bpf,lsm: refactor bpf_prog_alloc/bpf_prog_free LSM hooks

Based on upstream discussion ([0]), rework existing
bpf_prog_alloc_security LSM hook. Rename it to bpf_prog_load and instead
of passing bpf_prog_aux, pass proper bpf_prog pointer for a full BPF
program struct. Also, we pass bpf_attr union with all the user-provided
arguments for BPF_PROG_LOAD command.  This will give LSMs as much
information as we can basically provide.

The hook is also BPF token-aware now, and optional bpf_token struct is
passed as a third argument. bpf_prog_load LSM hook is called after
a bunch of sanity checks were performed, bpf_prog and bpf_prog_aux were
allocated and filled out, but right before performing full-fledged BPF
verification step.

bpf_prog_free LSM hook is now accepting struct bpf_prog argument, for
consistency. SELinux code is adjusted to all new names, types, and
signatures.

Note, given that bpf_prog_load (previously bpf_prog_alloc) hook can be
used by some LSMs to allocate extra security blob, but also by other
LSMs to reject BPF program loading, we need to make sure that
bpf_prog_free LSM hook is called after bpf_prog_load/bpf_prog_alloc one
*even* if the hook itself returned error. If we don't do that, we run
the risk of leaking memory. This seems to be possible today when
combining SELinux and BPF LSM, as one example, depending on their
relative ordering.

Also, for BPF LSM setup, add bpf_prog_load and bpf_prog_free to
sleepable LSM hooks list, as they are both executed in sleepable
context. Also drop bpf_prog_load hook from untrusted, as there is no
issue with refcount or anything else anymore, that originally forced us
to add it to untrusted list in c0c852dd1876 ("bpf: Do not mark certain LSM
hook arguments as trusted"). We now trigger this hook much later and it
should not be an issue anymore.

  [0] https://lore.kernel.org/bpf/9fe88aef7deabbe87d3fc38c4aea3c69.paul@paul-moore.com/

Acked-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20231130185229.2688956-10-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

diff --git a/include/linux/lsm_hook_defs.h b/include/linux/lsm_hook_defs.h
index ff217a5ce552143e39717acc4a25ed9c8109fe7b..41ec4a7c070e256c437da4d793c763fa0219eed7 100644 (file)
--- a/include/linux/lsm_hook_defs.h
+++ b/include/linux/lsm_hook_defs.h
@@ -400,8 +400,9 @@ 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_alloc_security, struct bpf_map *map)
 LSM_HOOK(void, LSM_RET_VOID, bpf_map_free_security, struct bpf_map *map)
-LSM_HOOK(int, 0, bpf_prog_alloc_security, struct bpf_prog_aux *aux)
-LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free_security, struct bpf_prog_aux *aux)
+LSM_HOOK(int, 0, bpf_prog_load, struct bpf_prog *prog, union bpf_attr *attr,
+        struct bpf_token *token)
+LSM_HOOK(void, LSM_RET_VOID, bpf_prog_free, struct bpf_prog *prog)
 #endif /* CONFIG_BPF_SYSCALL */
 
 LSM_HOOK(int, 0, locked_down, enum lockdown_reason what)

diff --git a/include/linux/security.h b/include/linux/security.h
index 1d1df326c881c7e1a97d748066d046590c4aea72..65467eef6678c2c6db25d79d35e8550df9351949 100644 (file)
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -2020,15 +2020,16 @@ static inline void securityfs_remove(struct dentry *dentry)
 union bpf_attr;
 struct bpf_map;
 struct bpf_prog;
-struct bpf_prog_aux;
+struct bpf_token;
 #ifdef CONFIG_SECURITY
 extern int security_bpf(int cmd, union bpf_attr *attr, unsigned int size);
 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_alloc(struct bpf_map *map);
 extern void security_bpf_map_free(struct bpf_map *map);
-extern int security_bpf_prog_alloc(struct bpf_prog_aux *aux);
-extern void security_bpf_prog_free(struct bpf_prog_aux *aux);
+extern int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
+                                 struct bpf_token *token);
+extern void security_bpf_prog_free(struct bpf_prog *prog);
 #else
 static inline int security_bpf(int cmd, union bpf_attr *attr,
                                             unsigned int size)
@@ -2054,12 +2055,13 @@ static inline int security_bpf_map_alloc(struct bpf_map *map)
 static inline void security_bpf_map_free(struct bpf_map *map)
 { }
 
-static inline int security_bpf_prog_alloc(struct bpf_prog_aux *aux)
+static inline int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
+                                        struct bpf_token *token)
 {
        return 0;
 }
 
