[v4,bpf-next,1/2] security: Propagate caller information in bpf hooks

Commit Message

Blaise Boscaccy March 4, 2025, 8:30 p.m. UTC

Certain bpf syscall subcommands are available for usage from both
userspace and the kernel. LSM modules or eBPF gatekeeper programs may
need to take a different course of action depending on whether or not
a BPF syscall originated from the kernel or userspace.

Additionally, some of the bpf_attr struct fields contain pointers to
arbitrary memory. Currently the functionality to determine whether or
not a pointer refers to kernel memory or userspace memory is exposed
to the bpf verifier, but that information is missing from various LSM
hooks.

Here we augment the LSM hooks to provide this data, by simply passing
a boolean flag indicating whether or not the call originated in the
kernel, in any hook that contains a bpf_attr struct that corresponds
to a subcommand that may be called from the kernel.

Signed-off-by: Blaise Boscaccy <[e-mail]>
Acked-by: Song Liu <[e-mail]>
---
 include/linux/lsm_hook_defs.h |  6 +++---
 include/linux/security.h      | 12 ++++++------
 kernel/bpf/syscall.c          | 10 +++++-----
 security/security.c           | 15 +++++++++------
 security/selinux/hooks.c      |  6 +++---
 5 files changed, 26 insertions(+), 23 deletions(-)

Comments

Paul Moore March 5, 2025, 12:46 a.m. UTC | #1

On Tue, Mar 4, 2025 at 3:31 PM Blaise Boscaccy
<[e-mail]> wrote:
>
> Certain bpf syscall subcommands are available for usage from both
> userspace and the kernel. LSM modules or eBPF gatekeeper programs may
> need to take a different course of action depending on whether or not
> a BPF syscall originated from the kernel or userspace.
>
> Additionally, some of the bpf_attr struct fields contain pointers to
> arbitrary memory. Currently the functionality to determine whether or
> not a pointer refers to kernel memory or userspace memory is exposed
> to the bpf verifier, but that information is missing from various LSM
> hooks.
>
> Here we augment the LSM hooks to provide this data, by simply passing
> a boolean flag indicating whether or not the call originated in the
> kernel, in any hook that contains a bpf_attr struct that corresponds
> to a subcommand that may be called from the kernel.
>
> Signed-off-by: Blaise Boscaccy <[e-mail]>
> Acked-by: Song Liu <[e-mail]>
> ---
>  include/linux/lsm_hook_defs.h |  6 +++---
>  include/linux/security.h      | 12 ++++++------
>  kernel/bpf/syscall.c          | 10 +++++-----
>  security/security.c           | 15 +++++++++------
>  security/selinux/hooks.c      |  6 +++---
>  5 files changed, 26 insertions(+), 23 deletions(-)

...

> diff --git a/security/security.c b/security/security.c
> index 143561ebc3e89..38c977091a7fd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -5627,6 +5627,7 @@ int security_audit_rule_match(struct lsm_prop *prop, u32 field, u32 op,
>   * @cmd: command
>   * @attr: bpf attribute
>   * @size: size
> + * @is_kernel: whether or not call originated from kernel

This is really nitpicky so please only make this change if you are
respinning the patchset for another reason (it looks like you may need
to do so for other reasons, so I mentioning it), but please change
"is_kernel" to just "kernel" in all the LSM hooks you're updating so
it is more consistent with the other LSM hook boolean parameter flags.

Regardless of the above, this looks good to me.  My ACK is below in
case the BPF folks want to merge this, but I'm also happy to take this
via the LSM tree once the selftest changes are resolved and ACK'd.

Acked-by: Paul Moore <[e-mail]>

Patch

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index e2f1ce37c41ef..c5f045019456f 100644
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -426,14 +426,14 @@  LSM_HOOK(void, LSM_RET_VOID, audit_rule_free, void *lsmrule)
 #endif /* CONFIG_AUDIT */
 
