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Message-Id: <201712041944.HAI56745.HOFQFtJSOVMOFL@I-love.SAKURA.ne.jp>
Date: Mon, 4 Dec 2017 19:44:54 +0900
From: Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>
To: james.l.morris@...cle.com
Cc: bot+015afdb01dbf2abb6a6bfdd5430b72e5503fca6d@...kaller.appspotmail.com,
linux-security-module@...r.kernel.org, selinux@...ho.nsa.gov,
syzkaller-bugs@...glegroups.com, danielj@...lanox.com,
dledford@...hat.com, eparis@...isplace.org, junil0814.lee@....com,
kyeongdon.kim@....com, linux-kernel@...r.kernel.org,
mka@...omium.org, paul@...l-moore.com, sds@...ho.nsa.gov,
serge@...lyn.com
Subject: Re: KASAN: slab-out-of-bounds Read in strcmp
James Morris wrote:
> On Sun, 3 Dec 2017, Tetsuo Handa wrote:
>
> > Tetsuo Handa wrote:
> > > which will allow strcmp() to trigger out of bound read when "size" is
> > > larger than strlen(initial_sid_to_string[i]).
> >
> > Oops. "smaller" than.
> >
> > >
> > > Thus, I guess the simplest fix is to use strncmp() instead of strcmp().
> >
> > Can somebody test below patch? (My CentOS 7 environment does not support
> > enabling SELinux in linux.git . Userspace tool is too old to support?)
>
> You mean enabling KASAN? Yep, you need gcc 4.9.2 or better. Recent
> Fedora has it.
I was not able to find "SELinux: Initializing." line for some reason, and
it turned out that I just forgot to run "make install". ;-)
I tested using debug printk() and init for built-in initramfs shown below.
It is strange that KASAN does not trigger upon strcmp()ing
initial_sid_to_string[1]. But anyway, my patch fixes this problem.
----------
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -5973,6 +5973,7 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
PROCESS__SETCURRENT, NULL);
else
error = -EINVAL;
+ printk("setprocattr %s=%d size=%lu\n", name, error, size);
if (error)
return error;
diff --git a/security/selinux/ss/services.c b/security/selinux/ss/services.c
index 33cfe5d..fbf0ade 100644
--- a/security/selinux/ss/services.c
+++ b/security/selinux/ss/services.c
@@ -1417,6 +1417,7 @@ static int security_context_to_sid_core(const char *scontext, u32 scontext_len,
int i;
for (i = 1; i < SECINITSID_NUM; i++) {
+ printk("Comparing with %s\n", initial_sid_to_string[i]);
if (!strcmp(initial_sid_to_string[i], scontext)) {
*sid = i;
return 0;
----------
----------
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mount.h>
#include <unistd.h>
int main(int argc, char *argv[])
{
int fd;
mount("/proc", "/proc", "proc", 0, NULL);
fd = open("/proc/self/attr/current", O_WRONLY);
write(fd, "n", 1);
close(fd);
return 0;
}
----------
----------
[ 7.894061] Write protecting the kernel read-only data: 71680k
[ 7.899889] Freeing unused kernel memory: 1744K
[ 7.923592] Freeing unused kernel memory: 1832K
[ 7.926960] setprocattr current=0 size=1
[ 7.928253] Comparing with kernel
[ 7.929350] Comparing with security
[ 7.930457] Comparing with unlabeled
[ 7.931581] Comparing with fs
