[PATCH v2 bpf-next 0/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[PATCH v2 bpf-next 0/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

From: Feng Yang <yangfeng@kylinos.cn>

This patch set adds return value validation for fmod_ret
to prevent system crashes caused by incorrect return values.

Changes in v2:
- Add validation for fault injection and include selftests. Thanks, Jiri
  Olsa, Jiayuan Chen.
- Link to v1: https://lore.kernel.org/all/20260408094816.228322-1-yangfeng59949@163.com/


Feng Yang (2):
  bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret
    on security_task_alloc
  selftests/bpf: Add selftests for verifying return values of fmod_ret.

 kernel/bpf/verifier.c                         | 261 +++++++++++-------
 .../selftests/bpf/prog_tests/verifier.c       |   2 +
 .../bpf/progs/verifier_fmod_ret_return.c      |  60 ++++
 3 files changed, 229 insertions(+), 94 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_fmod_ret_return.c

-- 
2.43.0

[PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

From: Feng Yang <yangfeng@kylinos.cn>

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]  <TASK>
[  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]  </TASK>
[  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 <dddddd@hust.edu.cn>
Reported-by: Kaiyan Mei <M202472210@hust.edu.cn>
Reviewed-by: Dongliang Mu <dzm91@hust.edu.cn>
Closes: https://lore.kernel.org/bpf/973a1b7b-8ee7-407a-890a-11455d9cc5bf@std.uestc.edu.cn/
Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
---
 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

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[bot+bpf-ci]

[-- Attachment #1: Type: text/plain, Size: 2318 bytes --]

> 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

[ ... ]

> +/* 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)

There are two issues with this BTF set.

First, security_inode_xattr_skipcap does not exist as a kernel function.
The LSM hook inode_xattr_skipcap is only invoked via call_int_hook()
inside security_inode_setxattr() and security_inode_removexattr().
There is no standalone security_inode_xattr_skipcap() wrapper. The
equivalent entry in bool_lsm_hooks in kernel/bpf/bpf_lsm.c correctly
references bpf_lsm_inode_xattr_skipcap instead.

Second, the v1 of this patch had #ifdef guards matching those in
bool_lsm_hooks:

    #ifdef CONFIG_SECURITY_NETWORK_XFRM
    BTF_ID(func, security_xfrm_state_pol_flow_match)
    #endif
    #ifdef CONFIG_AUDIT
    BTF_ID(func, security_audit_rule_known)
    #endif

These guards were dropped in v2. security_xfrm_state_pol_flow_match
is defined under CONFIG_SECURITY_NETWORK_XFRM in security/security.c,
and security_audit_rule_known is defined under CONFIG_AUDIT. Without
the guards, BTF_IDs will be unresolvable when those configs are
disabled.

> +
> +/* Similar to bpf_lsm_get_retval_range,
> + * ensure that the return values of fmod_ret are valid.
> + */

This isn't a bug, but the BPF subsystem uses the kernel multi-line
comment style where the opening /* goes on its own line:

    /*
     * Similar to bpf_lsm_get_retval_range,
     * ensure that the return values of fmod_ret are valid.
     */

[ ... ]

This commit appears to be a major bug fix addressing a kernel NULL
pointer dereference but is missing a Fixes: tag. The bug was
introduced when fmod_ret was first allowed on security_* functions
without return value validation:

    Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/24229694699

[PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

On Fri, 10 Apr 2026 07:00:25, bot+bpf-ci@kernel.org wrote:

> > 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
> 
> [ ... ]
> 
> > +/* 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)
> 
> There are two issues with this BTF set.
> 
> First, security_inode_xattr_skipcap does not exist as a kernel function.
> The LSM hook inode_xattr_skipcap is only invoked via call_int_hook()
> inside security_inode_setxattr() and security_inode_removexattr().
> There is no standalone security_inode_xattr_skipcap() wrapper. The
> equivalent entry in bool_lsm_hooks in kernel/bpf/bpf_lsm.c correctly
> references bpf_lsm_inode_xattr_skipcap instead.
> 

Yes, and in fact, the return values of `security_inode_removexattr` and `security_inode_setxattr` 
can be those of `inode_removexattr` and `inode_setxattr` respectively, so the 0-1 restriction is not necessary here.

> Second, the v1 of this patch had #ifdef guards matching those in
> bool_lsm_hooks:
> 
>     #ifdef CONFIG_SECURITY_NETWORK_XFRM
>     BTF_ID(func, security_xfrm_state_pol_flow_match)
>     #endif
>     #ifdef CONFIG_AUDIT
>     BTF_ID(func, security_audit_rule_known)
>     #endif
> 
> These guards were dropped in v2. security_xfrm_state_pol_flow_match
> is defined under CONFIG_SECURITY_NETWORK_XFRM in security/security.c,
> and security_audit_rule_known is defined under CONFIG_AUDIT. Without
> the guards, BTF_IDs will be unresolvable when those configs are
> disabled.