 #ifdef CONFIG_BPF_SYSCALL
-LSM_HOOK(int, 0, bpf, int cmd, union bpf_attr *attr, unsigned int size)
+LSM_HOOK(int, 0, bpf, int cmd, union bpf_attr *attr, unsigned int size, bool is_kernel)
 LSM_HOOK(int, 0, bpf_map, struct bpf_map *map, fmode_t fmode)
 LSM_HOOK(int, 0, bpf_prog, struct bpf_prog *prog)
 LSM_HOOK(int, 0, bpf_map_create, struct bpf_map *map, union bpf_attr *attr,
-	 struct bpf_token *token)
+	 struct bpf_token *token, bool is_kernel)
 LSM_HOOK(void, LSM_RET_VOID, bpf_map_free, struct bpf_map *map)
 LSM_HOOK(int, 0, bpf_prog_load, struct bpf_prog *prog, union bpf_attr *attr,
-	 struct bpf_token *token)
+	 struct bpf_token *token, bool is_kernel)
 LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free, struct bpf_prog *prog)
 LSM_HOOK(int, 0, bpf_token_create, struct bpf_token *token, union bpf_attr *attr,
 	 const struct path *path)
diff --git a/include/linux/security.h b/include/linux/security.h
index 980b6c207cade..7e3e58030777c 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2249,14 +2249,14 @@  struct bpf_map;
 struct bpf_prog;
 struct bpf_token;
 #ifdef CONFIG_SECURITY
-extern int security_bpf(int cmd, union bpf_attr *attr, unsigned int size);
+extern int security_bpf(int cmd, union bpf_attr *attr, unsigned int size, bool is_kernel);
 extern int security_bpf_map(struct bpf_map *map, fmode_t fmode);
 extern int security_bpf_prog(struct bpf_prog *prog);
 extern int security_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
-				   struct bpf_token *token);
+				   struct bpf_token *token, bool is_kernel);
 extern void security_bpf_map_free(struct bpf_map *map);
 extern int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
-				  struct bpf_token *token);
+				  struct bpf_token *token, bool is_kernel);
 extern void security_bpf_prog_free(struct bpf_prog *prog);
 extern int security_bpf_token_create(struct bpf_token *token, union bpf_attr *attr,
 				     const struct path *path);
@@ -2265,7 +2265,7 @@  extern int security_bpf_token_cmd(const struct bpf_token *token, enum bpf_cmd cm
 extern int security_bpf_token_capable(const struct bpf_token *token, int cap);
 #else
 static inline int security_bpf(int cmd, union bpf_attr *attr,
-					     unsigned int size)
+			       unsigned int size, bool is_kernel)
 {
 	return 0;
 }
@@ -2281,7 +2281,7 @@  static inline int security_bpf_prog(struct bpf_prog *prog)
 }
 
 static inline int security_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
-					  struct bpf_token *token)
+					  struct bpf_token *token, bool is_kernel)
 {
 	return 0;
 }
@@ -2290,7 +2290,7 @@  static inline void security_bpf_map_free(struct bpf_map *map)
 { }
 
 static inline int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
-					 struct bpf_token *token)
+					 struct bpf_token *token, bool is_kernel)
 {
 	return 0;
 }
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 694a675769a60..fc51737b9e3dc 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -1306,7 +1306,7 @@  static bool bpf_net_capable(void)
 
 #define BPF_MAP_CREATE_LAST_FIELD map_token_fd
 /* called via syscall */
-static int map_create(union bpf_attr *attr)
+static int map_create(union bpf_attr *attr, bool is_kernel)
 {
 	const struct bpf_map_ops *ops;
 	struct bpf_token *token = NULL;
@@ -1498,7 +1498,7 @@  static int map_create(union bpf_attr *attr)
 			attr->btf_vmlinux_value_type_id;
 	}
 
-	err = security_bpf_map_create(map, attr, token);
+	err = security_bpf_map_create(map, attr, token, is_kernel);
 	if (err)
 		goto free_map_sec;
 
@@ -2947,7 +2947,7 @@  static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
 	if (err < 0)
 		goto free_prog;
 
-	err = security_bpf_prog_load(prog, attr, token);
+	err = security_bpf_prog_load(prog, attr, token, uattr.is_kernel);
 	if (err)
 		goto free_prog_sec;
 
@@ -5776,13 +5776,13 @@  static int __sys_bpf(enum bpf_cmd cmd, bpfptr_t uattr, unsigned int size)
 	if (copy_from_bpfptr(&attr, uattr, size) != 0)
 		return -EFAULT;
 
