Executive Summary

This vulnerability exists in the Linux kernel's BPF (Berkeley Packet Filter) verifier related to the BPF_END operation, which performs a byte swap on a register's scalar value.

When a register undergoes a BPF_END operation, its scalar value is changed in place. If this register previously shared a scalar ID with another register (for example, after an assignment like r1 = r0), this connection should be broken.

However, the verifier fails to reset the register's ID to zero after the BPF_END operation. As a result, if a conditional jump checks the swapped register, the verifier incorrectly propagates the bounds it learned to the linked register, causing false confidence in the linked register's value.

This can potentially allow out-of-bounds memory accesses, which is a security risk.

The fix involves explicitly resetting the register's ID to zero during the BPF_END case to break the scalar tie, similar to how the BPF_NEG operation handles it.

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Impact Analysis

This vulnerability can lead to out-of-bounds memory accesses in the Linux kernel's BPF subsystem.

Such out-of-bounds accesses may allow attackers to read or write memory locations they should not have access to, potentially leading to system crashes, data corruption, or privilege escalation.

Therefore, systems running vulnerable versions of the Linux kernel could be at risk of exploitation through crafted BPF programs.

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Mitigation Strategies

The vulnerability has been resolved in the Linux kernel by resetting the register ID for BPF_END value tracking to prevent incorrect propagation of bounds and potential out-of-bounds memory accesses.

To mitigate this vulnerability, you should update your Linux kernel to a version that includes this fix.

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