I saw there was a default return prototype even without the corresponding config,
and assumed that hooking would still work without it, so I removed the config guards.
However, I didn't notice that these are inline functions and cannot be hooked.
I will revert this change in the next version.

> > +
> > +/* Similar to bpf_lsm_get_retval_range,
> > + * ensure that the return values of fmod_ret are valid.
> > + */
> 
> This isn't a bug, but the BPF subsystem uses the kernel multi-line
> comment style where the opening /* goes on its own line:
> 
>     /*
>      * Similar to bpf_lsm_get_retval_range,
>      * ensure that the return values of fmod_ret are valid.
>      */
> 
> [ ... ]
> 
> This commit appears to be a major bug fix addressing a kernel NULL
> pointer dereference but is missing a Fixes: tag. The bug was
> introduced when fmod_ret was first allowed on security_* functions
> without return value validation:
> 
>     Fixes: 6ba43b761c41 ("bpf: Attachment verification for BPF_MODIFY_RETURN")
> 
Thanks.

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Leon Hwang]

On 10/4/26 14:10, Feng Yang wrote:
> From: Feng Yang <yangfeng@kylinos.cn>
> 

[...]

> +
> +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;
> +}

Why did you move them here? Seems that you didn't use them.

> +
> +static int modify_return_get_retval_range(const struct bpf_prog *prog,
> +					  struct bpf_retval_range *retval_range)

NIT: code format issue here.

Thanks,
Leon

> +{
[...]

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Leon Hwang]

On 10/4/26 15:21, Leon Hwang wrote:
> On 10/4/26 14:10, Feng Yang wrote:
>> From: Feng Yang <yangfeng@kylinos.cn>
>>
> 
> [...]
> 
>> +
>> +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;
>> +}
> 
> Why did you move them here? Seems that you didn't use them.
> 
>> +
>> +static int modify_return_get_retval_range(const struct bpf_prog *prog,
>> +					  struct bpf_retval_range *retval_range)
> 
> NIT: code format issue here.
> 

Sorry about this. It is false. I was misled by thunderbird.

> Thanks,
> Leon
> 
>> +{
> [...]
> 

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

On Fri, 10 Apr 2026 15:21:26 +0800 Leon Hwang wrote:
> On 10/4/26 14:10, Feng Yang wrote:
> > From: Feng Yang <yangfeng@kylinos.cn>
> > 
> 
> [...]
> 
> > +
> > +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;
> > +}
> 
> Why did you move them here? Seems that you didn't use them.

Because CONFIG_FUNCTION_ERROR_INJECTION is directly reused here,
and the function has_arch_syscall_prefix is intended to be used.

> > +
> > +static int modify_return_get_retval_range(const struct bpf_prog *prog,
> > +					  struct bpf_retval_range *retval_range)
> 
> NIT: code format issue here.

Thanks.

> Thanks,
> Leon
> 
> > +{
> [...]

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Leon Hwang]

On 10/4/26 15:40, Feng Yang wrote:
> On Fri, 10 Apr 2026 15:21:26 +0800 Leon Hwang wrote:
>> On 10/4/26 14:10, Feng Yang wrote:
>>> From: Feng Yang <yangfeng@kylinos.cn>
>>>
>>
>> [...]
>>
>>> +
>>> +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;
>>> +}
>>
>> Why did you move them here? Seems that you didn't use them.
> 
> Because CONFIG_FUNCTION_ERROR_INJECTION is directly reused here,
> and the function has_arch_syscall_prefix is intended to be used.
> 

You can declare the function instead. No?

But, the function has_arch_syscall_prefix was not used in your new code?

Thanks,
Leon

[PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

On Fri, 10 Apr 2026 15:49:15 +0800, Leon Hwang wrote:
> On 10/4/26 15:40, Feng Yang wrote:
> > On Fri, 10 Apr 2026 15:21:26 +0800 Leon Hwang wrote:
> >> On 10/4/26 14:10, Feng Yang wrote:
> >>> From: Feng Yang <yangfeng@kylinos.cn>
> >>>
> >>
> >> [...]
> >>
> >>> +
> >>> +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;
> >>> +}
> >>
> >> Why did you move them here? Seems that you didn't use them.
> > 
> > Because CONFIG_FUNCTION_ERROR_INJECTION is directly reused here,
> > and the function has_arch_syscall_prefix is intended to be used.
> > 
> 
> You can declare the function instead. No?
> 
> But, the function has_arch_syscall_prefix was not used in your new code?

Indeed, I will fix it in the next version. Thank you.

