security, hugetlbfs: write to user memory in hugetlbfs_destroy_inode

[Dmitry Vyukov]

Hello,

I've got the following report while running syzkaller fuzzer on
093b995e3b55a0ae0670226ddfcb05bfbf0099ae. Note the preceding injected
kmalloc failure in inode_alloc_security, most likely it's the root
cause.


FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 3 PID: 14086 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #364
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x1b8/0x28d lib/dump_stack.c:52
fail_dump lib/fault-inject.c:45 [inline]
should_fail+0x78a/0x870 lib/fault-inject.c:154
should_failslab+0xec/0x120 mm/failslab.c:31
slab_pre_alloc_hook mm/slab.h:434 [inline]
slab_alloc mm/slab.c:3394 [inline]
kmem_cache_alloc+0x200/0x720 mm/slab.c:3570
kmem_cache_zalloc include/linux/slab.h:653 [inline]
inode_alloc_security security/selinux/hooks.c:221 [inline]
selinux_inode_alloc_security+0xf9/0x390 security/selinux/hooks.c:2833
security_inode_alloc+0x90/0xd0 security/security.c:387
inode_init_always+0x5af/0xc20 fs/inode.c:166
alloc_inode+0x82/0x180 fs/inode.c:214
new_inode_pseudo+0x69/0x190 fs/inode.c:889
new_inode+0x1c/0x40 fs/inode.c:918
hugetlbfs_get_inode+0x40/0x420 fs/hugetlbfs/inode.c:734
hugetlb_file_setup+0x329/0x9f0 fs/hugetlbfs/inode.c:1282
newseg+0x422/0xd30 ipc/shm.c:575
ipcget_new ipc/util.c:285 [inline]
ipcget+0x21e/0x580 ipc/util.c:639
SYSC_shmget ipc/shm.c:673 [inline]
SyS_shmget+0x158/0x230 ipc/shm.c:657
entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f9dcc5df858 EFLAGS: 00000282 ORIG_RAX: 000000000000001d
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000000000800 RSI: 0000000000003000 RDI: 0000000000000000
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020207000 R11: 0000000000000282 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f9dcc5df618 R15: 00007f9dcc5df788
==================================================================
BUG: KASAN: user-memory-access in atomic_inc
include/asm-generic/atomic-instrumented.h:87 [inline] at addr
000000131730bd7a
BUG: KASAN: user-memory-access in __lock_acquire+0x21a/0x3a80
kernel/locking/lockdep.c:3239 at addr 000000131730bd7a
Write of size 4 by task syz-executor6/14086
CPU: 3 PID: 14086 Comm: syz-executor6 Not tainted 4.11.0-rc3+ #364
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:16 [inline]
dump_stack+0x1b8/0x28d lib/dump_stack.c:52
kasan_report_error mm/kasan/report.c:291 [inline]
kasan_report.part.2+0x34a/0x480 mm/kasan/report.c:316
kasan_report+0x21/0x30 mm/kasan/report.c:303
check_memory_region_inline mm/kasan/kasan.c:326 [inline]
check_memory_region+0x137/0x190 mm/kasan/kasan.c:333
kasan_check_write+0x14/0x20 mm/kasan/kasan.c:344
atomic_inc include/asm-generic/atomic-instrumented.h:87 [inline]
__lock_acquire+0x21a/0x3a80 kernel/locking/lockdep.c:3239
lock_acquire+0x1ee/0x590 kernel/locking/lockdep.c:3762
__raw_write_lock include/linux/rwlock_api_smp.h:210 [inline]
_raw_write_lock+0x33/0x50 kernel/locking/spinlock.c:295
mpol_free_shared_policy+0x43/0xb0 mm/mempolicy.c:2536
hugetlbfs_destroy_inode+0xca/0x120 fs/hugetlbfs/inode.c:952
alloc_inode+0x10d/0x180 fs/inode.c:216
new_inode_pseudo+0x69/0x190 fs/inode.c:889
new_inode+0x1c/0x40 fs/inode.c:918
hugetlbfs_get_inode+0x40/0x420 fs/hugetlbfs/inode.c:734
hugetlb_file_setup+0x329/0x9f0 fs/hugetlbfs/inode.c:1282
newseg+0x422/0xd30 ipc/shm.c:575
ipcget_new ipc/util.c:285 [inline]
ipcget+0x21e/0x580 ipc/util.c:639
SYSC_shmget ipc/shm.c:673 [inline]
SyS_shmget+0x158/0x230 ipc/shm.c:657
entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f9dcc5df858 EFLAGS: 00000282 ORIG_RAX: 000000000000001d
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000000000800 RSI: 0000000000003000 RDI: 0000000000000000
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000020207000 R11: 0000000000000282 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f9dcc5df618 R15: 00007f9dcc5df788
==================================================================