[ 7.932538] Comparing with file
[ 7.933537] Comparing with file_labels
[ 7.934720] Comparing with init
[ 7.935719] Comparing with any_socket
[ 7.936866] Comparing with port
[ 7.937874] Comparing with netif
[ 7.938965] ==================================================================
[ 7.941183] BUG: KASAN: slab-out-of-bounds in strcmp+0x96/0xb0
[ 7.942957] Read of size 1 at addr ffff8801145a5441 by task init/1
[ 7.944832]
[ 7.945349] CPU: 2 PID: 1 Comm: init Not tainted 4.15.0-rc2+ #323
[ 7.947177] Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 07/02/2015
[ 7.950331] Call Trace:
[ 7.951133] dump_stack+0x12e/0x188
[ 7.952222] ? vprintk_default+0x28/0x30
[ 7.953431] ? strcmp+0x96/0xb0
[ 7.954421] print_address_description+0x73/0x260
[ 7.955860] ? strcmp+0x96/0xb0
[ 7.956855] kasan_report+0x22b/0x340
[ 7.957987] __asan_report_load1_noabort+0x14/0x20
[ 7.959460] strcmp+0x96/0xb0
[ 7.960408] security_context_to_sid_core+0x312/0x450
[ 7.961945] ? string_to_context_struct+0x940/0x940
[ 7.963434] ? vprintk_func+0x5e/0xc0
[ 7.964564] ? printk+0xaa/0xca
[ 7.965554] ? show_regs_print_info+0x65/0x65
[ 7.966876] ? proc_pid_attr_write+0x169/0x280
[ 7.968178] security_context_to_sid+0x32/0x40
[ 7.969480] selinux_setprocattr+0x2e1/0x8f0
[ 7.970734] ? ptrace_parent_sid+0x400/0x400
[ 7.972034] security_setprocattr+0x85/0xc0
[ 7.973326] proc_pid_attr_write+0x1d8/0x280
[ 7.974638] __vfs_write+0x10d/0x610
[ 7.975746] ? comm_write+0x230/0x230
[ 7.976903] ? kernel_read+0x120/0x120
[ 7.978064] ? __might_sleep+0x95/0x190
[ 7.979266] ? rcu_read_lock_sched_held+0xa3/0x120
[ 7.980722] ? rcu_sync_lockdep_assert+0x70/0xb0
[ 7.982134] ? __sb_start_write+0x211/0x2d0
[ 7.983413] vfs_write+0x18d/0x510
[ 7.984477] SyS_write+0xd4/0x1a0
[ 7.985518] ? SyS_read+0x1a0/0x1a0
[ 7.986622] ? trace_hardirqs_on_caller+0x442/0x5c0
[ 7.988107] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 7.989524] entry_SYSCALL_64_fastpath+0x1f/0x96
[ 7.990928] RIP: 0033:0x40f7a0
[ 7.991875] RSP: 002b:00007ffe20eb59c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 7.994144] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000040f7a0
[ 7.996262] RDX: 0000000000000001 RSI: 0000000000492b75 RDI: 0000000000000003
[ 7.998372] RBP: 00007ffe20eb59a0 R08: 0000000000000000 R09: 0000000000000004
[ 8.000498] R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffe20eb5af8
[ 8.002629] R13: 00007ffe20eb5b08 R14: 0000000000000002 R15: 0000000000000000
[ 8.004774]
[ 8.005283] Allocated by task 1:
[ 8.006283] save_stack+0x46/0xd0
[ 8.007312] kasan_kmalloc+0xad/0xe0
[ 8.008417] __kmalloc_track_caller+0x192/0x760
[ 8.009804] memdup_user+0x2c/0x80
[ 8.010873] proc_pid_attr_write+0x115/0x280
[ 8.012172] __vfs_write+0x10d/0x610
[ 8.013283] vfs_write+0x18d/0x510
[ 8.014336] SyS_write+0xd4/0x1a0
[ 8.015380] entry_SYSCALL_64_fastpath+0x1f/0x96
[ 8.016793]
[ 8.017302] Freed by task 1:
[ 8.018211] save_stack+0x46/0xd0
[ 8.019241] kasan_slab_free+0x71/0xc0
[ 8.020389] kfree+0xca/0x250
