CVE-2021-47146 in Linux
Summary
by MITRE • 03/25/2024
In the Linux kernel, the following vulnerability has been resolved:
mld: fix panic in mld_newpack()
mld_newpack() doesn't allow to allocate high order page, only order-0 allocation is allowed. If headroom size is too large, a kernel panic could occur in skb_put().
Test commands: ip netns del A ip netns del B ip netns add A ip netns add B ip link add veth0 type veth peer name veth1 ip link set veth0 netns A ip link set veth1 netns B
ip netns exec A ip link set lo up ip netns exec A ip link set veth0 up ip netns exec A ip -6 a a 2001:db8:0::1/64 dev veth0 ip netns exec B ip link set lo up ip netns exec B ip link set veth1 up ip netns exec B ip -6 a a 2001:db8:0::2/64 dev veth1 for i in {1..99}
do let A=$i-1 ip netns exec A ip link add ip6gre$i type ip6gre \ local 2001:db8:$A::1 remote 2001:db8:$A::2 encaplimit 100 ip netns exec A ip -6 a a 2001:db8:$i::1/64 dev ip6gre$i ip netns exec A ip link set ip6gre$i up
ip netns exec B ip link add ip6gre$i type ip6gre \ local 2001:db8:$A::2 remote 2001:db8:$A::1 encaplimit 100 ip netns exec B ip -6 a a 2001:db8:$i::2/64 dev ip6gre$i ip netns exec B ip link set ip6gre$i up done
Splat looks like: kernel BUG at net/core/skbuff.c:110! invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN PTI
CPU: 0 PID: 7 Comm: kworker/0:1 Not tainted 5.12.0+ #891 Workqueue: ipv6_addrconf addrconf_dad_work RIP: 0010:skb_panic+0x15d/0x15f Code: 92 fe 4c 8b 4c 24 10 53 8b 4d 70 45 89 e0 48 c7 c7 00 ae 79 83 41 57 41 56 41 55 48 8b 54 24 a6 26 f9 ff 0b 48 8b 6c 24 20 89 34 24 e8 4a 4e 92 fe 8b 34 24 48 c7 c1 20 RSP: 0018:ffff88810091f820 EFLAGS: 00010282 RAX: 0000000000000089 RBX: ffff8881086e9000 RCX: 0000000000000000 RDX: 0000000000000089 RSI: 0000000000000008 RDI: ffffed1020123efb RBP: ffff888005f6eac0 R08: ffffed1022fc0031 R09: ffffed1022fc0031 R10: ffff888117e00187 R11: ffffed1022fc0030 R12: 0000000000000028 R13: ffff888008284eb0 R14: 0000000000000ed8 R15: 0000000000000ec0 FS: 0000000000000000(0000) GS:ffff888117c00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f8b801c5640 CR3: 0000000033c2c006 CR4: 00000000003706f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: ? ip6_mc_hdr.isra.26.constprop.46+0x12a/0x600 ? ip6_mc_hdr.isra.26.constprop.46+0x12a/0x600 skb_put.cold.104+0x22/0x22 ip6_mc_hdr.isra.26.constprop.46+0x12a/0x600 ? rcu_read_lock_sched_held+0x91/0xc0 mld_newpack+0x398/0x8f0 ? ip6_mc_hdr.isra.26.constprop.46+0x600/0x600 ? lock_contended+0xc40/0xc40 add_grhead.isra.33+0x280/0x380 add_grec+0x5ca/0xff0 ? mld_sendpack+0xf40/0xf40 ? lock_downgrade+0x690/0x690 mld_send_initial_cr.part.34+0xb9/0x180 ipv6_mc_dad_complete+0x15d/0x1b0 addrconf_dad_completed+0x8d2/0xbb0 ? lock_downgrade+0x690/0x690 ? addrconf_rs_timer+0x660/0x660 ? addrconf_dad_work+0x73c/0x10e0 addrconf_dad_work+0x73c/0x10e0
Allowing high order page allocation could fix this problem.
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Analysis
by VulDB Data Team • 08/04/2025
The vulnerability described in CVE-2021-47146 resides within the Linux kernel's multicast listener discovery implementation, specifically within the mld_newpack() function. This flaw manifests as a kernel panic that occurs when attempting to allocate memory for network packets under certain conditions. The root cause lies in the function's strict limitation to order-0 memory page allocations, which are single page allocations of 4KB each. When the headroom size required for packet processing exceeds what can be accommodated within these constraints, the kernel's memory management subsystem triggers a panic during the skb_put() operation, which is responsible for adding data to socket buffers.
The technical execution of this vulnerability involves a specific sequence of operations that manipulate IPv6 multicast routing through virtual ethernet interfaces and GRE tunnels. The test commands demonstrate the creation of multiple network namespaces connected by virtual ethernet pairs, with each namespace hosting a series of GRE tunnel interfaces that establish complex routing paths. This configuration creates conditions where multicast packets must be processed through the mld_newpack() function, triggering the memory allocation failure. The kernel stack trace reveals the panic originates from net/core/skbuff.c at line 110, specifically in the skb_panic function, indicating a fundamental failure in socket buffer management when attempting to extend packet data beyond allocated boundaries.
The operational impact of this vulnerability is significant as it can lead to complete system crashes in kernel space, resulting in denial of service conditions that affect network functionality and potentially system availability. This type of vulnerability falls under the Common Weakness Enumeration category CWE-129, which deals with improper validation of array indices, and also relates to CWE-787, which involves out-of-bounds writes. The attack vector requires specific network configurations involving IPv6 multicast and GRE tunneling, making it less common but still potentially exploitable in environments with complex network topologies. From an ATT&CK framework perspective, this vulnerability maps to T1499.004, which involves network disruption through kernel-level attacks, and could potentially be leveraged for system compromise if combined with other primitives.
Mitigation strategies for CVE-2021-47146 primarily involve patching the kernel to allow high-order page allocations within the mld_newpack() function, which would provide more flexibility in memory allocation for packet processing. System administrators should prioritize applying the relevant kernel updates from their distribution vendors to address this issue. Additionally, network administrators can implement monitoring solutions to detect unusual multicast traffic patterns that might indicate exploitation attempts. The fix should be applied across all systems running affected kernel versions, particularly those handling complex IPv6 multicast configurations or environments with extensive GRE tunneling. Organizations should also consider implementing network segmentation and access controls to limit exposure to potentially malicious network configurations that could trigger this vulnerability.