[Dmitry Vyukov]

Similar on address 0x2d302e31312e35c7, looks like uninit.

==================================================================
BUG: KASAN: wild-memory-access in atomic_inc

include/asm-generic/atomic-instrumented.h:87 [inline] at addr

2d302e31312e35c7
BUG: KASAN: wild-memory-access in __lock_acquire+0x21a/0x3a80
kernel/locking/lockdep.c:3239 at addr 2d302e31312e35c7
Write of size 4 by task syz-executor1/9446
CPU: 1 PID: 9446 Comm: syz-executor1 Not tainted 4.11.0-rc3+ #364

RSP: 002b:00007fc865dbe858 EFLAGS: 00000282 ORIG_RAX: 000000000000001d

RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000000000800 RSI: 0000000000003000 RDI: 0000000000000000
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000

R10: 0000000020002000 R11: 0000000000000282 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007fc865dbe618 R15: 00007fc865dbe788
==================================================================

[Tetsuo Handa]

Dmitry Vyukov wrote:
> On Thu, Mar 23, 2017 at 2:06 PM, Dmitry Vyukov <dvy...@google.com> wrote:
> > Hello,
> >
> > I've got the following report while running syzkaller fuzzer on
> > 093b995e3b55a0ae0670226ddfcb05bfbf0099ae. Note the preceding injected
> > kmalloc failure in inode_alloc_security, most likely it's the root
> > cause.

I don't think inode_alloc_security() failure is the root cause.
I think this is a bug in hugetlbfs or mm part.

If inode_alloc_security() fails, inode->i_security remains NULL
which was initialized to NULL at security_inode_alloc(). Thus,
security_inode_alloc() is irrelevant to this problem.

inode_init_always() returned -ENOMEM due to fault injection and

if (unlikely(inode_init_always(sb, inode))) {
if (inode->i_sb->s_op->destroy_inode)
inode->i_sb->s_op->destroy_inode(inode);
else
kmem_cache_free(inode_cachep, inode);
return NULL;
}

hugetlbfs_destroy_inode() was called via inode->i_sb->s_op->destroy_inode()
when inode initialization failed

static void hugetlbfs_destroy_inode(struct inode *inode)
{
hugetlbfs_inc_free_inodes(HUGETLBFS_SB(inode->i_sb));
mpol_free_shared_policy(&HUGETLBFS_I(inode)->policy);
call_rcu(&inode->i_rcu, hugetlbfs_i_callback);
}

but mpol_shared_policy_init() is called only when new_inode() succeeds.

inode = new_inode(sb);
if (inode) {
(...snipped...)
info = HUGETLBFS_I(inode);
/*
* The policy is initialized here even if we are creating a
* private inode because initialization simply creates an
* an empty rb tree and calls rwlock_init(), later when we
* call mpol_free_shared_policy() it will just return because
* the rb tree will still be empty.
*/
mpol_shared_policy_init(&info->policy, NULL);

[Mike Kravetz]

Thank you for analysis (and Dmitry for reporting).

This certainly does look like a hugetlbfs bug. I will put together a
patch to fix.

--
Mike Kravetz