? native_read_cr2+0x9/0x10
 [<ffffffff81c3719e>] ? early_idt_handler+0x5e/0x71
 [<ffffffff812a1a4d>] ? _parse_integer_fixup_radix+0xd/0x70
 [<ffffffff8129b29a>] ? simple_strtoull+0x1a/0x50
 [<ffffffff8128fde7>] ? memparse+0x17/0x90
 [<ffffffff81c58166>] ? log_buf_len_setup+0x15/0x47
 [<ffffffff81c37790>] ? do_early_param+0x5d/0x89
 [<ffffffff8109dcc7>] ? parse_args+0x197/0x340
 [<ffffffff81c37733>] ? do_early_param+0x0/0x89
 [<ffffffff81c377da>] ? parse_early_options+0x1e/0x20
 [<ffffffff81c37cf2>] ? parse_early_param+0x31/0x3d
 [<ffffffff81c3d548>] ? setup_arch+0x36f/0xc69
 [<ffffffff8153783d>] ? printk+0x41/0x44
 [<ffffffff81c37dda>] ? start_kernel+0xdc/0x431
 [<ffffffff81c3733a>] ? x86_64_start_reservations+0x125/0x129
 [<ffffffff81c37453>] ? x86_64_start_kernel+0x115/0x124
RIP _parse_integer_fixup_radix+0xd/0x70

> LTS version is 3.16 now. Should I send v4 and add a statement about
> the supported version range in commit log?

Fixes tags and stable info can be added by the maintainer that pulls in
the patch. I was just commenting on it for them.

> 
> >
> >  
> >> Cc: pmladek@xxxxxxxx
> >> Cc: sergey.senozhatsky@xxxxxxxxx
> >> Cc: rostedt@xxxxxxxxxxx
> >> ---
> >> v2:
> >> Split out the addition of pr_fmt and the unsigned update  
> > Which unsigned update? As it does switch to unsigned to "unsigned int",
> > but that change is fine to me with this.  
> 
> No problem. It's the history of v2.
> 
> In v1 you suggested "unsigned int size" should be in a separate patch and
> I did that in v2. Then Sergey suggested "unsigned int size" should be in the
> 1/2 patch to avoid checkpatch.pl warning. With your conformation, I add it
> back here in v3.
> 

Yeah, I'm fine with the addition. It should still be stated in the
main change log. The version history is cut from git commits.

Thanks!

-- Steve