> Thanks,
> Leon

[PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Feng Yang]

[...]
> +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;

This refers to the documentation in fault-injection.rst:

Each error injectable functions will have the error type specified by the
ALLOW_ERROR_INJECTION() macro. You have to choose it carefully if you add
a new error injectable function. If the wrong error type is chosen, the
kernel may crash because it may not be able to handle the error.
There are 4 types of errors defined in include/asm-generic/error-injection.h

EI_ETYPE_NULL
  This function will return `NULL` if it fails. e.g. return an allocated
  object address.

EI_ETYPE_ERRNO
  This function will return an `-errno` error code if it fails. e.g. return
  -EINVAL if the input is wrong. This will include the functions which will
  return an address which encodes `-errno` by ERR_PTR() macro.

EI_ETYPE_ERRNO_NULL
  This function will return an `-errno` or `NULL` if it fails. If the caller
  of this function checks the return value with IS_ERR_OR_NULL() macro, this
  type will be appropriate.

EI_ETYPE_TRUE
  This function will return `true` (non-zero positive value) if it fails.

Restrict EI_ETYPE_ERRNO to only return error codes.
However, it was noticed that the self-test bpf_testmod_test_read uses 
ALLOW_ERROR_INJECTION(bpf_testmod_test_read, ERRNO); and returns 0, which causes a failure.
So should returning 0 be considered valid for the EI_ETYPE_ERRNO type, or should the self-test be modified instead?

Thanks.

> +		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;
> +}

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Leon Hwang]

On 10/4/26 16:03, Feng Yang wrote:
> [...]
>> +static int modify_return_get_retval_range(const struct bpf_prog *prog,
>> +					  struct bpf_retval_range *retval_range)

How about 'range' instead of 'retval_range' like its caller?

>> +{
>> +	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;
> 
> This refers to the documentation in fault-injection.rst:
> 
> Each error injectable functions will have the error type specified by the
> ALLOW_ERROR_INJECTION() macro. You have to choose it carefully if you add
> a new error injectable function. If the wrong error type is chosen, the
> kernel may crash because it may not be able to handle the error.
> There are 4 types of errors defined in include/asm-generic/error-injection.h
> 
> EI_ETYPE_NULL
>   This function will return `NULL` if it fails. e.g. return an allocated
>   object address.
> 
> EI_ETYPE_ERRNO
>   This function will return an `-errno` error code if it fails. e.g. return
>   -EINVAL if the input is wrong. This will include the functions which will
>   return an address which encodes `-errno` by ERR_PTR() macro.
> 
> EI_ETYPE_ERRNO_NULL
>   This function will return an `-errno` or `NULL` if it fails. If the caller
>   of this function checks the return value with IS_ERR_OR_NULL() macro, this
>   type will be appropriate.
> 
> EI_ETYPE_TRUE
>   This function will return `true` (non-zero positive value) if it fails.
> 
> Restrict EI_ETYPE_ERRNO to only return error codes.
> However, it was noticed that the self-test bpf_testmod_test_read uses 
> ALLOW_ERROR_INJECTION(bpf_testmod_test_read, ERRNO); and returns 0, which causes a failure.
> So should returning 0 be considered valid for the EI_ETYPE_ERRNO type, or should the self-test be modified instead?
> 
I think it would be better to add such explanation in code comment.

Thanks,
Leon

Re: [PATCH v2 bpf-next 1/2] bpf: Fix Null-Pointer Dereference in kernel_clone() via BPF fmod_ret on security_task_alloc

[Menglong Dong]

On 2026/4/10 14:10 Feng Yang <yangfeng59949@163.com> write:
> From: Feng Yang <yangfeng@kylinos.cn>
> 
> Using the following BPF program will cause a kernel panic:
> SEC("fmod_ret/security_task_alloc")
> int fmod_task_alloc(void *ctx)
> {
>         return 1;
> }
> 
[...]
> +
> +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;
> +		}

MODIFY_RETURN should always be able to return 0. 0 means
that "not modify the return and call the target function". So
the return value here should not restrict it.

I think it's a limitation of the MODIFY_RETURN, as it can't modify
the return value to 0/false. Maybe we can introduce a kfunc, such
as bpf_set_return_zero(), but it will be complex, as we need do
some adjustment to the trampoline, which I suspect Alexei won't
like it.

However, it's another problem. So, for this patch, I think we need
to make retval_range always cover "0".

BTW, I see you've moved some code upwards, which is not very
friendly for review and will also make the patch relatively large.
I suggest you declare modify_return_get_retval_range and
bpf_security_get_retval_range at the beginning of the file instead.

Thanks!
Menglong Dong

> +		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
> 
> 
> 

[PATCH v2 bpf-next 2/2] selftests/bpf: Add selftests for verifying return values of fmod_ret.

