Commit 2813893f authored by Iulia Manda's avatar Iulia Manda Committed by Linus Torvalds

kernel: conditionally support non-root users, groups and capabilities

There are a lot of embedded systems that run most or all of their
functionality in init, running as root:root.  For these systems,
supporting multiple users is not necessary.

This patch adds a new symbol, CONFIG_MULTIUSER, that makes support for
non-root users, non-root groups, and capabilities optional.  It is enabled
under CONFIG_EXPERT menu.

When this symbol is not defined, UID and GID are zero in any possible case
and processes always have all capabilities.

The following syscalls are compiled out: setuid, setregid, setgid,
setreuid, setresuid, getresuid, setresgid, getresgid, setgroups,
getgroups, setfsuid, setfsgid, capget, capset.

Also, groups.c is compiled out completely.

In kernel/capability.c, capable function was moved in order to avoid
adding two ifdef blocks.

This change saves about 25 KB on a defconfig build.  The most minimal
kernels have total text sizes in the high hundreds of kB rather than
low MB.  (The 25k goes down a bit with allnoconfig, but not that much.

The kernel was booted in Qemu.  All the common functionalities work.
Adding users/groups is not possible, failing with -ENOSYS.

Bloat-o-meter output:
add/remove: 7/87 grow/shrink: 19/397 up/down: 1675/-26325 (-24650)