[ 8.021317] acpi_ds_create_operand+0x45f/0x664
[ 8.022696] acpi_ds_evaluate_name_path+0x116/0x3b6
[ 8.024165] acpi_ds_exec_end_op+0x291/0xd61
[ 8.025469] acpi_ps_parse_loop+0x1338/0x13ee
[ 8.026815] acpi_ps_parse_aml+0x23a/0x7f4
[ 8.028064] acpi_ps_execute_method+0x4f2/0x55f
[ 8.029451] acpi_ns_evaluate+0x6ba/0x8d3
[ 8.030708] acpi_ut_evaluate_object+0x122/0x3c5
[ 8.032108] acpi_ut_execute_STA+0x84/0x15a
[ 8.033390] acpi_get_object_info+0x431/0x9bd
[ 8.034676] acpi_init_device_object+0xb65/0x15f0
[ 8.036040] acpi_add_single_object+0x119/0x1630
[ 8.037384] acpi_bus_check_add+0x1c7/0x520
[ 8.038656] acpi_ns_walk_namespace+0x1e0/0x346
[ 8.040029] acpi_walk_namespace+0xb5/0xef
[ 8.041277] acpi_bus_scan+0xe0/0xf0
[ 8.042376] acpi_scan_init+0x258/0x5e5
[ 8.043578] acpi_init+0x650/0x6d8
[ 8.044654] do_one_initcall+0x9e/0x2c9
[ 8.045843] kernel_init_freeable+0x476/0x52a
[ 8.047165] kernel_init+0x13/0x172
[ 8.048248] ret_from_fork+0x24/0x30
[ 8.049762]
[ 8.050268] The buggy address belongs to the object at ffff8801145a5440
[ 8.050268] which belongs to the cache kmalloc-32 of size 32
[ 8.053780] The buggy address is located 1 bytes inside of
[ 8.053780] 32-byte region [ffff8801145a5440, ffff8801145a5460)
[ 8.057068] The buggy address belongs to the page:
[ 8.058525] page:00000000243fc1bc count:1 mapcount:0 mapping:000000008e54372e index:0xffff8801145a5fc1
[ 8.061337] flags: 0x2fffc0000000100(slab)
[ 8.062619] raw: 02fffc0000000100 ffff8801145a5000 ffff8801145a5fc1 0000000100000020
[ 8.064922] raw: ffffea0004516ca0 ffff880119c01240 ffff880119c001c0 0000000000000000
[ 8.067232] page dumped because: kasan: bad access detected
[ 8.068902]
[ 8.069409] Memory state around the buggy address:
[ 8.070849] ffff8801145a5300: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
[ 8.073016] ffff8801145a5380: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
[ 8.075194] >ffff8801145a5400: fb fb fb fb fc fc fc fc 01 fc fc fc fc fc fc fc
[ 8.077367] ^
[ 8.078977] ffff8801145a5480: fb fb fb fb fc fc fc fc fb fb fb fb fc fc fc fc
[ 8.081133] ffff8801145a5500: 06 fc fc fc fc fc fc fc fb fb fb fb fc fc fc fc
[ 8.083293] ==================================================================
[ 8.085394] Disabling lock debugging due to kernel taint
[ 8.086963] Comparing with netmsg
[ 8.088029] Comparing with node
[ 8.088992] Comparing with igmp_packet
[ 8.090156] Comparing with icmp_socket
[ 8.091319] Comparing with tcp_socket
[ 8.092447] Comparing with sysctl_modprobe
[ 8.093731] Comparing with sysctl
[ 8.094805] Comparing with sysctl_fs
[ 8.095905] Comparing with sysctl_kernel
[ 8.097113] Comparing with sysctl_net
[ 8.098188] Comparing with sysctl_net_unix
[ 8.099370] Comparing with sysctl_vm
[ 8.100449] Comparing with sysctl_dev
[ 8.101571] Comparing with kmod
[ 8.102525] Comparing with policy
[ 8.103550] Comparing with scmp_packet
[ 8.105942] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000000
----------
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