CVE-2022-49658: Vulnerability in Linux Linux

Severity: highType: vulnerabilityCVE-2022-49658

In the Linux kernel, the following vulnerability has been resolved: bpf: Fix insufficient bounds propagation from adjust_scalar_min_max_vals Kuee reported a corner case where the tnum becomes constant after the call to __reg_bound_offset(), but the register's bounds are not, that is, its min bounds are still not equal to the register's max bounds. This in turn allows to leak pointers through turning a pointer register as is into an unknown scalar via adjust_ptr_min_max_vals(). Before: func#0 @0 0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 0: (b7) r0 = 1 ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) 1: (b7) r3 = 0 ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) 2: (87) r3 = -r3 ; R3_w=scalar() 3: (87) r3 = -r3 ; R3_w=scalar() 4: (47) r3 |= 32767 ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881) 5: (75) if r3 s>= 0x0 goto pc+1 ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 6: (95) exit from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 7: (d5) if r3 s<= 0x8000 goto pc+1 ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 8: (95) exit from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 9: (07) r3 += -32767 ; R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0)) <--- [*] 10: (95) exit What can be seen here is that R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) after the operation R3 += -32767 results in a 'malformed' constant, that is, R3_w=scalar(imm=0,umax=1,var_off=(0x0; 0x0)). Intersecting with var_off has not been done at that point via __update_reg_bounds(), which would have improved the umax to be equal to umin. Refactor the tnum <> min/max bounds information flow into a reg_bounds_sync() helper and use it consistently everywhere. After the fix, bounds have been corrected to R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) and thus the register is regarded as a 'proper' constant scalar of 0. After: func#0 @0 0: R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 0: (b7) r0 = 1 ; R0_w=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) 1: (b7) r3 = 0 ; R3_w=scalar(imm=0,umax=0,var_off=(0x0; 0x0)) 2: (87) r3 = -r3 ; R3_w=scalar() 3: (87) r3 = -r3 ; R3_w=scalar() 4: (47) r3 |= 32767 ; R3_w=scalar(smin=-9223372036854743041,umin=32767,var_off=(0x7fff; 0xffffffffffff8000),s32_min=-2147450881) 5: (75) if r3 s>= 0x0 goto pc+1 ; R3_w=scalar(umin=9223372036854808575,var_off=(0x8000000000007fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 6: (95) exit from 5 to 7: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881) R10=fp(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) 7: (d5) if r3 s<= 0x8000 goto pc+1 ; R3=scalar(umin=32769,umax=9223372036854775807,var_off=(0x7fff; 0x7fffffffffff8000),s32_min=-2147450881,u32_min=32767) 8: (95) exit from 7 to 9: R0=scalar(imm=1,umin=1,umax=1,var_off=(0x1; 0x0)) R1=ctx(off=0,imm=0,umax=0,var_off=(0x0; 0x0)) R3=scalar(umin=32767,umax=32768,var_off=(0x7fff; 0x8000)) R10=fp(off=0 ---truncated---

AI Analysis

Technical Summary

CVE-2022-49658 is a vulnerability in the Linux kernel's eBPF (extended Berkeley Packet Filter) subsystem, specifically related to insufficient bounds propagation in the function adjust_scalar_min_max_vals. The issue arises from a corner case where after the call to __reg_bound_offset(), the tnum (a representation of possible values a register can hold) becomes constant, but the register's bounds are not updated accordingly, leaving the minimum bounds unequal to the maximum bounds. This inconsistency allows an attacker to leak kernel pointers by converting a pointer register into an unknown scalar via adjust_ptr_min_max_vals(). The vulnerability is rooted in the improper synchronization between tnum and min/max bounds information flow, which was not consistently updated across the codebase. The fix involved refactoring this information flow into a reg_bounds_sync() helper function and applying it uniformly, ensuring that after the fix, registers are correctly recognized as proper constant scalars, preventing pointer leakage. The vulnerability affects specific Linux kernel versions identified by commit hashes, and no known exploits are reported in the wild as of the publication date. The vulnerability is technical and subtle, involving internal kernel register state tracking within eBPF verifier logic, which is critical for ensuring safe execution of eBPF programs. Exploiting this flaw could allow an attacker to bypass kernel memory protections by leaking kernel pointers, which can facilitate further attacks such as kernel address space layout randomization (KASLR) bypass and privilege escalation.

Potential Impact

For European organizations, the impact of CVE-2022-49658 can be significant, especially for those relying on Linux-based infrastructure, including servers, cloud environments, and embedded systems that utilize eBPF for networking, security monitoring, or performance tracing. Pointer leaks in the kernel can undermine the confidentiality and integrity of the system by enabling attackers to gather sensitive kernel memory layout information, which is a critical step in developing reliable kernel exploits. This can lead to privilege escalation and full system compromise. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure, which often deploy Linux extensively, could face increased risk if attackers leverage this vulnerability to gain unauthorized access or disrupt services. The absence of known exploits in the wild reduces immediate risk, but the technical nature of the vulnerability means that skilled attackers could develop exploits once the vulnerability details are public. The impact on availability is indirect but possible if attackers use the vulnerability as a stepping stone for further attacks that disrupt services.

Mitigation Recommendations

European organizations should apply the Linux kernel patches that address this vulnerability as soon as they become available from trusted sources or Linux distributions. Since this vulnerability involves the eBPF verifier, organizations should also consider restricting unprivileged eBPF usage where possible, as unprivileged userspace eBPF program loading can be a vector for exploitation. Specifically, administrators can disable unprivileged eBPF by setting /proc/sys/kernel/unprivileged_bpf_disabled to 1. Additionally, monitoring kernel logs for unusual eBPF activity and employing kernel integrity monitoring tools can help detect exploitation attempts. Organizations should ensure that their Linux kernel versions are up to date and track vendor advisories for backported fixes. For environments where immediate patching is not feasible, applying strict access controls and isolating critical systems can reduce exposure. Finally, security teams should educate developers and system administrators about the risks associated with eBPF and maintain a robust patch management process to quickly respond to such kernel vulnerabilities.