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SubjectRe: [PATCH v3] kernel: Conditionally support non-root users, groups and capabilities
On Fri, Feb 06, 2015 at 02:03:56AM +0200, Iulia Manda wrote:
> 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.
>
> 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)

I presume that v4 will have your Signed-off-by. ;-)

Testing on my rcutorture setup uncovered an additional required dependency,
please see patch at the end of this email. With that fix, either separately
or merged into your patch:

Tested-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

One question below about moving the definition of capable(). Either way:

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

> ---
> Changes since v2:
> - rename symbol;
> - make SECURITY dependent on MULTIUSER
>
> arch/s390/Kconfig | 1 +
> drivers/staging/lustre/lustre/Kconfig | 1 +
> 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 +
> 15 files changed, 125 insertions(+), 25 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/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);
> -
> -/**

OK, I'll bite... Why are we moving 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

------------------------------------------------------------------------

nfs: Make NFS_FS depend on MULTIUSER

Building with CONFIG_MULTIUSER=n results in the following Kconfig
warnings:

warning: (NFS_FS) selects SUNRPC which has unmet direct dependencies (NETWORK_FILESYSTEMS && MULTIUSER)
warning: (NFS_V4 && NFSD_V4 && RPCSEC_GSS_KRB5) selects SUNRPC_GSS which has unmet direct dependencies (NETWORK_FILESYSTEMS && MULTIUSER)
warning: (NFS_FS) selects SUNRPC which has unmet direct dependencies (NETWORK_FILESYSTEMS && MULTIUSER)
warning: (NFS_V4 && NFSD_V4 && RPCSEC_GSS_KRB5) selects SUNRPC_GSS which has unmet direct dependencies (NETWORK_FILESYSTEMS && MULTIUSER)

This patch makes NFS_FS depend on MULTIUSER, eliminating these warnings.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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


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