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: default avatarIulia Manda <iulia.manda21@gmail.com>
Reviewed-by: default avatarJosh Triplett <josh@joshtriplett.org>
Acked-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
Tested-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c79574ab
......@@ -328,6 +328,7 @@ config COMPAT
select COMPAT_BINFMT_ELF if BINFMT_ELF
select ARCH_WANT_OLD_COMPAT_IPC
select COMPAT_OLD_SIGACTION
depends on MULTIUSER
help
Select this option if you want to enable your system kernel to
handle system-calls from ELF binaries for 31 bit ESA. This option
......
......@@ -10,6 +10,7 @@ config LUSTRE_FS
select CRYPTO_SHA1
select CRYPTO_SHA256
select CRYPTO_SHA512
depends on MULTIUSER
help
This option enables Lustre file system client support. Choose Y
here if you want to access a Lustre file system cluster. To compile
......
config NFS_FS
tristate "NFS client support"
depends on INET && FILE_LOCKING
depends on INET && FILE_LOCKING && MULTIUSER
select LOCKD
select SUNRPC
select NFS_ACL_SUPPORT if NFS_V3_ACL
......
......@@ -6,6 +6,7 @@ config NFSD
select SUNRPC
select EXPORTFS
select NFS_ACL_SUPPORT if NFSD_V2_ACL
depends on MULTIUSER
help
Choose Y here if you want to allow other computers to access
files residing on this system using Sun's Network File System
......
......@@ -205,6 +205,7 @@ static inline kernel_cap_t cap_raise_nfsd_set(const kernel_cap_t a,
cap_intersect(permitted, __cap_nfsd_set));
}
#ifdef CONFIG_MULTIUSER
extern bool has_capability(struct task_struct *t, int cap);
extern bool has_ns_capability(struct task_struct *t,
struct user_namespace *ns, int cap);
......@@ -213,6 +214,34 @@ extern bool has_ns_capability_noaudit(struct task_struct *t,
struct user_namespace *ns, int cap);
extern bool capable(int cap);
extern bool ns_capable(struct user_namespace *ns, int cap);
#else
static inline bool has_capability(struct task_struct *t, int cap)
{
return true;
}
static inline bool has_ns_capability(struct task_struct *t,
struct user_namespace *ns, int cap)
{
return true;
}
static inline bool has_capability_noaudit(struct task_struct *t, int cap)
{
return true;
}
static inline bool has_ns_capability_noaudit(struct task_struct *t,
struct user_namespace *ns, int cap)
{
return true;
}
static inline bool capable(int cap)
{
return true;
}
static inline bool ns_capable(struct user_namespace *ns, int cap)
{
return true;
}
#endif /* CONFIG_MULTIUSER */
extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
......
......@@ -62,9 +62,27 @@ do { \
groups_free(group_info); \
} while (0)
extern struct group_info *groups_alloc(int);
extern struct group_info init_groups;
#ifdef CONFIG_MULTIUSER
extern struct group_info *groups_alloc(int);
extern void groups_free(struct group_info *);
extern int in_group_p(kgid_t);
extern int in_egroup_p(kgid_t);
#else
static inline void groups_free(struct group_info *group_info)
{
}
static inline int in_group_p(kgid_t grp)
{
return 1;
}
static inline int in_egroup_p(kgid_t grp)
{
return 1;
}
#endif
extern int set_current_groups(struct group_info *);
extern void set_groups(struct cred *, struct group_info *);
extern int groups_search(const struct group_info *, kgid_t);
......@@ -74,9 +92,6 @@ extern bool may_setgroups(void);
#define GROUP_AT(gi, i) \
((gi)->blocks[(i) / NGROUPS_PER_BLOCK][(i) % NGROUPS_PER_BLOCK])
extern int in_group_p(kgid_t);
extern int in_egroup_p(kgid_t);
/*
* The security context of a task
*
......
......@@ -29,6 +29,7 @@ typedef struct {
#define KUIDT_INIT(value) (kuid_t){ value }
#define KGIDT_INIT(value) (kgid_t){ value }
#ifdef CONFIG_MULTIUSER
static inline uid_t __kuid_val(kuid_t uid)
{
return uid.val;
......@@ -38,6 +39,17 @@ static inline gid_t __kgid_val(kgid_t gid)
{
return gid.val;
}
#else
static inline uid_t __kuid_val(kuid_t uid)
{
return 0;
}
static inline gid_t __kgid_val(kgid_t gid)
{
return 0;
}
#endif
#define GLOBAL_ROOT_UID KUIDT_INIT(0)
#define GLOBAL_ROOT_GID KGIDT_INIT(0)
......
......@@ -394,6 +394,7 @@ endchoice
config BSD_PROCESS_ACCT
bool "BSD Process Accounting"
depends on MULTIUSER
help
If you say Y here, a user level program will be able to instruct the
kernel (via a special system call) to write process accounting
......@@ -420,6 +421,7 @@ config BSD_PROCESS_ACCT_V3
config TASKSTATS
bool "Export task/process statistics through netlink"
depends on NET
depends on MULTIUSER
default n
help
Export selected statistics for tasks/processes through the
......@@ -1160,6 +1162,7 @@ config CHECKPOINT_RESTORE
menuconfig NAMESPACES
bool "Namespaces support" if EXPERT
depends on MULTIUSER
default !EXPERT
help
Provides the way to make tasks work with different objects using
......@@ -1356,11 +1359,25 @@ menuconfig EXPERT
config UID16
bool "Enable 16-bit UID system calls" if EXPERT
