net/kcm: double free of kcm inode

[Dmitry Vyukov]

Hello,

I've got the following report while running syzkaller fuzzer. Note the
preceding kmem_cache_alloc injected failure, it's most likely the root
cause.

FAULT_INJECTION: forcing a failure.
name failslab, interval 1, probability 0, space 0, times 0
CPU: 1 PID: 21839 Comm: syz-executor4 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
sk_prot_alloc+0x65/0x2a0 net/core/sock.c:1331
sk_alloc+0x8c/0x710 net/core/sock.c:1393
kcm_clone net/kcm/kcmsock.c:1655 [inline]
kcm_ioctl+0xb65/0x17e0 net/kcm/kcmsock.c:1713
sock_do_ioctl+0x65/0xb0 net/socket.c:895
sock_ioctl+0x2c2/0x440 net/socket.c:993
vfs_ioctl fs/ioctl.c:45 [inline]
do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
SYSC_ioctl fs/ioctl.c:700 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f05eb28e858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000020001000 RSI: 00000000000089e2 RDI: 0000000000000005
RBP: 0000000000000086 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000004a7e31
R13: 0000000000000000 R14: 00007f05eb28e618 R15: 00007f05eb28e788
==================================================================
BUG: KASAN: use-after-free in __fput+0x6b0/0x7f0 fs/file_table.c:211
at addr ffff880037a25670
Read of size 2 by task syz-executor4/21839
CPU: 1 PID: 21839 Comm: syz-executor4 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_object_err+0x1c/0x70 mm/kasan/report.c:166
print_address_description mm/kasan/report.c:210 [inline]
kasan_report_error mm/kasan/report.c:294 [inline]
kasan_report.part.2+0x1be/0x480 mm/kasan/report.c:316
kasan_report mm/kasan/report.c:335 [inline]
__asan_report_load2_noabort+0x29/0x30 mm/kasan/report.c:335
__fput+0x6b0/0x7f0 fs/file_table.c:211
____fput+0x15/0x20 fs/file_table.c:245
task_work_run+0x1a4/0x270 kernel/task_work.c:116
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
entry_SYSCALL_64_fastpath+0xc0/0xc2
RIP: 0033:0x445b79
RSP: 002b:00007f05eb28e858 EFLAGS: 00000286 ORIG_RAX: 0000000000000010
RAX: fffffffffffffff4 RBX: 0000000000708000 RCX: 0000000000445b79
RDX: 0000000020001000 RSI: 00000000000089e2 RDI: 0000000000000005
RBP: 0000000000002170 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000286 R12: 00000000006e0230
R13: 00000000000089e2 R14: 0000000020001000 R15: 0000000000000005
Object at ffff880037a25640, in cache sock_inode_cache size: 944
Allocated:
PID = 21839
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:517
set_track mm/kasan/kasan.c:529 [inline]
kasan_kmalloc+0xbc/0xf0 mm/kasan/kasan.c:620
kasan_slab_alloc+0x12/0x20 mm/kasan/kasan.c:559
kmem_cache_alloc+0x110/0x720 mm/slab.c:3572
sock_alloc_inode+0x70/0x300 net/socket.c:250
alloc_inode+0x65/0x180 fs/inode.c:207
new_inode_pseudo+0x69/0x190 fs/inode.c:889
sock_alloc+0x41/0x270 net/socket.c:565
kcm_clone net/kcm/kcmsock.c:1634 [inline]
kcm_ioctl+0x990/0x17e0 net/kcm/kcmsock.c:1713
sock_do_ioctl+0x65/0xb0 net/socket.c:895
sock_ioctl+0x2c2/0x440 net/socket.c:993
vfs_ioctl fs/ioctl.c:45 [inline]
do_vfs_ioctl+0x1af/0x16d0 fs/ioctl.c:685
SYSC_ioctl fs/ioctl.c:700 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
entry_SYSCALL_64_fastpath+0x1f/0xc2
Freed:
PID = 21839
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:59
save_stack+0x43/0xd0 mm/kasan/kasan.c:517
set_track mm/kasan/kasan.c:529 [inline]
kasan_slab_free+0x81/0xc0 mm/kasan/kasan.c:593
__cache_free mm/slab.c:3514 [inline]
kmem_cache_free+0x71/0x240 mm/slab.c:3774
sock_destroy_inode+0x56/0x70 net/socket.c:280
destroy_inode+0x15d/0x200 fs/inode.c:264
evict+0x57e/0x920 fs/inode.c:570
iput_final fs/inode.c:1515 [inline]
iput+0x62b/0xa20 fs/inode.c:1542
sock_release+0x168/0x1e0 net/socket.c:607
sock_close+0x16/0x20 net/socket.c:1061
__fput+0x327/0x7f0 fs/file_table.c:209
____fput+0x15/0x20 fs/file_table.c:245
task_work_run+0x1a4/0x270 kernel/task_work.c:116
tracehook_notify_resume include/linux/tracehook.h:191 [inline]
exit_to_usermode_loop+0x24d/0x2d0 arch/x86/entry/common.c:161
prepare_exit_to_usermode arch/x86/entry/common.c:191 [inline]
syscall_return_slowpath+0x3bd/0x460 arch/x86/entry/common.c:260
entry_SYSCALL_64_fastpath+0xc0/0xc2
Memory state around the buggy address:
ffff880037a25500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff880037a25580: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fc fc
>ffff880037a25600: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
^
ffff880037a25680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff880037a25700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

On commit 093b995e3b55a0ae0670226ddfcb05bfbf0099ae

[Cong Wang]

I don't know if this patch could fix this bug or not:
https://patchwork.ozlabs.org/patch/742860/

This is why I don't add your Reported-by. But it could be related.

Thanks.

[Dmitry Vyukov]

That patch only handles copy_from_user failures in kcm_ioctl. This
issue is kmem_cache_alloc failure in sk_alloc called from kcm_clone.
I would expect that the patch does not fix it.