From: Eric Suen Date: Fri, 5 Dec 2025 02:42:59 +0000 (-0800) Subject: selinux: add support for BPF token access control X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=5473a722f782f79f96b4691400d681c01fcacc2f;p=thirdparty%2Flinux.git selinux: add support for BPF token access control BPF token support was introduced to allow a privileged process to delegate limited BPF functionality—such as map creation and program loading—to an unprivileged process: https://lore.kernel.org/linux-security-module/20231130185229.2688956-1-andrii@kernel.org/ This patch adds SELinux support for controlling BPF token access. With this change, SELinux policies can now enforce constraints on BPF token usage based on both the delegating (privileged) process and the recipient (unprivileged) process. Supported operations currently include: - map_create - prog_load High-level workflow: 1. An unprivileged process creates a VFS context via `fsopen()` and obtains a file descriptor. 2. This descriptor is passed to a privileged process, which configures BPF token delegation options and mounts a BPF filesystem. 3. SELinux records the `creator_sid` of the privileged process during mount setup. 4. The unprivileged process then uses this BPF fs mount to create a token and attach it to subsequent BPF syscalls. 5. During verification of `map_create` and `prog_load`, SELinux uses `creator_sid` and the current SID to check policy permissions via: avc_has_perm(creator_sid, current_sid, SECCLASS_BPF, BPF__MAP_CREATE, NULL); The implementation introduces two new permissions: - map_create_as - prog_load_as At token creation time, SELinux verifies that the current process has the appropriate `*_as` permission (depending on the `allowed_cmds` value in the bpf_token) to act on behalf of the `creator_sid`. Example SELinux policy: allow test_bpf_t self:bpf { map_create map_read map_write prog_load prog_run map_create_as prog_load_as }; Additionally, a new policy capability bpf_token_perms is added to ensure backward compatibility. If disabled, previous behavior ((checks based on current process SID)) is preserved. Signed-off-by: Eric Suen Tested-by: Daniel Durning Reviewed-by: Daniel Durning [PM: merge fuzz, subject tweaks, whitespace tweaks, line length tweaks] Signed-off-by: Paul Moore --- diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c index bb9bf848df4ee..c7c19ceeeb2f1 100644 --- a/security/selinux/hooks.c +++ b/security/selinux/hooks.c @@ -737,6 +737,8 @@ static int selinux_set_mnt_opts(struct super_block *sb, goto out; } + sbsec->creator_sid = current_sid(); + if (strcmp(sb->s_type->name, "proc") == 0) sbsec->flags |= SE_SBPROC | SE_SBGENFS; @@ -908,6 +910,8 @@ static int selinux_cmp_sb_context(const struct super_block *oldsb, if (oldroot->sid != newroot->sid) goto mismatch; } + if (old->creator_sid != new->creator_sid) + goto mismatch; return 0; mismatch: pr_warn("SELinux: mount invalid. Same superblock, " @@ -967,6 +971,7 @@ static int selinux_sb_clone_mnt_opts(const struct super_block *oldsb, newsbsec->sid = oldsbsec->sid; newsbsec->def_sid = oldsbsec->def_sid; newsbsec->behavior = oldsbsec->behavior; + newsbsec->creator_sid = oldsbsec->creator_sid; if (newsbsec->behavior == SECURITY_FS_USE_NATIVE && !