CVE-2021-46992

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nftables: avoid overflows in nft_hash_buckets()

Number of buckets being stored in 32bit variables, we have to ensure that no overflows occur in nft_hash_buckets()

syzbot injected a size == 0x40000000 and reported:

UBSAN: shift-out-of-bounds in ./include/linux/log2.h:57:13 shift exponent 64 is too large for 64-bit type long unsigned int CPU: 1 PID: 29539 Comm: syz-executor.4 Not tainted 5.12.0-rc7-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:79 [inline] dump_stack+0x141/0x1d7 lib/dump_stack.c:120 ubsan_epilogue+0xb/0x5a lib/ubsan.c:148 __ubsan_handle_shift_out_of_bounds.cold+0xb1/0x181 lib/ubsan.c:327 __roundup_pow_of_two include/linux/log2.h:57 [inline] nft_hash_buckets net/netfilter/nft_set_hash.c:411 [inline] nft_hash_estimate.cold+0x19/0x1e net/netfilter/nft_set_hash.c:652 nft_select_set_ops net/netfilter/nf_tables_api.c:3586 [inline] nf_tables_newset+0xe62/0x3110 net/netfilter/nf_tables_api.c:4322 nfnetlink_rcv_batch+0xa09/0x24b0 net/netfilter/nfnetlink.c:488 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:612 [inline] nfnetlink_rcv+0x3af/0x420 net/netfilter/nfnetlink.c:630 netlink_unicast_kernel net/netlink/af_netlink.c:1312 [inline] netlink_unicast+0x533/0x7d0 net/netlink/af_netlink.c:1338 netlink_sendmsg+0x856/0xd90 net/netlink/af_netlink.c:1927 sock_sendmsg_nosec net/socket.c:654 [inline] sock_sendmsg+0xcf/0x120 net/socket.c:674 ____sys_sendmsg+0x6e8/0x810 net/socket.c:2350 ___sys_sendmsg+0xf3/0x170 net/socket.c:2404 __sys_sendmsg+0xe5/0x1b0 net/socket.c:2433 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46

Weakness

The product reads data past the end, or before the beginning, of the intended buffer.

Affected Software

Potential Mitigations

• Assume all input is malicious. Use an “accept known good” input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
• When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, “boat” may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as “red” or “blue.”
• Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code’s environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
• To reduce the likelihood of introducing an out-of-bounds read, ensure that you validate and ensure correct calculations for any length argument, buffer size calculation, or offset. Be especially careful of relying on a sentinel (i.e. special character such as NUL) in untrusted inputs.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/540.html

References

• https://git.kernel.org/stable/c/1e8ab479cfbe5751efccedb95afb9b112a5ba475
• https://git.kernel.org/stable/c/2824cafc6a93792d9ad85939c499161214d84c4b
• https://git.kernel.org/stable/c/72b49dd116ca00a46a11d5a4d8d7987f05ed9cd7
• https://git.kernel.org/stable/c/a388d10961ff8578b1a6691945d406c0f33aa71b
• https://git.kernel.org/stable/c/a54754ec9891830ba548e2010c889e3c8146e449
• https://git.kernel.org/stable/c/c77e2ef18167ad334e27610ced9a7f6af5ec1787
• https://git.kernel.org/stable/c/efcd730ddd6f25578bd31bfe703e593e2421d708
• https://git.kernel.org/stable/c/1e8ab479cfbe5751efccedb95afb9b112a5ba475
• https://git.kernel.org/stable/c/2824cafc6a93792d9ad85939c499161214d84c4b
• https://git.kernel.org/stable/c/72b49dd116ca00a46a11d5a4d8d7987f05ed9cd7
• https://git.kernel.org/stable/c/a388d10961ff8578b1a6691945d406c0f33aa71b
• https://git.kernel.org/stable/c/a54754ec9891830ba548e2010c889e3c8146e449
• https://git.kernel.org/stable/c/c77e2ef18167ad334e27610ced9a7f6af5ec1787
• https://git.kernel.org/stable/c/efcd730ddd6f25578bd31bfe703e593e2421d708