WARNING in __check_heap_object

[syzbot]

Hello,

syzkaller hit the following crash on
5a3517e009e979f21977d362212b7729c5165d92
git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
compiler: gcc (GCC) 7.1.1 20170620
.config is attached
Raw console output is attached.
C reproducer is attached
syzkaller reproducer is attached. See https://goo.gl/kgGztJ
for information about syzkaller reproducers


------------[ cut here ]------------
WARNING: CPU: 1 PID: 2994 at mm/slab.c:4434 __check_heap_object+0xbc/0xd0
mm/slab.c:4433
Kernel panic - not syncing: panic_on_warn set ...

CPU: 1 PID: 2994 Comm: syzkaller408738 Not tainted
4.14.0-rc7-next-20171103+ #38
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:17 [inline]
dump_stack+0x194/0x257 lib/dump_stack.c:53
panic+0x1e4/0x41c kernel/panic.c:183
__warn+0x1c4/0x1e0 kernel/panic.c:546
report_bug+0x211/0x2d0 lib/bug.c:184
fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:177
do_trap_no_signal arch/x86/kernel/traps.c:211 [inline]
do_trap+0x260/0x390 arch/x86/kernel/traps.c:260
do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:297
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:310
invalid_op+0x18/0x20 arch/x86/entry/entry_64.S:906
RIP: 0010:__check_heap_object+0xbc/0xd0 mm/slab.c:4433
RSP: 0018:ffff8801ce0670d8 EFLAGS: 00010282
RAX: 000000000000004a RBX: 0000000000000000 RCX: 0000000000000000
RDX: 000000000000004a RSI: 1ffff10039c0cddb RDI: ffffed0039c0ce0f
RBP: ffff8801ce0670e0 R08: 0000000000000001 R09: 0000000000000000
R10: ffff8801ceb0a500 R11: 0000000000000000 R12: ffffea00074a6c80
R13: ffff8801d29b26b0 R14: 000000000000000b R15: ffffea00074a6c80
check_heap_object mm/usercopy.c:222 [inline]
__check_object_size+0x22c/0x4f0 mm/usercopy.c:248
check_object_size include/linux/thread_info.h:112 [inline]
check_copy_size include/linux/thread_info.h:143 [inline]
copy_to_user include/linux/uaccess.h:154 [inline]
sctp_getsockopt_events net/sctp/socket.c:4972 [inline]
sctp_getsockopt+0x2b90/0x70b0 net/sctp/socket.c:7012
sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2924
SYSC_getsockopt net/socket.c:1882 [inline]
SyS_getsockopt+0x178/0x340 net/socket.c:1864
entry_SYSCALL_64_fastpath+0x1f/0xbe
RIP: 0033:0x43fca9
RSP: 002b:00007fff12a2dfa8 EFLAGS: 00000203 ORIG_RAX: 0000000000000037
RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 000000000043fca9
RDX: 000000000000000b RSI: 0000000000000084 RDI: 0000000000000003
RBP: 0000000000000086 R08: 0000000020290000 R09: 0000000000000000
R10: 000000002099aff5 R11: 0000000000000203 R12: 0000000000401610
R13: 00000000004016a0 R14: 0000000000000000 R15: 0000000000000000
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


---
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[Christopher Lameter]

Well that is a security thingamy related to CONFIG_HARDDENED_USERCOPY.
Kees?


----- Offending function

#ifdef CONFIG_HARDENED_USERCOPY
/*
* Rejects objects that are incorrectly sized.
*
* Returns NULL if check passes, otherwise const char * to name of cache
* to indicate an error.
*/
const char *__check_heap_object(const void *ptr, unsigned long n,
struct page *page)
{
struct kmem_cache *cachep;
unsigned int objnr;
unsigned long offset;

/* Find and validate object. */
cachep = page->slab_cache;
objnr = obj_to_index(cachep, page, (void *)ptr);
BUG_ON(objnr >= cachep->num);

/* Find offset within object. */
offset = ptr - index_to_obj(cachep, page, objnr) -
obj_offset(cachep);

/* Allow address range falling entirely within object size. */
if (offset <= cachep->object_size && n <= cachep->object_size -
offset)
return NULL;

return cachep->name;
}
#endif /* CONFIG_HARDENED_USERCOPY */

[Kees Cook]

On Tue, Nov 7, 2017 at 10:36 AM, syzbot
<bot+2357afb48acb76780f...@syzkaller.appspotmail.com>
wrote:

> Hello,
>
> syzkaller hit the following crash on
> 5a3517e009e979f21977d362212b7729c5165d92
> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
> compiler: gcc (GCC) 7.1.1 20170620
> .config is attached
> Raw console output is attached.
> C reproducer is attached
> syzkaller reproducer is attached. See https://goo.gl/kgGztJ
> for information about syzkaller reproducers
>
>

Please include the line _before_ the "cut here" (dumb, I know, but
that's where warnings show up...)

Found in the raw.log:

[ 44.227177] unexpected usercopy without slab whitelist from SCTPv6
offset 1648 size 11

This means some part of the SCTPv6 slab was being poked into userspace
without a usercopy whitelist.

> check_heap_object mm/usercopy.c:222 [inline]
> __check_object_size+0x22c/0x4f0 mm/usercopy.c:248
> check_object_size include/linux/thread_info.h:112 [inline]
> check_copy_size include/linux/thread_info.h:143 [inline]
> copy_to_user include/linux/uaccess.h:154 [inline]
> sctp_getsockopt_events net/sctp/socket.c:4972 [inline]
> sctp_getsockopt+0x2b90/0x70b0 net/sctp/socket.c:7012
> sock_common_getsockopt+0x95/0xd0 net/core/sock.c:2924
> SYSC_getsockopt net/socket.c:1882 [inline]
> SyS_getsockopt+0x178/0x340 net/socket.c:1864
> entry_SYSCALL_64_fastpath+0x1f/0xbe

Looking at the SCTPv6 slab declaration, it seems David and I missed
the usercopy whitelist for the sctpv6_sock struct. I'll update the
usercopy whitelist patch with:

#syz fix: sctp: Define usercopy region in SCTP proto slab cache

diff --git a/net/sctp/socket.c b/net/sctp/socket.c
index 5fd83974c5cc..8ac85877c0e4 100644
--- a/net/sctp/socket.c
+++ b/net/sctp/socket.c
@@ -8492,6 +8492,10 @@ struct proto sctpv6_prot = {
.unhash = sctp_unhash,
.get_port = sctp_get_port,
.obj_size = sizeof(struct sctp6_sock),
+ .useroffset = offsetof(struct sctp_sock, subscribe),
+ .usersize = offsetof(struct sctp_sock, initmsg) -
+ offsetof(struct sctp_sock, subscribe) +
+ sizeof_field(struct sctp_sock, initmsg),
.sysctl_mem = sysctl_sctp_mem,
.sysctl_rmem = sysctl_sctp_rmem,
.sysctl_wmem = sysctl_sctp_wmem,

Thanks!

-Kees

--
Kees Cook
Pixel Security

[Dmitry Vyukov]

Kees, please also follow this part once the commit reaches any of
trees (title is settled):

> syzbot will keep track of this bug report.
> Once a fix for this bug is committed, please reply to this email with:
> #syz fix: exact-commit-title

> Note: all commands must start from beginning of the line.

This will greatly help to keep the whole process running and report
new bugs in future.

Thanks

[Kees Cook]

I included that in my email reply already, and the commit will be in
-next shortly. (Do you prefer something else?)

[Dmitry Vyukov]

Doh! That's just me trying to handle 200 bugs at the same time. Sorry.