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Fri, 10 Apr 2026 14:10:41 +0800 (CST) From: Feng Yang To: ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, song@kernel.org, yonghong.song@linux.dev, jolsa@kernel.org, john.fastabend@gmail.com, kpsingh@kernel.org, mattbobrowski@google.com, jiayuan.chen@linux.dev Cc: bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org Subject: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc Date: Fri, 10 Apr 2026 14:10:36 +0800 Message-Id: <20260410061037.149532-2-yangfeng59949@163.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20260410061037.149532-1-yangfeng59949@163.com> References: <20260410061037.149532-1-yangfeng59949@163.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:PSgvCgDn739elNhpd0HuZg--.6807S3 X-Coremail-Antispam: 1Uf129KBjvAXoWfGFyDZFy7GF4xKF48Cr4rZrb_yoW8XrWUCo W3Gw4Yya18Gw1DJr9rCw1UXFW5ZF1rJa4xWa13XrZ8C3ZrZa4Dtr4DKr4rJ3yYqr4rGrZr C34fAr95uw1xJan3n29KB7ZKAUJUUUU8529EdanIXcx71UUUUU7v73VFW2AGmfu7bjvjm3 AaLaJ3UbIYCTnIWIevJa73UjIFyTuYvjxU79NVDUUUU X-CM-SenderInfo: p1dqww5hqjkmqzuzqiywtou0bp/xtbCzwHNRmnYlGELqwAA3h From: Feng Yang Using the following BPF program will cause a kernel panic: SEC("fmod_ret/security_task_alloc") int fmod_task_alloc(void *ctx) { return 1; } [ 383.899321] BUG: kernel NULL pointer dereference, address: 0000000000000b99 [ 383.899327] #PF: supervisor read access in kernel mode [ 383.899330] #PF: error_code(0x0000) - not-present page [ 383.899332] PGD 8000000108a60067 P4D 8000000108a60067 PUD 104550067 PMD 0 [ 383.899341] Oops: Oops: 0000 [#1] SMP PTI [ 383.899346] CPU: 1 UID: 0 PID: 12925 Comm: test Kdump: loaded Not tainted 7.0.0-rc6+ #1 PREEMPT(lazy) [ 383.899349] Hardware name: innotek GmbH VirtualBox/VirtualBox, BIOS VirtualBox 12/01/2006 [ 383.899351] RIP: 0010:get_task_pid+0x20/0x80 [ 383.899358] Code: 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 55 89 f5 53 48 89 fb e8 0b 98 0a 00 85 ed 75 32 48 81 c3 98 0b 00 00 <48> 8b 1b 48 85 db 74 14 b8 01 00 00 00 f0 0f c1 03 85 c0 74 27 8d [ 383.899362] RSP: 0018:ffffd3ca0ab13b38 EFLAGS: 00010206 [ 383.899367] RAX: 0000000000000001 RBX: 0000000000000b99 RCX: 0000000000000008 [ 383.899371] RDX: ffff8b2c85860000 RSI: 0000000000000000 RDI: 0000000000000001 [ 383.899374] RBP: 0000000000000000 R08: 0000010754cf50c8 R09: 0000010754cf50c8 [ 383.899377] R10: ffffffff95a6c000 R11: 0000000000000024 R12: 0000000000000000 [ 383.899380] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000001200000 [ 383.899384] FS: 00007f3eae907740(0000) GS:ffff8b2d05e5c000(0000) knlGS:0000000000000000 [ 383.899388] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 383.899390] CR2: 0000000000000b99 CR3: 0000000106a94003 CR4: 00000000000706f0 [ 383.899393] Call Trace: [ 383.899397] [ 383.899401] kernel_clone+0xe8/0x480 [ 383.899406] __do_sys_clone+0x65/0x90 [ 383.899410] do_syscall_64+0xca/0x860 [ 383.899421] ? next_uptodate_folio+0x85/0x2a0 [ 383.899427] ? percpu_counter_add_batch+0x4c/0x90 [ 383.899434] ? filemap_map_pages+0x3b7/0x4d0 [ 383.899437] ? do_read_fault+0x107/0x210 [ 383.899442] ? do_fault+0x1b2/0x330 [ 383.899445] ? __handle_mm_fault+0x49b/0x7a0 [ 383.899448] ? count_memcg_events+0xc4/0x160 [ 383.899453] ? handle_mm_fault+0xbb/0x370 [ 383.899456] ? do_user_addr_fault+0x209/0x680 [ 383.899459] ? irqentry_exit+0x7a/0x660 [ 383.899462] entry_SYSCALL_64_after_hwframe+0x76/0x7e [ 383.899466] RIP: 0033:0x7f3eaeb426e7 [ 383.899470] Code: 5d c3 90 f3 0f 1e fa 64 48 8b 04 25 10 00 00 00 45 31 c0 31 d2 31 f6 bf 11 00 20 01 4c 8d 90 d0 02 00 00 b8 38 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 39 89 c2 85 c0 75 2c 64 48 8b 04 25 10 00 00 [ 383.899472] RSP: 002b:00007fff23a2c838 EFLAGS: 