[PATCH RFC] LSM: lsm_self_attr system call to get security module attributes

This is probably a tin-man proposal for the first in a series of system calls dealing with Linux security module data. It is based on suggestions by Paul Moore, however the flaws in design and implementation are all mine. Create a system call lsm_self_attr() to provide the security module maintained attributes of the current process. Historically these attributes have been exposed to user space via entries in procfs under /proc/self/attr. Attributes are provided as a collection of lsm_ctx structures which are placed into a user supplied buffer. Each structure identifies the security module providing the attribute, which of the possible attributes is provided, the size of the attribute, and finally the attribute value as a nul terminated string. An LSM ID table is introduced to map IDs to security modules. Signed-off-by: Casey Schaufler <casey(a)schaufler-ca.com&gt; -- arch/x86/entry/syscalls/syscall_64.tbl | 1 + include/linux/syscalls.h | 1 + include/uapi/asm-generic/unistd.h | 5 +- include/uapi/linux/lsm.h | 67 +++++++++++++ kernel/sys_ni.c | 3 + security/Makefile | 2 +- security/lsm_syscalls.c | 166 +++++++++++++++++++++++++++++++++ 7 files changed, 243 insertions(+), 2 deletions(-) diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl index c84d12608cd2..56d5c5202fd0 100644 --- a/arch/x86/entry/syscalls/syscall_64.tbl +++ b/arch/x86/entry/syscalls/syscall_64.tbl @@ -372,6 +372,7 @@ 448 common process_mrelease sys_process_mrelease 449 common futex_waitv sys_futex_waitv 450 common set_mempolicy_home_node sys_set_mempolicy_home_node +451 common lsm_self_attr sys_lsm_self_attr # # Due to a historical design error, certain syscalls are numbered differently diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h index a34b0f9a9972..7f87ef8be546 100644 --- a/include/linux/syscalls.h +++ b/include/linux/syscalls.h @@ -1056,6 +1056,7 @@ asmlinkage long sys_memfd_secret(unsigned int flags); asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len, unsigned long home_node, unsigned long flags); +asmlinkage long sys_lsm_self_attr(struct lsm_ctx *ctx, size_t *size, int flags); /* * Architecture-specific system calls diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h index 45fa180cc56a..aa66718e1b48 100644 --- a/include/uapi/asm-generic/unistd.h +++ b/include/uapi/asm-generic/unistd.h @@ -886,8 +886,11 @@ __SYSCALL(__NR_futex_waitv, sys_futex_waitv) #define __NR_set_mempolicy_home_node 450 __SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node) +#define __NR_lsm_self_attr 451 +__SYSCALL(__NR_lsm_self_attr, sys_lsm_self_attr) + #undef __NR_syscalls -#define __NR_syscalls 451 +#define __NR_syscalls 452 /* * 32 bit systems traditionally used different diff --git a/include/uapi/linux/lsm.h b/include/uapi/linux/lsm.h new file mode 100644 index 000000000000..ec7bb1a7b943 --- /dev/null +++ b/include/uapi/linux/lsm.h @@ -0,0 +1,67 @@ +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */ +/* + * Linus Security Modules (LSM) - User space API + * + * Copyright (C) 2022 Casey Schaufler <casey(a)schaufler-ca.com&gt; + * Copyright (C) Intel Corporation + */ + +#ifndef _UAPI_LINUX_LSM_H +#define _UAPI_LINUX_LSM_H + +#include <linux/types.h> +#include <linux/unistd.h> + +/** + * struct lsm_ctx - LSM context + * @id: the LSM id number, see LSM_ID_XXX + * @flags: context specifier and LSM specific flags + * @ctx_len: the size of @ctx + * @ctx: the LSM context, a nul terminated string + * + * @ctx in a nul terminated string. + * (strlen(@ctx) < @ctx_len) is always true. + * (strlen(@ctx) == @ctx_len + 1) is not guaranteed. + */ +struct lsm_ctx { + unsigned int id; + unsigned int flags; + __kernel_size_t ctx_len; + unsigned char ctx[]; +}; + +/* + * ID values to identify security modules. + * A system may use more than one security module. + * + * LSM_ID_XXX values 32 and below are reserved for future use + */ +#define LSM_ID_SELINUX 33 +#define LSM_ID_SMACK 34 +#define LSM_ID_TOMOYO 35 +#define LSM_ID_IMA 36 +#define LSM_ID_APPARMOR 37 +#define LSM_ID_YAMA 38 +#define LSM_ID_LOADPIN 39 +#define LSM_ID_SAFESETID 40 +#define LSM_ID_LOCKDOWN 41 +#define LSM_ID_BPF 42 +#define LSM_ID_LANDLOCK 43 + +/* + * Flag values. + * + * LSM_ATTR_XXX values identify the /proc/.../attr entry that the + * context represents. Not all security modules provide all of these + * values. Some security modules provide none of them. + */ +/* clang-format off */ +#define LSM_ATTR_CURRENT (1UL << 0) +#define LSM_ATTR_EXEC (1UL << 1) +#define LSM_ATTR_FSCREATE (1UL << 2) +#define LSM_ATTR_KEYCREATE (1UL << 3) +#define LSM_ATTR_PREV (1UL << 4) +#define LSM_ATTR_SOCKCREATE (1UL << 5) +/* clang-format on */ + +#endif /* _UAPI_LINUX_LSM_H */ diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index a492f159624f..c579ffc50454 100644 --- a/kernel/sys_ni.c +++ b/kernel/sys_ni.c @@ -262,6 +262,9 @@ COND_SYSCALL_COMPAT(recvmsg); /* mm/nommu.c, also with MMU */ COND_SYSCALL(mremap); +/* security/lsm_syscalls.c */ +COND_SYSCALL(lsm_attr_self); + /* security/keys/keyctl.c */ COND_SYSCALL(add_key); COND_SYSCALL(request_key); diff --git a/security/Makefile b/security/Makefile index 18121f8f85cd..409c47a25fcf 100644 --- a/security/Makefile +++ b/security/Makefile @@ -6,7 +6,7 @@ obj-$(CONFIG_KEYS) += keys/ # always enable default capabilities -obj-y += commoncap.o +obj-y += commoncap.o lsm_syscalls.o obj-$(CONFIG_MMU) += min_addr.o # Object file lists diff --git a/security/lsm_syscalls.c b/security/lsm_syscalls.c new file mode 100644 index 000000000000..fba8aeea1a10 --- /dev/null +++ b/security/lsm_syscalls.c @@ -0,0 +1,166 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * System calls implementing the Linux Security Module API. + * + * Copyright (C) 2022 Casey Schaufler <casey(a)schaufler-ca.com&gt; + * Copyright (C) Intel Corporation + */ + +#include <asm/current.h> +#include <linux/compiler_types.h> +#include <linux/err.h> +#include <linux/errno.h> +#include <linux/security.h> +#include <linux/stddef.h> +#include <linux/syscalls.h> +#include <linux/types.h> +#include <uapi/linux/lsm.h> + +struct id_map { + char *name; + int id; +}; + +static const struct id_map lsm_attr_names[] = { + { "current", LSM_ATTR_CURRENT, }, + { "exec", LSM_ATTR_EXEC, }, + { "fscreate", LSM_ATTR_FSCREATE, }, + { "keycreate", LSM_ATTR_KEYCREATE, }, + { "prev", LSM_ATTR_PREV, }, + { "sockcreate", LSM_ATTR_SOCKCREATE, }, +}; + +static const struct id_map