[PATCH] idr: fix use-after-free in ida_pre_get()

[Dmitry Vyukov]

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@xxxxxxxxxx>
Cc: Matthew Wilcox <mawilcox@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: ross.zwisler@xxxxxxxxxxxxxxx
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: tj@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: syzkaller@xxxxxxxxxxxxxxxx

---

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