depends on HAVE_UID16
depends on HAVE_UID16 && MULTIUSER
default y
help
This enables the legacy 16-bit UID syscall wrappers.
config MULTIUSER
bool "Multiple users, groups and capabilities support" if EXPERT
default y
help
This option enables support for non-root users, groups and
capabilities.
If you say N here, all processes will run with UID 0, GID 0, and all
possible capabilities. Saying N here also compiles out support for
system calls related to UIDs, GIDs, and capabilities, such as setuid,
setgid, and capset.
If unsure, say Y here.
config SGETMASK_SYSCALL
bool "sgetmask/ssetmask syscalls support" if EXPERT
def_bool PARISC || MN10300 || BLACKFIN || M68K || PPC || MIPS || X86 || SPARC || CRIS || MICROBLAZE || SUPERH
......
......@@ -9,7 +9,9 @@ obj-y = fork.o exec_domain.o panic.o \
extable.o params.o \
kthread.o sys_ni.o nsproxy.o \
notifier.o ksysfs.o cred.o reboot.o \
async.o range.o groups.o smpboot.o
async.o range.o smpboot.o
obj-$(CONFIG_MULTIUSER) += groups.o
ifdef CONFIG_FUNCTION_TRACER
# Do not trace debug files and internal ftrace files
......
......@@ -35,6 +35,7 @@ static int __init file_caps_disable(char *str)
}
__setup("no_file_caps", file_caps_disable);
#ifdef CONFIG_MULTIUSER
/*
* More recent versions of libcap are available from:
*
......@@ -386,6 +387,24 @@ bool ns_capable(struct user_namespace *ns, int cap)
}
EXPORT_SYMBOL(ns_capable);
/**
* capable - Determine if the current task has a superior capability in effect
* @cap: The capability to be tested for
*
* Return true if the current task has the given superior capability currently
* available for use, false if not.
*
* This sets PF_SUPERPRIV on the task if the capability is available on the
* assumption that it's about to be used.
*/
bool capable(int cap)
{
return ns_capable(&init_user_ns, cap);
}
EXPORT_SYMBOL(capable);
#endif /* CONFIG_MULTIUSER */
/**
* file_ns_capable - Determine if the file's opener had a capability in effect
* @file: The file we want to check
......@@ -411,22 +430,6 @@ bool file_ns_capable(const struct file *file, struct user_namespace *ns,
}
EXPORT_SYMBOL(file_ns_capable);
/**
* capable - Determine if the current task has a superior capability in effect
* @cap: The capability to be tested for
*
* Return true if the current task has the given superior capability currently
* available for use, false if not.
*
* This sets PF_SUPERPRIV on the task if the capability is available on the
* assumption that it's about to be used.
*/
bool capable(int cap)
{
return ns_capable(&init_user_ns, cap);
}
EXPORT_SYMBOL(capable);
/**
* capable_wrt_inode_uidgid - Check nsown_capable and uid and gid mapped
* @inode: The inode in question
......
......@@ -29,6 +29,9 @@
static struct kmem_cache *cred_jar;
/* init to 2 - one for init_task, one to ensure it is never freed */
struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
/*
* The initial credentials for the initial task
*/
......
......@@ -9,9 +9,6 @@
#include <linux/user_namespace.h>
#include <asm/uaccess.h>
/* init to 2 - one for init_task, one to ensure it is never freed */
struct group_info init_groups = { .usage = ATOMIC_INIT(2) };
struct group_info *groups_alloc(int gidsetsize)
{
struct group_info *group_info;
......
......@@ -325,6 +325,7 @@ out_unlock:
* SMP: There are not races, the GIDs are checked only by filesystem
* operations (as far as semantic preservation is concerned).
*/
#ifdef CONFIG_MULTIUSER
SYSCALL_DEFINE2(setregid, gid_t, rgid, gid_t, egid)
{
struct user_namespace *ns = current_user_ns();
......@@ -815,6 +816,7 @@ change_okay:
commit_creds(new);
return old_fsgid;
}
#endif /* CONFIG_MULTIUSER */
/**
* sys_getpid - return the thread group id of the current process
......
......@@ -159,6 +159,20 @@ cond_syscall(sys_uselib);
cond_syscall(sys_fadvise64);
cond_syscall(sys_fadvise64_64);
cond_syscall(sys_madvise);
cond_syscall(sys_setuid);
cond_syscall(sys_setregid);
cond_syscall(sys_setgid);
cond_syscall(sys_setreuid);
cond_syscall(sys_setresuid);
cond_syscall(sys_getresuid);
cond_syscall(sys_setresgid);
cond_syscall(sys_getresgid);
cond_syscall(sys_setgroups);
cond_syscall(sys_getgroups);
cond_syscall(sys_setfsuid);
cond_syscall(sys_setfsgid);
cond_syscall(sys_capget);
cond_syscall(sys_capset);
/* arch-specific weak syscall entries */
cond_syscall(sys_pciconfig_read);
......
config SUNRPC
tristate
depends on MULTIUSER
config SUNRPC_GSS
tristate
select OID_REGISTRY
depends on MULTIUSER
config SUNRPC_BACKCHANNEL
bool
......
......@@ -21,6 +21,7 @@ config SECURITY_DMESG_RESTRICT
config SECURITY
bool "Enable different security models"
depends on SYSFS
depends on MULTIUSER
help
This allows you to choose different security modules to be
configured into your kernel.
......
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