00000246 ORIG_RAX: 0000000000000038 [ 383.899477] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007f3eaeb426e7 [ 383.899479] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000001200011 [ 383.899481] RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 [ 383.899483] R10: 00007f3eae907a10 R11: 0000000000000246 R12: 0000000000000001 [ 383.899485] R13: 00007fff23a2dbe8 R14: 0000000000403de0 R15: 00007f3eaecf5000 [ 383.899488] [ 383.899489] Modules linked in: nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 ip_set rfkill nf_tables sunrpc intel_rapl_msr intel_rapl_common intel_uncore_frequency_common intel_pmc_core pmt_telemetry snd_intel8x0 pmt_discovery pmt_class snd_ac97_codec intel_pmc_ssram_telemetry ac97_bus intel_vsec snd_pcm snd_timer snd rapl soundcore joydev sg i2c_piix4 pcspkr vboxguest i2c_smbus nfnetlink sr_mod cdrom sd_mod ata_generic vmwgfx ahci libahci ata_piix drm_ttm_helper ghash_clmulni_intel video ttm e1000 wmi libata serio_raw dm_mirror dm_region_hash dm_log dm_multipath dm_mod fuse i2c_dev autofs4 [ 383.899624] CR2: 0000000000000b99 This is because 1. The BPF program is designed to override the normal behavior of `security_task_alloc` and forcibly return a non-zero error value (e.g., `-ENOMEM` or `1`). 2. User space triggers a process creation syscall (like `fork` or `clone`). The kernel invokes `copy_process` to allocate and initialize a new `task_struct` for the child process. 3. `copy_process` invokes `security_task_alloc`. Due to the attached BPF program, it returns the positive value `1`. 4. `copy_process` treats any non-zero return from `security_task_alloc` as a failure. It aborts initialization, cleans up, and returns the error code cast to a pointer via `ERR_PTR(1)` (which evaluates to the memory address `0x1`). 5. In `kernel_clone()`, the kernel uses the `IS_ERR()` macro to check if the returned `task_struct *p` is an error pointer. However, `IS_ERR()` only checks for negative error codes in the range `[-MAX_ERRNO, -1]`. Since `0x1` is not in this range, the check `IS_ERR(p)` evaluates to `false`. 6. The kernel incorrectly assumes `p` is a valid `task_struct` pointer and proceeds to call `get_task_pid(p, PIDTYPE_PID)`. This dereferences the invalid address `0x1` (plus the offset of the `thread_pid` field), triggering a general protection fault or null-pointer dereference. Therefore, for security-related functions, similar to LSM, the validity of their return values is verified to fix the issue. Return value validation for fault injection is also added accordingly. Reported-by: Quan Sun <2022090917019@std.uestc.edu.cn> Reported-by: Yinhao Hu Reported-by: Kaiyan Mei Reviewed-by: Dongliang Mu Closes: https://lore.kernel.org/bpf/973a1b7b-8ee7-407a-890a-11455d9cc5bf@std.uestc.edu.cn/ Signed-off-by: Feng Yang --- kernel/bpf/verifier.c | 261 +++++++++++++++++++++++++++--------------- 1 file changed, 167 insertions(+), 94 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9c1135d373e2..37975e9a291c 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -18391,6 +18391,167 @@ static int check_ld_abs(struct bpf_verifier_env *env, struct bpf_insn *insn) return 0; } +#define SECURITY_PREFIX "security_" + +#ifdef CONFIG_FUNCTION_ERROR_INJECTION + +/* list of non-sleepable functions that are otherwise on + * ALLOW_ERROR_INJECTION list + */ +BTF_SET_START(btf_non_sleepable_error_inject) +/* Three functions below can be called from sleepable and non-sleepable context. + * Assume non-sleepable from bpf safety point of view. + */ +BTF_ID(func, __filemap_add_folio) +#ifdef CONFIG_FAIL_PAGE_ALLOC +BTF_ID(func, should_fail_alloc_page) +#endif +#ifdef CONFIG_FAILSLAB +BTF_ID(func, should_failslab) +#endif +BTF_SET_END(btf_non_sleepable_error_inject) + +static int check_non_sleepable_error_inject(u32 btf_id) +{ + return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id); +} + +static int check_attach_sleepable(u32 btf_id, unsigned long addr, const char *func_name) +{ + /* fentry/fexit/fmod_ret progs can be sleepable if they are + * attached to ALLOW_ERROR_INJECTION and are not in denylist. + */ + if (!check_non_sleepable_error_inject(btf_id) && + within_error_injection_list(addr)) + return 0; + + return -EINVAL; +} + +static int check_attach_modify_return(unsigned long addr, const char *func_name) +{ + if (within_error_injection_list(addr) || + !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1)) + return 0; + + return -EINVAL; +} + +static int modify_return_get_retval_range(const struct bpf_prog *prog, + struct bpf_retval_range *retval_range) +{ + unsigned long addr = (unsigned long)prog->aux->dst_trampoline->func.addr; + + if (within_error_injection_list(addr)) { + switch (get_injectable_error_type(addr)) { + case EI_ETYPE_NULL: + retval_range->minval = 0; + retval_range->maxval = 0; + break; + case EI_ETYPE_ERRNO: + retval_range->minval = -MAX_ERRNO; + retval_range->maxval = -1; + break; + case EI_ETYPE_ERRNO_NULL: + retval_range->minval = -MAX_ERRNO; + retval_range->maxval = 0; + break; + case EI_ETYPE_TRUE: + retval_range->minval = 1; + retval_range->maxval = 1; + break; + } + retval_range->return_32bit = true; + + return 0; + } + + return -EINVAL; +} + +#else + +/* Unfortunately, the arch-specific prefixes are hard-coded in arch syscall code + * so we need to hard-code them, too. Ftrace has arch_syscall_match_sym_name() + * but that just compares two concrete function names. + */ +static bool has_arch_syscall_prefix(const char *func_name) +{ +#if defined(__x86_64__) + return !strncmp(func_name, "__x64_", 6); +#elif defined(__i386__) + return !strncmp(func_name, "__ia32_", 7); +#elif defined(__s390x__) + return !strncmp(func_name, "__s390x_", 8); +#elif defined(__aarch64__) + return !strncmp(func_name, "__arm64_", 8); +#elif defined(__riscv) + return !strncmp(func_name, "__riscv_", 8); +#elif defined(__powerpc__) || defined(__powerpc64__) + return !strncmp(func_name, "sys_", 4); +#elif defined(__loongarch__) + return !strncmp(func_name, "sys_", 4); +#else + return false; +#endif +} + +/* Without error injection, allow sleepable and fmod_ret progs on syscalls. */ + +static int check_attach_sleepable(u32 btf_id, unsigned long addr, const char *func_name) +{ + if (has_arch_syscall_prefix(func_name)) + return 0; + + return -EINVAL; +} + +static int check_attach_modify_return(unsigned long addr, const char *func_name) +{ + if (has_arch_syscall_prefix(func_name) || + !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1)) + return 0; + + return -EINVAL; +} + +/* The system call return value is allowed to be an arbitrary value. */ +static int modify_return_get_retval_range(const struct bpf_prog *prog, + struct bpf_retval_range *retval_range) +{ + return -EINVAL; +} + +#endif /* CONFIG_FUNCTION_ERROR_INJECTION */ + +/* hooks return 0 or 1 */ +BTF_SET_START(bool_security_hooks) +BTF_ID(func, security_xfrm_state_pol_flow_match) +BTF_ID(func, security_audit_rule_known) +BTF_ID(func, security_inode_xattr_skipcap) +BTF_SET_END(bool_security_hooks) + +/* Similar to bpf_lsm_get_retval_range, + * ensure that the return values of fmod_ret are valid. + */ +static int bpf_security_get_retval_range(const struct bpf_prog *prog, + struct bpf_retval_range *retval_range) +{ + if (strncmp(SECURITY_PREFIX, prog->aux->attach_func_name, + sizeof(SECURITY_PREFIX) - 1)) + return -EINVAL; + + if (btf_id_set_contains(&bool_security_hooks, prog->aux->attach_btf_id)) { + retval_range->minval = 0; + retval_range->maxval = 1; + } else { + retval_range->minval = -MAX_ERRNO; + retval_range->maxval = 0; + } + retval_range->return_32bit = true; + + return 0; +} static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_range *range) { @@ -18444,8 +18605,13 @@ static bool return_retval_range(struct bpf_verifier_env *env, struct bpf_retval_ *range = retval_range(0, 0); break; case BPF_TRACE_RAW_TP: - case BPF_MODIFY_RETURN: return false; + case BPF_MODIFY_RETURN: + if (!bpf_security_get_retval_range(env->prog, range)) + break; + if (modify_return_get_retval_range(env->prog, range)) + return false; + break; case BPF_TRACE_ITER: default: break; @@ -25487,99 +25653,6 @@ static int check_struct_ops_btf_id(struct bpf_verifier_env *env) return bpf_prog_ctx_arg_info_init(prog, st_ops_desc->arg_info[member_idx].info, st_ops_desc->arg_info[member_idx].cnt); } -#define SECURITY_PREFIX "security_" - -#ifdef CONFIG_FUNCTION_ERROR_INJECTION - -/* list of non-sleepable functions that are otherwise on - * ALLOW_ERROR_INJECTION list - */ -BTF_SET_START(btf_non_sleepable_error_inject) -/* Three functions below can be called from sleepable and non-sleepable context. - * Assume non-sleepable from bpf safety point of view. - */ -BTF_ID(func, __filemap_add_folio) -#ifdef CONFIG_FAIL_PAGE_ALLOC -BTF_ID(func, should_fail_alloc_page) -#endif -#ifdef CONFIG_FAILSLAB -BTF_ID(func, should_failslab) -#endif -BTF_SET_END(btf_non_sleepable_error_inject) - -static int check_non_sleepable_error_inject(u32 btf_id) -{ - return btf_id_set_contains(&btf_non_sleepable_error_inject, btf_id); -} - -static int check_attach_sleepable(u32 btf_id, unsigned long addr, const char *func_name) -{ - /* fentry/fexit/fmod_ret progs can be sleepable if they are - * attached to ALLOW_ERROR_INJECTION and are not in denylist. - */ - if (!check_non_sleepable_error_inject(btf_id) && - within_error_injection_list(addr)) - return 0; - - return -EINVAL; -} - -static int check_attach_modify_return(unsigned long addr, const char *func_name) -{ - if (within_error_injection_list(addr) || - !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1)) - return 0; - - return -EINVAL; -} - -#else - -/* Unfortunately, the arch-specific prefixes are hard-coded in arch syscall code - * so we need to hard-code them, too. Ftrace has arch_syscall_match_sym_name() - * but that just compares two concrete function names. - */ -static bool has_arch_syscall_prefix(const char *func_name) -{ -#if defined(__x86_64__) - return !strncmp(func_name, "__x64_", 6); -#elif defined(__i386__) - return !strncmp(func_name, "__ia32_", 7); -#elif defined(__s390x__) - return !strncmp(func_name, "__s390x_", 8); -#elif defined(__aarch64__) - return !strncmp(func_name, "__arm64_", 8); -#elif defined(__riscv) - return !strncmp(func_name, "__riscv_", 8); -#elif defined(__powerpc__) || defined(__powerpc64__) - return !strncmp(func_name, "sys_", 4); -#elif defined(__loongarch__) - return !strncmp(func_name, "sys_", 4); -#else - return false; -#endif -} - -/* Without error injection, allow sleepable and fmod_ret progs on syscalls. */ - -static int check_attach_sleepable(u32 btf_id, unsigned long addr, const char *func_name) -{ - if (has_arch_syscall_prefix(func_name)) - return 0; - - return -EINVAL; -} - -static int check_attach_modify_return(unsigned long addr, const char *func_name) -{ - if (has_arch_syscall_prefix(func_name) || - !strncmp(SECURITY_PREFIX, func_name, sizeof(SECURITY_PREFIX) - 1)) - return 0; - - return -EINVAL; -} - -#endif /* CONFIG_FUNCTION_ERROR_INJECTION */ int bpf_check_attach_target(struct bpf_verifier_log *log, const struct bpf_prog *prog, -- 2.43.0