Subject: Re: [PATCH v2] proc/sysctl: Fix NULL pointer dereference in put_links

From: Luis Chamberlain <[email-masked]>
Date: Thu, 14 Mar 2019 13:34:37 +0000

On Thu, Mar 14, 2019 at 04:55:27PM +0800, Yue Haibing wrote:
> From: YueHaibing <[email-masked]>
> 
> Syzkaller report this:
> 
> kasan: GPF could be caused by NULL-ptr deref or user memory access
> general protection fault: 0000 [#1] SMP KASAN PTI
> CPU: 1 PID: 5373 Comm: syz-executor.0 Not tainted 5.0.0-rc8+ #3
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
> RIP: 0010:put_links+0x101/0x440 fs/proc/proc_sysctl.c:1599
> Code: 00 0f 85 3a 03 00 00 48 8b 43 38 48 89 44 24 20 48 83 c0 38 48 89 c2 48 89 44 24 28 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 3c 02 00 0f 85 fe 02 00 00 48 8b 74 24 20 48 c7 c7 60 2a 9d 91
> RSP: 0018:ffff8881d828f238 EFLAGS: 00010202
> RAX: dffffc0000000000 RBX: ffff8881e01b1140 RCX: ffffffff8ee98267
> RDX: 0000000000000007 RSI: ffffc90001479000 RDI: ffff8881e01b1178
> RBP: dffffc0000000000 R08: ffffed103ee27259 R09: ffffed103ee27259
> R10: 0000000000000001 R11: ffffed103ee27258 R12: fffffffffffffff4
> R13: 0000000000000006 R14: ffff8881f59838c0 R15: dffffc0000000000
> FS:  00007f072254f700(0000) GS:ffff8881f7100000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007fff8b286668 CR3: 00000001f0542002 CR4: 00000000007606e0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> PKRU: 55555554
> Call Trace:
>  drop_sysctl_table+0x152/0x9f0 fs/proc/proc_sysctl.c:1629
>  get_subdir fs/proc/proc_sysctl.c:1022 [inline]
>  __register_sysctl_table+0xd65/0x1090 fs/proc/proc_sysctl.c:1335
>  ? 0xffffffffc1a18000
>  br_netfilter_init+0xbc/0x1000 [br_netfilter]
>  ? 0xffffffffc1a18000
>  ? 0xffffffffc1a18000
>  do_one_initcall+0xfa/0x5ca init/main.c:887
>  do_init_module+0x204/0x5f6 kernel/module.c:3460
>  load_module+0x66b2/0x8570 kernel/module.c:3808
>  __do_sys_finit_module+0x238/0x2a0 kernel/module.c:3902
>  do_syscall_64+0x147/0x600 arch/x86/entry/common.c:290
>  entry_SYSCALL_64_after_hwframe+0x49/0xbe
> RIP: 0033:0x462e99
> Code: f7 d8 64 89 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 bc ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007f072254ec58 EFLAGS: 00000246 ORIG_RAX: 0000000000000139
> RAX: ffffffffffffffda RBX: 000000000073bf00 RCX: 0000000000462e99
> RDX: 0000000000000000 RSI: 0000000020000280 RDI: 0000000000000003
> RBP: 00007f072254ec70 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 00007f072254f6bc
> R13: 00000000004bcefa R14: 00000000006f6fb0 R15: 0000000000000004
> Modules linked in: br_netfilter(+) dvb_usb_dibusb_mc_common dib3000mc dibx000_common dvb_usb_dibusb_common dvb_usb_dw2102 dvb_usb classmate_laptop palmas_regulator cn videobuf2_v4l2 v4l2_common snd_soc_bd28623 mptbase snd_usb_usx2y snd_usbmidi_lib snd_rawmidi wmi libnvdimm lockd sunrpc grace rc_kworld_pc150u rc_core rtc_da9063 sha1_ssse3 i2c_cros_ec_tunnel adxl34x_spi adxl34x nfnetlink lib80211 i5500_temp dvb_as102 dvb_core videobuf2_common videodev media videobuf2_vmalloc videobuf2_memops udc_core lnbp22 leds_lp3952 hid_roccat_ryos s1d13xxxfb mtd vport_geneve openvswitch nf_conncount nf_nat_ipv6 nsh geneve udp_tunnel ip6_udp_tunnel snd_soc_mt6351 sis_agp phylink snd_soc_adau1761_spi snd_soc_adau1761 snd_soc_adau17x1 snd_soc_core snd_pcm_dmaengine ac97_bus snd_compress snd_soc_adau_utils snd_soc_sigmadsp_regmap snd_soc_sigmadsp raid_class hid_roccat_konepure hid_roccat_common hid_roccat c2port_duramar2150 core mdio_bcm_unimac iptable_security iptable_raw iptable_mangle
>  iptable_nat nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_filter bpfilter ip6_vti ip_vti ip_gre ipip sit tunnel4 ip_tunnel hsr veth netdevsim devlink vxcan batman_adv cfg80211 rfkill chnl_net caif nlmon dummy team bonding vcan bridge stp llc ip6_gre gre ip6_tunnel tunnel6 tun crct10dif_pclmul crc32_pclmul crc32c_intel ghash_clmulni_intel joydev mousedev ide_pci_generic piix aesni_intel aes_x86_64 ide_core crypto_simd atkbd cryptd glue_helper serio_raw ata_generic pata_acpi i2c_piix4 floppy sch_fq_codel ip_tables x_tables ipv6 [last unloaded: lm73]
> Dumping ftrace buffer:
>    (ftrace buffer empty)
> ---[ end trace 770020de38961fd0 ]---
> 
> A new dir entry can be created in get_subdir and its 'header->parent' is set
> to NULL. Only after insert_header success, it will be set to 'dir', otherwise
> 'header->parent' is set to NULL and drop_sysctl_table is called. However in err
> handling path of get_subdir, drop_sysctl_table also be called on 'new->header'
> regardless its value of parent pointer. Then put_links is called, which triggers
> NULL-ptr deref when access member of header->parent.
> 
> In fact we have multiple error paths which call drop_sysctl_table() there,
> upon failure on insert_links() we also call drop_sysctl_table().And even in
> the successful case on __register_sysctl_table() we still always
> call drop_sysctl_table().This patch fix it.
> 
> Reported-by: Hulk Robot <[email-masked]>
> Fixes: 0e47c99d7fe25 ("sysctl: Replace root_list with links between sysctl_table_sets")
> Signed-off-by: YueHaibing <[email-masked]>

Acked-by: Luis Chamberlain <[email-masked]>

This should also have:

 Cc: <[email-masked]>    [>= 3.4]

   Luis

> ---
> v2: fix commit log
> ---
>  fs/proc/proc_sysctl.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index 4d598a3..4c2a05a 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -1626,7 +1626,8 @@ static void drop_sysctl_table(struct ctl_table_header *header)
>  	if (--header->nreg)
>  		return;
>  
> -	put_links(header);
> +	if (parent)
> +		put_links(header);
>  	start_unregistering(header);
>  	if (!--header->count)
>  		kfree_rcu(header, rcu);
> -- 
> 2.7.0
> 
>