CVE-2022-49985 in Linux
Summary
by MITRE • 06/18/2025
In the Linux kernel, the following vulnerability has been resolved:
bpf: Don't use tnum_range on array range checking for poke descriptors
Hsin-Wei reported a KASAN splat triggered by their BPF runtime fuzzer which is based on a customized syzkaller:
BUG: KASAN: slab-out-of-bounds in bpf_int_jit_compile+0x1257/0x13f0 Read of size 8 at addr ffff888004e90b58 by task syz-executor.0/1489 CPU: 1 PID: 1489 Comm: syz-executor.0 Not tainted 5.19.0 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x9c/0xc9 print_address_description.constprop.0+0x1f/0x1f0 ? bpf_int_jit_compile+0x1257/0x13f0 kasan_report.cold+0xeb/0x197 ? kvmalloc_node+0x170/0x200 ? bpf_int_jit_compile+0x1257/0x13f0 bpf_int_jit_compile+0x1257/0x13f0 ? arch_prepare_bpf_dispatcher+0xd0/0xd0 ? rcu_read_lock_sched_held+0x43/0x70 bpf_prog_select_runtime+0x3e8/0x640 ? bpf_obj_name_cpy+0x149/0x1b0 bpf_prog_load+0x102f/0x2220 ? __bpf_prog_put.constprop.0+0x220/0x220 ? find_held_lock+0x2c/0x110 ? __might_fault+0xd6/0x180 ? lock_downgrade+0x6e0/0x6e0 ? lock_is_held_type+0xa6/0x120 ? __might_fault+0x147/0x180 __sys_bpf+0x137b/0x6070 ? bpf_perf_link_attach+0x530/0x530 ? new_sync_read+0x600/0x600 ? __fget_files+0x255/0x450 ? lock_downgrade+0x6e0/0x6e0 ? fput+0x30/0x1a0 ? ksys_write+0x1a8/0x260 __x64_sys_bpf+0x7a/0xc0 ? syscall_enter_from_user_mode+0x21/0x70 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd RIP: 0033:0x7f917c4e2c2d
The problem here is that a range of tnum_range(0, map->max_entries - 1) has limited ability to represent the concrete tight range with the tnum as the set of resulting states from value + mask can result in a superset of the actual intended range, and as such a tnum_in(range, reg->var_off) check may yield true when it shouldn't, for example tnum_range(0, 2) would result in 00XX -> v = 0000, m = 0011 such that the intended set of {0, 1, 2} is here
represented by a less precise superset of {0, 1, 2, 3}. As the register is
known const scalar, really just use the concrete reg->var_off.value for the upper index check.
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Analysis
by VulDB Data Team • 11/30/2025
The vulnerability CVE-2022-49985 affects the Linux kernel's BPF (Berkeley Packet Filter) subsystem and specifically targets the handling of array range checking during poke descriptor operations. This issue manifests as a slab-out-of-bounds memory access error that triggers a KASAN (Kernel Address Sanitizer) warning, indicating a potential security risk that could lead to memory corruption or privilege escalation. The vulnerability was discovered through fuzzing using a customized syzkaller runtime environment, highlighting the importance of comprehensive testing in kernel security. The problem originates from the bpf_int_jit_compile function where improper range checking logic leads to incorrect memory access patterns. The root cause lies in how the kernel represents value ranges using tnum_range structures, which can produce imprecise superset representations that fail to accurately reflect the intended concrete ranges.
The technical flaw stems from the use of tnum_range for array bounds checking when processing BPF poke descriptors, where the range representation fails to maintain precision during arithmetic operations. Specifically, when dealing with a range such as tnum_range(0, map->max_entries - 1), the system employs a technique that uses value plus mask representation to model ranges. This approach can result in situations where the actual intended range {0, 1, 2} gets represented as a less precise superset {0, 1, 2, 3} due to how the mask operations work. The issue occurs because tnum_range operations can generate sets of resulting states that encompass more values than the actual intended range, causing false positives in range validation checks. When the code performs a tnum_in(range, reg->var_off) check, it incorrectly validates against the imprecise superset rather than the concrete intended range, leading to out-of-bounds memory access. This represents a classic case of over-approximation in static analysis where the abstraction used for range checking introduces false positives that can be exploited.
The operational impact of this vulnerability extends beyond simple memory corruption, potentially enabling attackers to exploit the kernel's BPF JIT compiler to perform unauthorized memory operations or escalate privileges. Since BPF programs can be loaded by unprivileged users and executed with kernel-level privileges, this vulnerability could be leveraged in privilege escalation attacks. The vulnerability affects systems running Linux kernel versions where the BPF subsystem is enabled and used, particularly those with JIT compilation capabilities. The memory access violation occurs during program compilation when the kernel attempts to validate array bounds, making it a critical issue that could be triggered by malicious BPF program loading. The nature of the vulnerability makes it particularly dangerous in containerized environments or systems where untrusted code execution is possible, as it could be exploited to bypass security boundaries. This vulnerability also highlights the complexity of kernel-level static analysis and the challenges of maintaining precise range representations in just-in-time compilation environments.
The recommended mitigation strategy involves modifying the BPF JIT compiler to use concrete value representations instead of imprecise range approximations when performing array bounds checking for poke descriptors. The fix specifically addresses the issue by replacing tnum_range operations with direct concrete value comparisons when dealing with known constant scalar registers. This approach ensures that the upper index check uses the actual concrete value from reg->var_off.value rather than relying on potentially imprecise range representations. The solution aligns with security best practices for kernel development, emphasizing the importance of precise range checking in memory safety-critical code paths. System administrators should apply the relevant kernel patches as soon as possible, particularly on systems running BPF-enabled kernels where the vulnerability could be exploited. Organizations should also consider implementing additional monitoring for BPF program loading activities and ensuring that only trusted code is allowed to load BPF programs. This vulnerability demonstrates the importance of continuous security auditing of kernel subsystems and the need for robust testing methodologies that can uncover subtle issues in complex systems like the Linux kernel's JIT compiler infrastructure. The fix essentially implements a more conservative approach to range checking that prioritizes correctness over potential performance optimizations that could introduce security flaws.