[Feng Yang]

From: Feng Yang <yangfeng@kylinos.cn>

Add selftests for verifying return values of fmod_ret.
test_progs -t verifier_fmod_ret_return
569/1   verifier_fmod_ret_return/fmod_task_alloc_1:OK
569/2   verifier_fmod_ret_return/fmod_task_alloc_2:OK
569/3   verifier_fmod_ret_return/fmod_ret_sys_open_1:OK
569/4   verifier_fmod_ret_return/fmod_ret_sys_open_2:OK
569/5   verifier_fmod_ret_return/fmod_ret_sys_open_3:OK
569/6   verifier_fmod_ret_return/fmod_page_pool_alloc_netmems_1:OK
569/7   verifier_fmod_ret_return/fmod_page_pool_alloc_netmems_2:OK
569     verifier_fmod_ret_return:OK
Summary: 1/7 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
---
 .../selftests/bpf/prog_tests/verifier.c       |  2 +
 .../bpf/progs/verifier_fmod_ret_return.c      | 60 +++++++++++++++++++
 2 files changed, 62 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/verifier_fmod_ret_return.c

diff --git a/tools/testing/selftests/bpf/prog_tests/verifier.c b/tools/testing/selftests/bpf/prog_tests/verifier.c
index 169cf7fbf40f..6e67f69d88fa 100644
--- a/tools/testing/selftests/bpf/prog_tests/verifier.c
+++ b/tools/testing/selftests/bpf/prog_tests/verifier.c
@@ -37,6 +37,7 @@
 #include "verifier_div0.skel.h"
 #include "verifier_div_mod_bounds.skel.h"
 #include "verifier_div_overflow.skel.h"
+#include "verifier_fmod_ret_return.skel.h"
 #include "verifier_global_subprogs.skel.h"
 #include "verifier_global_ptr_args.skel.h"
 #include "verifier_gotol.skel.h"
@@ -184,6 +185,7 @@ void test_verifier_direct_stack_access_wraparound(void) { RUN(verifier_direct_st
 void test_verifier_div0(void)                 { RUN(verifier_div0); }
 void test_verifier_div_mod_bounds(void)       { RUN(verifier_div_mod_bounds); }
 void test_verifier_div_overflow(void)         { RUN(verifier_div_overflow); }
+void test_verifier_fmod_ret_return(void)      { RUN(verifier_fmod_ret_return); }
 void test_verifier_global_subprogs(void)      { RUN(verifier_global_subprogs); }
 void test_verifier_global_ptr_args(void)      { RUN(verifier_global_ptr_args); }
 void test_verifier_gotol(void)                { RUN(verifier_gotol); }
diff --git a/tools/testing/selftests/bpf/progs/verifier_fmod_ret_return.c b/tools/testing/selftests/bpf/progs/verifier_fmod_ret_return.c
new file mode 100644
index 000000000000..11d303b01c80
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/verifier_fmod_ret_return.c
@@ -0,0 +1,60 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bpf.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+
+SEC("fmod_ret/security_task_alloc")
+__success
+int BPF_PROG(fmod_task_alloc_1)
+{
+	return -1;
+}
+
+SEC("fmod_ret/security_task_alloc")
+__failure __log_level(2)
+__msg("At program exit the register R0 has smin=1 smax=1 should have been in [-4095, 0]")
+int BPF_PROG(fmod_task_alloc_2)
+{
+	return 1;
+}
+
+SEC("fmod_ret/" SYS_PREFIX "sys_open")
+__failure __log_level(2)
+__msg("At program exit the register R0 has smin=0 smax=0 should have been in [-4095, -1]")
+int BPF_PROG(fmod_ret_sys_open_1)
+{
+	return 0;
+}
+
+SEC("fmod_ret/" SYS_PREFIX "sys_open")
+__failure __log_level(2)
+__msg("At program exit the register R0 has smin=1 smax=1 should have been in [-4095, -1]")
+int BPF_PROG(fmod_ret_sys_open_2)
+{
+	return 1;
+}
+
+SEC("fmod_ret/" SYS_PREFIX "sys_open")
+__success
+int BPF_PROG(fmod_ret_sys_open_3)
+{
+	return -1;
+}
+
+SEC("fmod_ret/page_pool_alloc_netmems")
+__failure __log_level(2)
+__msg("At program exit the register R0 has smin=1 smax=1 should have been in [0, 0]")
+int BPF_PROG(fmod_page_pool_alloc_netmems_1)
+{
+	return 1;
+}
+
+SEC("fmod_ret/page_pool_alloc_netmems")
+__success
+int BPF_PROG(fmod_page_pool_alloc_netmems_2)
+{
+	return 0;
+}
+
+char _license[] SEC("license") = "GPL";
-- 
2.43.0