(kern_flags & SECURITY_LSM_NATIVE_LABELS) && !set_context) { @@ -2586,6 +2591,7 @@ static int selinux_sb_alloc_security(struct super_block *sb) sbsec->sid = SECINITSID_UNLABELED; sbsec->def_sid = SECINITSID_FILE; sbsec->mntpoint_sid = SECINITSID_UNLABELED; + sbsec->creator_sid = SECINITSID_UNLABELED; return 0; } @@ -7043,6 +7049,9 @@ static int selinux_bpf(int cmd, union bpf_attr *attr, u32 sid = current_sid(); int ret; + if (selinux_policycap_bpf_token_perms()) + return 0; + switch (cmd) { case BPF_MAP_CREATE: ret = avc_has_perm(sid, sid, SECCLASS_BPF, BPF__MAP_CREATE, @@ -7124,38 +7133,143 @@ static int selinux_bpf_prog(struct bpf_prog *prog) BPF__PROG_RUN, NULL); } +static u32 selinux_bpffs_creator_sid(u32 fd) +{ + struct path path; + struct super_block *sb; + struct superblock_security_struct *sbsec; + + CLASS(fd, f)(fd); + + if (fd_empty(f)) + return SECSID_NULL; + + path = fd_file(f)->f_path; + sb = path.dentry->d_sb; + sbsec = selinux_superblock(sb); + + return sbsec->creator_sid; +} + static int selinux_bpf_map_create(struct bpf_map *map, union bpf_attr *attr, struct bpf_token *token, bool kernel) { struct bpf_security_struct *bpfsec; + u32 ssid; bpfsec = selinux_bpf_map_security(map); bpfsec->sid = current_sid(); - return 0; + if (!token) + ssid = bpfsec->sid; + else + ssid = selinux_bpffs_creator_sid(attr->map_token_fd); + + return avc_has_perm(ssid, bpfsec->sid, SECCLASS_BPF, BPF__MAP_CREATE, + NULL); } static int selinux_bpf_prog_load(struct bpf_prog *prog, union bpf_attr *attr, struct bpf_token *token, bool kernel) { struct bpf_security_struct *bpfsec; + u32 ssid; bpfsec = selinux_bpf_prog_security(prog); bpfsec->sid = current_sid(); - return 0; + if (!token) + ssid = bpfsec->sid; + else + ssid = selinux_bpffs_creator_sid(attr->prog_token_fd); + + return avc_has_perm(ssid, bpfsec->sid, SECCLASS_BPF, BPF__PROG_LOAD, + NULL); } -static int selinux_bpf_token_create(struct bpf_token *token, union bpf_attr *attr, +#define bpf_token_cmd(T, C) \ + ((T)->allowed_cmds & (1ULL << (C))) + +static int selinux_bpf_token_create(struct bpf_token *token, + union bpf_attr *attr, const struct path *path) { struct bpf_security_struct *bpfsec; + u32 sid = selinux_bpffs_creator_sid(attr->token_create.bpffs_fd); + int err; bpfsec = selinux_bpf_token_security(token); bpfsec->sid = current_sid(); + bpfsec->grantor_sid = sid; + + bpfsec->perms = 0; + /** + * 'token->allowed_cmds' is a bit mask of allowed commands + * Convert the BPF command enum to a bitmask representing its position + * in the allowed_cmds bitmap. + */ + if (bpf_token_cmd(token, BPF_MAP_CREATE)) { + err = avc_has_perm(bpfsec->sid, sid, SECCLASS_BPF, + BPF__MAP_CREATE_AS, NULL); + if (err) + return err; + bpfsec->perms |= BPF__MAP_CREATE; + } + if (bpf_token_cmd(token, BPF_PROG_LOAD)) { + err = avc_has_perm(bpfsec->sid, sid, SECCLASS_BPF, + BPF__PROG_LOAD_AS, NULL); + if (err) + return err; + bpfsec->perms |= BPF__PROG_LOAD; + } + + return 0; +} + +static int selinux_bpf_token_cmd(const struct bpf_token *token, + enum bpf_cmd cmd) +{ + struct bpf_security_struct *bpfsec; + + bpfsec = token->security; + switch (cmd) { + case BPF_MAP_CREATE: + if (!(bpfsec->perms & BPF__MAP_CREATE)) + return -EACCES; + break; + case BPF_PROG_LOAD: + if (!