> -----Original Message----- > From: Darren Hart <dvhart@xxxxxxxxxxxxx> > Sent: Wednesday, April 3, 2019 3:16 PM > To: Steven Rostedt; Limonciello, Mario > Cc: LKML; platform-driver-x86@xxxxxxxxxxxxxxx; Andy Shevchenko; Pali Rohár; Tom > Zanussi > Subject: Re: [PATCH] platform/x86: dell-smbios-base: Fix use after free on failure of > dell_smbios_init() > > > [EXTERNAL EMAIL] > > On Wed, Apr 03, 2019 at 03:20:18PM -0400, Steven Rostedt wrote: > > From: "Steven Rostedt (VMware)" <rostedt@xxxxxxxxxxx> > > > > If da_tokens are allocated, but dell_smbios_init() eventually fails, it will > > free the da_tokens but it does not reset the da_num_tokens number. This > > leads to the possibility of a use after free in dell_smbios_find_token(). > > As da_tokens is not NULL and da_num_tokens is set to something other than 0. > > > > By reseting the da_num_tokens to zero, and da_tokens to NULL after it is > > freed, then access into the other functions that reference them will not > > read freed memory. > > Upon closer inspections this appears to be a race more than an access > issue. Even with this patch, there is still the space between kfree() > and da_num_tokens = 0. This could be addressed by setting da_num_tokens > to 0 prior to the call to kfree(). > > That said, the bigger issue here seems to be the ability to use the > dell_smbios_find_token() call before the module_init() has completed > successfully. > > Mario, care to weigh in? > As I can tell as soon as da_num_tokens is set to 0 that function should be safe to call though even if module_init wasn't finished yet. > > > > This was caught by a KASAN report: > > > > ================================================================== > > BUG: KASAN: use-after-free in dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > Read of size 2 at addr ffff88840c2bc1a8 by task systemd-udevd/479 > > > > CPU: 0 PID: 479 Comm: systemd-udevd Not tainted 5.1.0-rc1+ #9 > > Hardware name: Dell Inc. XPS 13 9360/02PG84, BIOS 2.3.1 10/03/2017 > > Call Trace: > > dump_stack+0x7c/0xbb > > ? dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > print_address_description+0xc7/0x280 > > ? dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > ? dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > kasan_report+0x14e/0x192 > > ? dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > dell_smbios_find_token+0x2e/0x80 [dell_smbios] > > kbd_led_init+0x2e7/0x473 [dell_laptop] > > ? dmi_matched+0x2a/0x2a [dell_laptop] > > ? get_device_parent.isra.28+0x2a0/0x2a0 > > ? lockdep_init_map+0x98/0x2c0 > > ? platform_device_add+0x1b5/0x3a0 > > dell_init+0x4ad/0xb63 [dell_laptop] > > ? kbd_led_init+0x473/0x473 [dell_laptop] > > ? ___slab_alloc+0x61f/0x700 > > ? ___slab_alloc+0x61f/0x700 > > ? preempt_count_sub+0x15/0x100 > > ? kbd_led_init+0x473/0x473 [dell_laptop] > > do_one_initcall+0xbd/0x3fd > > ? perf_trace_initcall_level+0x280/0x280 > > ? kasan_unpoison_shadow+0x30/0x40 > > ? __kasan_kmalloc.constprop.8+0xa0/0xd0 > > ? kmem_cache_alloc_trace+0x163/0x390 > > ? kasan_unpoison_shadow+0x30/0x40 > > do_init_module+0xe3/0x341 > > load_module+0x2fc5/0x3ad0 > > ? layout_and_allocate+0x1170/0x1170 > > ? vfs_read+0xd4/0x1b0 > > ? kernel_read+0x74/0xa0 > > ? kernel_read_file+0x148/0x320 > > ? seccomp_notify_release+0x110/0x110 > > ? __do_sys_finit_module+0x192/0x1c0 > > __do_sys_finit_module+0x192/0x1c0 > > ? __ia32_sys_init_module+0x40/0x40 > > ? syscall_trace_enter+0x184/0x5e0 > > ? mark_held_locks+0x1a/0x90 > > do_syscall_64+0x72/0x220 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > RIP: 0033:0x7fcb4f5f5a49 > > Code: 00 f3 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 > > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff > > 73 01 c3 48 8b 0d 0f b4 2c 00 f7 d8 64 89 01 48 > > RSP: 002b:00007ffc73e340b8 EFLAGS: 00000246 ORIG_RAX: 0000000000000139 > > RAX: ffffffffffffffda RBX: 00005599992bb850 RCX: 00007fcb4f5f5a49 > > RDX: 0000000000000000 RSI: 00007fcb4f2e11c5 RDI: 0000000000000010 > > RBP: 00007fcb4f2e11c5 R08: 0000000000000000 R09: 00005599992bb850 > > R10: 0000000000000010 R11: 0000000000000246 R12: 0000000000000000 > > R13: 0000559999298f40 R14: 0000000000020000 R15: 00005599992bb850 > > > > Allocated by task 479: > > __kasan_kmalloc.constprop.8+0xa0/0xd0 > > krealloc+0xa0/0xc0 > > 0xffffffffc0cc0075 > > dmi_decode_table+0xf6/0x140 > > dmi_walk+0x46/0x70 > > 0xffffffffc0cc0109 > > do_one_initcall+0xbd/0x3fd > > do_init_module+0xe3/0x341 > > load_module+0x2fc5/0x3ad0 > > __do_sys_finit_module+0x192/0x1c0 > > do_syscall_64+0x72/0x220 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > Freed by task 479: > > __kasan_slab_free+0x111/0x150 > > kfree+0xf5/0x350 > > 0xffffffffc0cc01d4 > > do_one_initcall+0xbd/0x3fd > > do_init_module+0xe3/0x341 > > load_module+0x2fc5/0x3ad0 > > __do_sys_finit_module+0x192/0x1c0 > > do_syscall_64+0x72/0x220 > > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > > > The buggy address belongs to the object at ffff88840c2bc1a8 > > which belongs to the cache kmalloc-2k of size 2048 > > The buggy address is located 0 bytes inside of > > 2048-byte region [ffff88840c2bc1a8, ffff88840c2bc9a8) > > The buggy address belongs to the page: > > page:ffffea001030ae00 count:1 mapcount:0 mapping:ffff8884204113c0 > index:0x0 > > compound_mapcount: 0 > > flags: 0x17ffffc0010200(slab|head) > > raw: 0017ffffc0010200 ffffea0010367608 ffffea000ea31808 ffff8884204113c0 > > raw: 0000000000000000 00000000000d000d 00000001ffffffff > 0000000000000000 > > page dumped because: kasan: bad access detected > > > > Memory state around the buggy address: > > ffff88840c2bc080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > > ffff88840c2bc100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > > >ffff88840c2bc180: fc fc fc fc fc fb fb fb fb fb fb fb fb fb fb fb > > ^ > > ffff88840c2bc200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ffff88840c2bc280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > > ================================================================== > > > > Link: http://lkml.kernel.org/r/1553106560.2080.5.camel@xxxxxxxxx > > > > Reported-by: Tom Zanussi <tzanussi@xxxxxxxxx> > > Tested-by: Tom Zanussi <tzanussi@xxxxxxxxx> > > Signed-off-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> > > --- > > drivers/platform/x86/dell-smbios-base.c | 2 ++ > > 1 file changed, 2 insertions(+) > > > > diff --git a/drivers/platform/x86/dell-smbios-base.c b/drivers/platform/x86/dell- > smbios-base.c > > index 0537d44d45a6..a74c0df25b15 100644 > > --- a/drivers/platform/x86/dell-smbios-base.c > > +++ b/drivers/platform/x86/dell-smbios-base.c > > @@ -625,6 +625,8 @@ static int __init dell_smbios_init(void) > > > > fail_platform_driver: > > kfree(da_tokens); > > + da_tokens = NULL; > > + da_num_tokens = 0; > > return ret; > > } > > > > -- > > 2.20.1 > > > > > > -- > Darren Hart > VMware Open Source Technology Center
