idr: use-after-free write in ida_get_new_above

[Dmitry Vyukov <dvyukov@google.com>]

Hello,

I am hitting the following use-after-free reports while running
syzkaller fuzzer on commit c82be9d2244aacea9851c86f4fb74694c99cd874:

==================================================================
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
==================================================================


I think we need:

diff --git a/lib/radix-tree.c b/lib/radix-tree.c
index 5ed506d648c4..d435916f6527 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);
        }


Otherwise we both free the still installed old pointer and leak the new one.