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Subject[PATCH] idr: fix use-after-free in ida_pre_get()
Date
ida_pre_get() contains a window between checking and installing a new
ida_bitmap in which another task can install own bitmap. The handling
of this race is currently handled incorrectly, we both free the
installed bitmap and leak the new one.

Handle the race correctly.

Signed-off-by: Dmitry Vyukov <dvyukov@google.com>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: ross.zwisler@linux.intel.com
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jan Kara <jack@suse.cz>
Cc: tj@kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: syzkaller@googlegroups.com

---

Found by syzkaller+KASAN as:

==================================================================
BUG: KASAN: use-after-free in ida_get_new_above+0x564/0x9b0
lib/idr.c:295 at addr ffff880160ef3600
Write of size 128 by task syz-executor1/1757
CPU: 1 PID: 1757 Comm: syz-executor1 Not tainted 4.10.0+ #98
Hardware name: Google Google Compute Engine/Google Compute Engine,
BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:15 [inline]
dump_stack+0x2ee/0x3ef lib/dump_stack.c:51
kasan_object_err+0x1c/0x70 mm/kasan/report.c:162
print_address_description mm/kasan/report.c:200 [inline]
kasan_report_error mm/kasan/report.c:289 [inline]
kasan_report.part.2+0x1e5/0x4b0 mm/kasan/report.c:311
kasan_report+0x21/0x30 mm/kasan/report.c:298
check_memory_region_inline mm/kasan/kasan.c:315 [inline]
check_memory_region+0x139/0x190 mm/kasan/kasan.c:322
memset+0x23/0x40 mm/kasan/kasan.c:340
ida_get_new_above+0x564/0x9b0 lib/idr.c:295
ida_get_new include/linux/idr.h:209 [inline]
proc_alloc_inum+0x97/0x1f0 fs/proc/generic.c:201
proc_register+0x25/0x2f0 fs/proc/generic.c:338
proc_create_data+0x100/0x190 fs/proc/generic.c:509
proc_create include/linux/proc_fs.h:35 [inline]
ip_rt_do_proc_init+0x53/0x110 net/ipv4/route.c:382
ops_init+0x10a/0x530 net/core/net_namespace.c:115
setup_net+0x2ed/0x690 net/core/net_namespace.c:291
copy_net_ns+0x26c/0x530 net/core/net_namespace.c:396
create_new_namespaces+0x409/0x860 kernel/nsproxy.c:106
unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:205
SYSC_unshare kernel/fork.c:2281 [inline]
SyS_unshare+0x64e/0xfc0 kernel/fork.c:2231
entry_SYSCALL_64_fastpath+0x1f/0xc2
RIP: 0033:0x44fb79
RSP: 002b:00007f1b66930b58 EFLAGS: 00000212 ORIG_RAX: 0000000000000110
RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 000000000044fb79
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000062020200
RBP: 0000000062020200 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000212 R12: 00000000007082a0
R13: 0000000000000004 R14: 0000000000000400 R15: 0000000000000000
Object at ffff880160ef3600, in cache kmalloc-128 size: 128
Allocated:
PID = 1730
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:502
set_track mm/kasan/kasan.c:514 [inline]
kasan_kmalloc+0xaa/0xd0 mm/kasan/kasan.c:605
kmem_cache_alloc_trace+0x10b/0x670 mm/slab.c:3634
kmalloc include/linux/slab.h:490 [inline]
ida_pre_get+0xcd/0xe0 lib/radix-tree.c:2129
proc_alloc_inum+0xc5/0x1f0 fs/proc/generic.c:197
proc_register+0x25/0x2f0 fs/proc/generic.c:338
proc_create_data+0x100/0x190 fs/proc/generic.c:509
proc_create include/linux/proc_fs.h:35 [inline]
packet_net_init+0x8d/0xb0 net/packet/af_packet.c:4488
ops_init+0x10a/0x530 net/core/net_namespace.c:115
setup_net+0x2ed/0x690 net/core/net_namespace.c:291
copy_net_ns+0x26c/0x530 net/core/net_namespace.c:396
create_new_namespaces+0x409/0x860 kernel/nsproxy.c:106
unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:205
SYSC_unshare kernel/fork.c:2281 [inline]
SyS_unshare+0x64e/0xfc0 kernel/fork.c:2231
entry_SYSCALL_64_fastpath+0x1f/0xc2
Freed:
PID = 1648
save_stack_trace+0x16/0x20 arch/x86/kernel/stacktrace.c:57
save_stack+0x43/0xd0 mm/kasan/kasan.c:502
set_track mm/kasan/kasan.c:514 [inline]
kasan_slab_free+0x6f/0xb0 mm/kasan/kasan.c:578
__cache_free mm/slab.c:3510 [inline]
kfree+0xd3/0x250 mm/slab.c:3827
ida_pre_get+0x8a/0xe0 lib/radix-tree.c:2133
ida_simple_get+0x168/0x320 lib/idr.c:443
__kernfs_new_node+0xfe/0x3c0 fs/kernfs/dir.c:633
kernfs_new_node+0x80/0xe0 fs/kernfs/dir.c:661
kernfs_create_dir_ns+0x41/0x140 fs/kernfs/dir.c:933
kernfs_create_dir include/linux/kernfs.h:477 [inline]
internal_create_group+0xf7/0x8f0 fs/sysfs/group.c:124
sysfs_create_group fs/sysfs/group.c:156 [inline]
sysfs_create_groups+0x97/0x130 fs/sysfs/group.c:183
device_add_groups drivers/base/core.c:1031 [inline]
device_add_attrs drivers/base/core.c:1058 [inline]
device_add+0xb2f/0x1650 drivers/base/core.c:1679
netdev_register_kobject+0x183/0x360 net/core/net-sysfs.c:1603
register_netdevice+0xa27/0xed0 net/core/dev.c:7228
tun_set_iff drivers/net/tun.c:1843 [inline]
__tun_chr_ioctl+0x1bd0/0x3b70 drivers/net/tun.c:2046
tun_chr_ioctl+0x2a/0x40 drivers/net/tun.c:2291
vfs_ioctl fs/ioctl.c:43 [inline]
do_vfs_ioctl+0x1bf/0x1790 fs/ioctl.c:683
SYSC_ioctl fs/ioctl.c:698 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:689
entry_SYSCALL_64_fastpath+0x1f/0xc2
Memory state around the buggy address:
ffff880160ef3500: fc fc fc fc fc fc fc fc fb fb fb fb fb fb fb fb
ffff880160ef3580: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff880160ef3600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff880160ef3680: fc fc fc fc fc fc fc fc 00 00 00 00 00 00 00 00
ffff880160ef3700: 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc fc
==================================================================
---
lib/radix-tree.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 5ed506d648c4..691a9ad48497 100644
--- a/lib/radix-tree.c
+++ b/lib/radix-tree.c
@@ -2129,8 +2129,8 @@ int ida_pre_get(struct ida *ida, gfp_t gfp)
struct ida_bitmap *bitmap = kmalloc(sizeof(*bitmap), gfp);
if (!bitmap)
return 0;
- bitmap = this_cpu_cmpxchg(ida_bitmap, NULL, bitmap);
- kfree(bitmap);
+ if (this_cpu_cmpxchg(ida_bitmap, NULL, bitmap))
+ kfree(bitmap);
}

return 1;
--
2.12.0.rc1.440.g5b76565f74-goog
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