CVE-2022-49197

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

af_netlink: Fix shift out of bounds in group mask calculation

When a netlink message is received, netlink_recvmsg() fills in the address of the sender. One of the fields is the 32-bit bitfield nl_groups, which carries the multicast group on which the message was received. The least significant bit corresponds to group 1, and therefore the highest group that the field can represent is 32. Above that, the UB sanitizer flags the out-of-bounds shift attempts.

Which bits end up being set in such case is implementation defined, but its either going to be a wrong non-zero value, or zero, which is at least not misleading. Make the latter choice deterministic by always setting to 0 for higher-numbered multicast groups.

To get information about membership in groups >= 32, userspace is expected to use nl_pktinfo control messages[0], which are enabled by NETLINK_PKTINFO socket option. [0] https://lwn.net/Articles/147608/

The way to trigger this issue is e.g. through monitoring the BRVLAN group:

# bridge monitor vlan &
# ip link add name br type bridge

Which produces the following citation:

UBSAN: shift-out-of-bounds in net/netlink/af_netlink.c:162:19
shift exponent 32 is too large for 32-bit type int

Weakness

The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.

Affected Software

Potential Mitigations

• Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
• If possible, choose a language or compiler that performs automatic bounds checking.
• Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
• Use libraries or frameworks that make it easier to handle numbers without unexpected consequences.
• Examples include safe integer handling packages such as SafeInt (C++) or IntegerLib (C or C++). [REF-106]
• Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
• Use unsigned integers where possible. This makes it easier to perform validation for integer overflows. When signed integers are required, ensure that the range check includes minimum values as well as maximum values.
• Understand the programming language’s underlying representation and how it interacts with numeric calculation (CWE-681). Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, “not-a-number” calculations, and how the language handles numbers that are too large or too small for its underlying representation. [REF-7]
• Also be careful to account for 32-bit, 64-bit, and other potential differences that may affect the numeric representation.

Related Attack Patterns

• https://cwe.mitre.org/data/definitions/92.html

References

• https://git.kernel.org/stable/c/0caf6d9922192dd1afa8dc2131abfb4df1443b9f
• https://git.kernel.org/stable/c/41249fff507387c3323b198d0052faed08b14de4
• https://git.kernel.org/stable/c/7409ff6393a67ff9838d0ae1bd102fb5f020d07a
• https://git.kernel.org/stable/c/ac5883a8890a11c00b32a19949a25d4afeaa2f5a
• https://git.kernel.org/stable/c/b0898362188e05b2202656058cc32d98fabf3bac
• https://git.kernel.org/stable/c/e1c5d46f05aa23d740daae5cd3a6472145afac42
• https://git.kernel.org/stable/c/e23e1e981247feb3c7d0236fe58aceb685f234ae
• https://git.kernel.org/stable/c/e8aaf3134bc5e943048eefe9f2ddaabf41d92b1a
• https://git.kernel.org/stable/c/f75f4abeec4c04b600a15b50c89a481f1e7435ee