-	err = security_bpf(cmd, &attr, size);
+	err = security_bpf(cmd, &attr, size, uattr.is_kernel);
 	if (err < 0)
 		return err;
 
 	switch (cmd) {
 	case BPF_MAP_CREATE:
-		err = map_create(&attr);
+		err = map_create(&attr, uattr.is_kernel);
 		break;
 	case BPF_MAP_LOOKUP_ELEM:
 		err = map_lookup_elem(&attr);
diff --git a/security/security.c b/security/security.c
index 143561ebc3e89..38c977091a7fd 100644
--- a/security/security.c
+++ b/security/security.c
@@ -5627,6 +5627,7 @@  int security_audit_rule_match(struct lsm_prop *prop, u32 field, u32 op,
  * @cmd: command
  * @attr: bpf attribute
  * @size: size
+ * @is_kernel: whether or not call originated from kernel
  *
  * Do a initial check for all bpf syscalls after the attribute is copied into
  * the kernel. The actual security module can implement their own rules to
@@ -5634,9 +5635,9 @@  int security_audit_rule_match(struct lsm_prop *prop, u32 field, u32 op,
  *
  * Return: Returns 0 if permission is granted.
  */
-int security_bpf(int cmd, union bpf_attr *attr, unsigned int size)
+int security_bpf(int cmd, union bpf_attr *attr, unsigned int size, bool is_kernel)
 {
-	return call_int_hook(bpf, cmd, attr, size);
+	return call_int_hook(bpf, cmd, attr, size, is_kernel);
 }
 
 /**
@@ -5673,6 +5674,7 @@  int security_bpf_prog(struct bpf_prog *prog)
  * @map: BPF map object
  * @attr: BPF syscall attributes used to create BPF map
  * @token: BPF token used to grant user access
+ * @is_kernel: whether or not call originated from kernel
  *
  * Do a check when the kernel creates a new BPF map. This is also the
  * point where LSM blob is allocated for LSMs that need them.
@@ -5680,9 +5682,9 @@  int security_bpf_prog(struct bpf_prog *prog)
  * Return: Returns 0 on success, error on failure.
  */
 int security_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
-			    struct bpf_token *token)
+			    struct bpf_token *token, bool is_kernel)
 {
-	return call_int_hook(bpf_map_create, map, attr, token);
+	return call_int_hook(bpf_map_create, map, attr, token, is_kernel);
 }
 
 /**
@@ -5690,6 +5692,7 @@  int security_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
  * @prog: BPF program object
  * @attr: BPF syscall attributes used to create BPF program
  * @token: BPF token used to grant user access to BPF subsystem
+ * @is_kernel: whether or not call originated from kernel
  *
  * Perform an access control check when the kernel loads a BPF program and
  * allocates associated BPF program object. This hook is also responsible for
@@ -5698,9 +5701,9 @@  int security_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
  * Return: Returns 0 on success, error on failure.
  */
 int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
-			   struct bpf_token *token)
+			   struct bpf_token *token, bool is_kernel)
 {
-	return call_int_hook(bpf_prog_load, prog, attr, token);
+	return call_int_hook(bpf_prog_load, prog, attr, token, is_kernel);
 }
 
 /**
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7b867dfec88ba..5a5ce26c51900 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6866,7 +6866,7 @@  static int selinux_ib_alloc_security(void *ib_sec)
 
 #ifdef CONFIG_BPF_SYSCALL
 static int selinux_bpf(int cmd, union bpf_attr *attr,
-				     unsigned int size)
+		       unsigned int size, bool is_kernel)
 {
 	u32 sid = current_sid();
 	int ret;
@@ -6953,7 +6953,7 @@  static int selinux_bpf_prog(struct bpf_prog *prog)
 }
 
 static int selinux_bpf_map_create(struct bpf_map *map, union bpf_attr *attr,
-				  struct bpf_token *token)
+				  struct bpf_token *token, bool is_kernel)
 {
 	struct bpf_security_struct *bpfsec;
 
@@ -6976,7 +6976,7 @@  static void selinux_bpf_map_free(struct bpf_map *map)
 }
 
 static int selinux_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
-				 struct bpf_token *token)
+				 struct bpf_token *token, bool is_kernel)
 {
 	struct bpf_security_struct *bpfsec;