(bpfsec->perms & BPF__PROG_LOAD)) + return -EACCES; + break; + default: + break; + } return 0; } + +static int selinux_bpf_token_capable(const struct bpf_token *token, int cap) +{ + u16 sclass; + struct bpf_security_struct *bpfsec = token->security; + bool initns = (token->userns == &init_user_ns); + u32 av = CAP_TO_MASK(cap); + + switch (CAP_TO_INDEX(cap)) { + case 0: + sclass = initns ? SECCLASS_CAPABILITY : SECCLASS_CAP_USERNS; + break; + case 1: + sclass = initns ? SECCLASS_CAPABILITY : SECCLASS_CAP2_USERNS; + break; + default: + pr_err("SELinux: out of range capability %d\n", cap); + return -EINVAL; + } + + return avc_has_perm(current_sid(), bpfsec->grantor_sid, sclass, av, + NULL); +} #endif #ifdef CONFIG_PERF_EVENTS @@ -7590,6 +7704,8 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = { LSM_HOOK_INIT(bpf_map_create, selinux_bpf_map_create), LSM_HOOK_INIT(bpf_prog_load, selinux_bpf_prog_load), LSM_HOOK_INIT(bpf_token_create, selinux_bpf_token_create), + LSM_HOOK_INIT(bpf_token_cmd, selinux_bpf_token_cmd), + LSM_HOOK_INIT(bpf_token_capable, selinux_bpf_token_capable), #endif #ifdef CONFIG_PERF_EVENTS LSM_HOOK_INIT(perf_event_alloc, selinux_perf_event_alloc), diff --git a/security/selinux/include/classmap.h b/security/selinux/include/classmap.h index 3ec85142771fc..90cb61b164256 100644 --- a/security/selinux/include/classmap.h +++ b/security/selinux/include/classmap.h @@ -171,7 +171,7 @@ const struct security_class_mapping secclass_map[] = { { "infiniband_endport", { "manage_subnet", NULL } }, { "bpf", { "map_create", "map_read", "map_write", "prog_load", "prog_run", - NULL } }, + "map_create_as", "prog_load_as", NULL } }, { "xdp_socket", { COMMON_SOCK_PERMS, NULL } }, { "mctp_socket", { COMMON_SOCK_PERMS, NULL } }, { "perf_event", diff --git a/security/selinux/include/objsec.h b/security/selinux/include/objsec.h index 8fc3de5234acd..5bddd28ea5cb8 100644 --- a/security/selinux/include/objsec.h +++ b/security/selinux/include/objsec.h @@ -92,6 +92,7 @@ struct superblock_security_struct { u32 sid; /* SID of file system superblock */ u32 def_sid; /* default SID for labeling */ u32 mntpoint_sid; /* SECURITY_FS_USE_MNTPOINT context for files */ + u32 creator_sid; /* SID of privileged process */ unsigned short behavior; /* labeling behavior */ unsigned short flags; /* which mount options were specified */ struct mutex lock; @@ -169,6 +170,8 @@ struct pkey_security_struct { struct bpf_security_struct { u32 sid; /* SID of bpf obj creator */ + u32 perms; /* permissions for allowed bpf token commands */ + u32 grantor_sid; /* SID of token grantor */ }; struct perf_event_security_struct { diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h index 231d02227e593..dbf39358ae6af 100644 --- a/security/selinux/include/policycap.h +++ b/security/selinux/include/policycap.h @@ -19,6 +19,7 @@ enum { POLICYDB_CAP_GENFS_SECLABEL_WILDCARD, POLICYDB_CAP_FUNCTIONFS_SECLABEL, POLICYDB_CAP_MEMFD_CLASS, + POLICYDB_CAP_BPF_TOKEN_PERMS, __POLICYDB_CAP_MAX }; #define POLICYDB_CAP_MAX (__POLICYDB_CAP_MAX - 1) diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h index 454dab37bda3f..6e2b808e12e89 100644 --- a/security/selinux/include/policycap_names.h +++ b/security/selinux/include/policycap_names.h @@ -22,6 +22,7 @@ const char *const selinux_policycap_names[__POLICYDB_CAP_MAX] = { "genfs_seclabel_wildcard", "functionfs_seclabel", "memfd_class", + "bpf_token_perms", }; /* clang-format on */ diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h index 5d1dad8058b14..d1f16d7f684de 100644 --- a/security/selinux/include/security.h +++ b/security/selinux/include/security.h @@ -214,6 +214,12 @@ static inline bool selinux_policycap_memfd_class(void) return READ_ONCE(selinux_state.policycap[POLICYDB_CAP_MEMFD_CLASS]); } +static inline bool selinux_policycap_bpf_token_perms(void) +{ + return READ_ONCE( + selinux_state.policycap[POLICYDB_CAP_BPF_TOKEN_PERMS]); +} + struct selinux_policy_convert_data; struct selinux_load_state {