lsm_names[] = { + { "selinux", LSM_ID_SELINUX, }, + { "smack", LSM_ID_SMACK, }, + { "tomoyo", LSM_ID_TOMOYO, }, + { "ima", LSM_ID_IMA, }, + { "apparmor", LSM_ID_APPARMOR, }, + { "yama", LSM_ID_YAMA, }, + { "loadpin", LSM_ID_LOADPIN, }, + { "safesetid", LSM_ID_SAFESETID, }, + { "lockdown", LSM_ID_LOCKDOWN, }, + { "bpf", LSM_ID_BPF, }, + { "landlock", LSM_ID_LANDLOCK, }, +}; + +/** + * lsm_self_attr - Return current task's security module attributes + * @ctx: the LSM contexts + * @size: size of @ctx, updated on return + * @flags: reserved for future use, must be zero + * + * Returns the calling task's LSM contexts. On success this + * function returns the number of @ctx array elements. This value + * may be zero if there are no LSM contexts assigned. If @size is + * insufficient to contain the return data -E2BIG is returned and + * @size is set to the minimum required size. In all other cases + * a negative value indicating the error is returned. + */ +SYSCALL_DEFINE3(lsm_self_attr, + struct lsm_ctx __user *, ctx, + size_t __user *, size, + int, flags) +{ + struct lsm_ctx *final = NULL; + struct lsm_ctx *interum; + struct lsm_ctx *ip; + void *curr; + char **interum_ctx; + char *cp; + size_t total_size = 0; + int count = 0; + int attr; + int lsm; + int len; + int rc = 0; + int i; + + interum = kzalloc(ARRAY_SIZE(lsm_attr_names) * ARRAY_SIZE(lsm_names) * + sizeof(*interum), GFP_KERNEL); + if (interum == NULL) + return -ENOMEM; + ip = interum; + + interum_ctx = kzalloc(ARRAY_SIZE(lsm_attr_names) * + ARRAY_SIZE(lsm_names) * sizeof(*interum_ctx), + GFP_KERNEL); + if (interum_ctx == NULL) { + kfree(interum); + return -ENOMEM; + } + + for (attr = 0; attr < ARRAY_SIZE(lsm_attr_names); attr++) { + for (lsm = 0; lsm < ARRAY_SIZE(lsm_names); lsm++) { + len = security_getprocattr(current, + lsm_names[lsm].name, + lsm_attr_names[attr].name, + &cp); + if (len <= 0) + continue; + + ip->id = lsm_names[lsm].id; + ip->flags = lsm_attr_names[attr].id; + ip->ctx_len = len; + interum_ctx[count] = cp; + /* + * Security modules have been inconsistent about + * including the \0 terminator in the size. Add + * space for it from an abundance of caution. + * At least one security module adds a \n at the + * end of a context to make it look nicer. Change + * that to a \0 so that user space does't have to + * work around it. Because of this meddling it is + * safe to assume that lsm_ctx.name is terminated + * and that strlen(lsm_ctx.name) < lsm.ctx_len. + */ + total_size += sizeof(*interum) + len + 1; + cp = strnchr(cp, len, '\n'); + if (cp != NULL) + *cp = '\0'; + ip++; + count++; + } + } + + if (count == 0) + goto free_out; + + final = kzalloc(total_size, GFP_KERNEL); + if (final == NULL) { + rc = -ENOMEM; + goto free_out; + } + + curr = final; + ip = interum; + for (i = 0; i < count; i++) { + memcpy(curr, ip, sizeof(*interum)); + curr += sizeof(*interum); + memcpy(curr, interum_ctx[i], ip->ctx_len); + curr += interum[i].ctx_len; + ip++; + } + + if (get_user(len, size)) { + rc = -EFAULT; + goto free_out; + } + if (total_size > len) { + rc = -ERANGE; + goto free_out; + } + if (copy_to_user(ctx, final, total_size) != 0 || + put_user(total_size, size) != 0) + rc = -EFAULT; + else + rc = count; + +free_out: + for (i = 0; i < count; i++) + kfree(interum_ctx[i]); + kfree(interum_ctx); + kfree(interum); + kfree(final); + return rc; +}