-static inline void security_bpf_prog_free(struct bpf_prog_aux *aux)
+static inline void security_bpf_prog_free(struct bpf_prog *prog)
 { }
 #endif /* CONFIG_SECURITY */
 #endif /* CONFIG_BPF_SYSCALL */

diff --git a/kernel/bpf/bpf_lsm.c b/kernel/bpf/bpf_lsm.c
index e14c822f8911c9699ff0159fd51ad8bcc6ad31e5..3e956f6302f3576b55050626f33478c3347b700c 100644 (file)
--- a/kernel/bpf/bpf_lsm.c
+++ b/kernel/bpf/bpf_lsm.c
@@ -263,6 +263,8 @@ BTF_ID(func, bpf_lsm_bpf_map)
 BTF_ID(func, bpf_lsm_bpf_map_alloc_security)
 BTF_ID(func, bpf_lsm_bpf_map_free_security)
 BTF_ID(func, bpf_lsm_bpf_prog)
+BTF_ID(func, bpf_lsm_bpf_prog_load)
+BTF_ID(func, bpf_lsm_bpf_prog_free)
 BTF_ID(func, bpf_lsm_bprm_check_security)
 BTF_ID(func, bpf_lsm_bprm_committed_creds)
 BTF_ID(func, bpf_lsm_bprm_committing_creds)
@@ -346,8 +348,7 @@ BTF_SET_END(sleepable_lsm_hooks)
 
 BTF_SET_START(untrusted_lsm_hooks)
 BTF_ID(func, bpf_lsm_bpf_map_free_security)
-BTF_ID(func, bpf_lsm_bpf_prog_alloc_security)
-BTF_ID(func, bpf_lsm_bpf_prog_free_security)
+BTF_ID(func, bpf_lsm_bpf_prog_free)
 BTF_ID(func, bpf_lsm_file_alloc_security)
 BTF_ID(func, bpf_lsm_file_free_security)
 #ifdef CONFIG_SECURITY_NETWORK

diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 1cc03f08c9cd22b7474217383024b35c82896263..7717c7c7b95d56358ab749bf4bbb7d56c50ab57d 100644 (file)
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -2162,7 +2162,7 @@ static void __bpf_prog_put_rcu(struct rcu_head *rcu)
        kvfree(aux->func_info);
        kfree(aux->func_info_aux);
        free_uid(aux->user);
-       security_bpf_prog_free(aux);
+       security_bpf_prog_free(aux->prog);
        bpf_prog_free(aux->prog);
 }
 
@@ -2753,10 +2753,6 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
        prog->aux->token = token;
        token = NULL;
 
-       err = security_bpf_prog_alloc(prog->aux);
-       if (err)
-               goto free_prog;
-
        prog->aux->user = get_current_user();
        prog->len = attr->insn_cnt;
 
@@ -2764,12 +2760,12 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
        if (copy_from_bpfptr(prog->insns,
                             make_bpfptr(attr->insns, uattr.is_kernel),
                             bpf_prog_insn_size(prog)) != 0)
-               goto free_prog_sec;
+               goto free_prog;
        /* copy eBPF program license from user space */
        if (strncpy_from_bpfptr(license,
                                make_bpfptr(attr->license, uattr.is_kernel),
                                sizeof(license) - 1) < 0)
-               goto free_prog_sec;
+               goto free_prog;
        license[sizeof(license) - 1] = 0;
 
        /* eBPF programs must be GPL compatible to use GPL-ed functions */
@@ -2783,25 +2779,29 @@ static int bpf_prog_load(union bpf_attr *attr, bpfptr_t uattr, u32 uattr_size)
        if (bpf_prog_is_dev_bound(prog->aux)) {
                err = bpf_prog_dev_bound_init(prog, attr);
                if (err)
-                       goto free_prog_sec;
+                       goto free_prog;
        }
 
        if (type == BPF_PROG_TYPE_EXT && dst_prog &&
            bpf_prog_is_dev_bound(dst_prog->aux)) {
                err = bpf_prog_dev_bound_inherit(prog, dst_prog);
                if (err)
-                       goto free_prog_sec;
+                       goto free_prog;
        }
 
        /* find program type: socket_filter vs tracing_filter */
        err = find_prog_type(type, prog);
        if (err < 0)
-               goto free_prog_sec;
+               goto free_prog;
 
        prog->aux->load_time = ktime_get_boottime_ns();
        err = bpf_obj_name_cpy(prog->aux->name, attr->prog_name,
                               sizeof(attr->prog_name));
        if (err < 0)
+               goto free_prog;
+
+       err = security_bpf_prog_load(prog, attr, token);
+       if (err)
                goto free_prog_sec;
 
