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@xxxxxxxxxxxxxxxx>
--
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@xxxxxxxxxxxxxxxx>
+ * 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@xxxxxxxxxxxxxxxx>
+ * 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;
+}
