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Subject[PATCH v4] 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 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)

Signed-off-by: Iulia Manda <iulia.manda21@gmail.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
arch/s390/Kconfig | 1 +
drivers/staging/lustre/lustre/Kconfig | 1 +
fs/nfs/Kconfig | 2 +-
fs/nfsd/Kconfig | 1 +
include/linux/capability.h | 29 +++++++++++++++++++++++++++
include/linux/cred.h | 23 ++++++++++++++++++----
include/linux/uidgid.h | 12 +++++++++++
init/Kconfig | 19 +++++++++++++++++-
kernel/Makefile | 4 +++-
kernel/capability.c | 35 ++++++++++++++++++---------------
kernel/cred.c | 3 +++
kernel/groups.c | 3 ---
kernel/sys.c | 2 ++
kernel/sys_ni.c | 14 +++++++++++++
net/sunrpc/Kconfig | 2 ++
security/Kconfig | 1 +
16 files changed, 126 insertions(+), 26 deletions(-)

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 68b68d7..71fb2d1 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -324,6 +324,7 @@ 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
diff --git a/drivers/staging/lustre/lustre/Kconfig b/drivers/staging/lustre/lustre/Kconfig
index 6725467..62c7bba 100644
--- a/drivers/staging/lustre/lustre/Kconfig
+++ b/drivers/staging/lustre/lustre/Kconfig
@@ -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
diff --git a/fs/nfs/Kconfig b/fs/nfs/Kconfig
index 3dece03..07a902d 100644
--- a/fs/nfs/Kconfig
+++ b/fs/nfs/Kconfig
@@ -1,6 +1,6 @@
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
diff --git a/fs/nfsd/Kconfig b/fs/nfsd/Kconfig
index 7339515..df0a5d9 100644
--- a/fs/nfsd/Kconfig
+++ b/fs/nfsd/Kconfig
@@ -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
diff --git a/include/linux/capability.h b/include/linux/capability.h
index aa93e5e..0c0ae0d 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -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);

diff --git a/include/linux/cred.h b/include/linux/cred.h
index 2fb2ca2..8b6c083 100644
--- a/include/linux/cred.h
+++ b/include/linux/cred.h
@@ -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
*
diff --git a/include/linux/uidgid.h b/include/linux/uidgid.h
index 2d1f9b6..0ee05da 100644
--- a/include/linux/uidgid.h
+++ b/include/linux/uidgid.h
@@ -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)
diff --git a/init/Kconfig b/init/Kconfig
index 9afb971..b0332c2 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -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
@@ -1140,6 +1142,7 @@ 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
@@ -1352,11 +1355,25 @@ 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
diff --git a/kernel/Makefile b/kernel/Makefile
index a59481a..554d34e 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -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
diff --git a/kernel/capability.c b/kernel/capability.c
index 989f5bf..638b0b3 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -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
@@ -412,22 +431,6 @@ 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
* @cap: The capability in question
diff --git a/kernel/cred.c b/kernel/cred.c
index e0573a4..ec1c076 100644
--- a/kernel/cred.c
+++ b/kernel/cred.c
@@ -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
*/
diff --git a/kernel/groups.c b/kernel/groups.c
index 664411f..74d431d 100644
--- a/kernel/groups.c
+++ b/kernel/groups.c
@@ -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;
diff --git a/kernel/sys.c b/kernel/sys.c
index ea9c881..3094e0f 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -319,6 +319,7 @@ 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();
@@ -809,6 +810,7 @@ change_okay:
commit_creds(new);
return old_fsgid;
}
+#endif /* CONFIG_MULTIUSER */

/**
* sys_getpid - return the thread group id of the current process
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index 5adcb0a..7995ef5 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -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);
diff --git a/net/sunrpc/Kconfig b/net/sunrpc/Kconfig
index fb78117..9068e72 100644
--- a/net/sunrpc/Kconfig
+++ b/net/sunrpc/Kconfig
@@ -1,9 +1,11 @@
config SUNRPC
tristate
+ depends on MULTIUSER

config SUNRPC_GSS
tristate
select OID_REGISTRY
+ depends on MULTIUSER

config SUNRPC_BACKCHANNEL
bool
diff --git a/security/Kconfig b/security/Kconfig
index beb86b5..bf4ec46 100644
--- a/security/Kconfig
+++ b/security/Kconfig
@@ -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.
--
1.7.10.4


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