        /* run eBPF verifier */
@@ -2847,10 +2847,11 @@ free_used_maps:
         */
        __bpf_prog_put_noref(prog, prog->aux->real_func_cnt);
        return err;
+
 free_prog_sec:
-       free_uid(prog->aux->user);
-       security_bpf_prog_free(prog->aux);
+       security_bpf_prog_free(prog);
 free_prog:
+       free_uid(prog->aux->user);
        if (prog->aux->attach_btf)
                btf_put(prog->aux->attach_btf);
        bpf_prog_free(prog);

diff --git a/security/security.c b/security/security.c
index dcb3e7014f9bdd4b6115f0407c5b1d7d3a588e9c..c8a1c66cfaadd245247e385c24a9e46ae5e831df 100644 (file)
--- a/security/security.c
+++ b/security/security.c
@@ -5180,16 +5180,21 @@ int security_bpf_map_alloc(struct bpf_map *map)
 }
 
 /**
- * security_bpf_prog_alloc() - Allocate a bpf program LSM blob
- * @aux: bpf program aux info struct
+ * security_bpf_prog_load() - Check if loading of BPF program is allowed
+ * @prog: BPF program object
+ * @attr: BPF syscall attributes used to create BPF program
+ * @token: BPF token used to grant user access to BPF subsystem
  *
- * Initialize the security field inside bpf program.
+ * Perform an access control check when the kernel loads a BPF program and
+ * allocates associated BPF program object. This hook is also responsible for
+ * allocating any required LSM state for the BPF program.
  *
  * Return: Returns 0 on success, error on failure.
  */
-int security_bpf_prog_alloc(struct bpf_prog_aux *aux)
+int security_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
+                          struct bpf_token *token)
 {
-       return call_int_hook(bpf_prog_alloc_security, 0, aux);
+       return call_int_hook(bpf_prog_load, 0, prog, attr, token);
 }
 
 /**
@@ -5204,14 +5209,14 @@ void security_bpf_map_free(struct bpf_map *map)
 }
 
 /**
- * security_bpf_prog_free() - Free a bpf program's LSM blob
- * @aux: bpf program aux info struct
+ * security_bpf_prog_free() - Free a BPF program's LSM blob
+ * @prog: BPF program struct
  *
- * Clean up the security information stored inside bpf prog.
+ * Clean up the security information stored inside BPF program.
  */
-void security_bpf_prog_free(struct bpf_prog_aux *aux)
+void security_bpf_prog_free(struct bpf_prog *prog)
 {
-       call_void_hook(bpf_prog_free_security, aux);
+       call_void_hook(bpf_prog_free, prog);
 }
 #endif /* CONFIG_BPF_SYSCALL */
 

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index feda711c6b7b84c19099568b96b3b5cbf121886d..eabee39e983c52b5d9fbfc4d4ee557ca6c0ed023 100644 (file)
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6805,7 +6805,8 @@ static void selinux_bpf_map_free(struct bpf_map *map)
        kfree(bpfsec);
 }
 
-static int selinux_bpf_prog_alloc(struct bpf_prog_aux *aux)
+static int selinux_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr,
+                                struct bpf_token *token)
 {
        struct bpf_security_struct *bpfsec;
 
@@ -6814,16 +6815,16 @@ static int selinux_bpf_prog_alloc(struct bpf_prog_aux *aux)
                return -ENOMEM;
 
        bpfsec->sid = current_sid();
-       aux->security = bpfsec;
+       prog->aux->security = bpfsec;
 
        return 0;
 }
 
-static void selinux_bpf_prog_free(struct bpf_prog_aux *aux)
+static void selinux_bpf_prog_free(struct bpf_prog *prog)
 {
-       struct bpf_security_struct *bpfsec = aux->security;
+       struct bpf_security_struct *bpfsec = prog->aux->security;
 
-       aux->security = NULL;
+       prog->aux->security = NULL;
        kfree(bpfsec);
 }
 #endif
@@ -7180,7 +7181,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
        LSM_HOOK_INIT(bpf_map, selinux_bpf_map),
        LSM_HOOK_INIT(bpf_prog, selinux_bpf_prog),
        LSM_HOOK_INIT(bpf_map_free_security, selinux_bpf_map_free),
-       LSM_HOOK_INIT(bpf_prog_free_security, selinux_bpf_prog_free),
+       LSM_HOOK_INIT(bpf_prog_free, selinux_bpf_prog_free),
 #endif
 
 #ifdef CONFIG_PERF_EVENTS
@@ -7238,7 +7239,7 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 #endif
 #ifdef CONFIG_BPF_SYSCALL
        LSM_HOOK_INIT(bpf_map_alloc_security, selinux_bpf_map_alloc),
-       LSM_HOOK_INIT(bpf_prog_alloc_security, selinux_bpf_prog_alloc),
+       LSM_HOOK_INIT(bpf_prog_load, selinux_bpf_prog_load),
 #endif
 #ifdef CONFIG_PERF_EVENTS
        LSM_HOOK_INIT(perf_event_alloc, selinux_perf_event_alloc),