From 2813893f8b197a14f1e1ddb04d99bce46817c84a Mon Sep 17 00:00:00 2001 From: Iulia Manda Date: Wed, 15 Apr 2015 16:16:41 -0700 Subject: [PATCH] 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: Iulia Manda Reviewed-by: Josh Triplett Acked-by: Geert Uytterhoeven Tested-by: Paul E. McKenney Reviewed-by: Paul E. McKenney Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- 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 a5ced5c3c1e0..de2726a487b0 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -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 diff --git a/drivers/staging/lustre/lustre/Kconfig b/drivers/staging/lustre/lustre/Kconfig index 6725467ef4d0..62c7bba75274 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 c7abc10279af..f31fd0dd92c6 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 683bf718aead..fc2d108f5272 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 aa93e5ef594c..af9f0b9e80e6 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 2fb2ca2127ed..8b6c083e68a7 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 2d1f9b627f91..0ee05da38899 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 a905b7301e10..3b9df1aa35db 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 @@ -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 diff --git a/kernel/Makefile b/kernel/Makefile index 1408b3353a3c..0f8f8b0bc1bf 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 989f5bfc57dc..45432b54d5c6 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 @@ -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 diff --git a/kernel/cred.c b/kernel/cred.c index e0573a43c7df..ec1c07667ec1 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 664411f171b5..74d431d25251 100644 --- a/kernel/groups.c +++ b/kernel/groups.c @@ -9,9 +9,6 @@ #include #include -/* 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 a03d9cd23ed7..3be344902316 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -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 diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c index 5adcb0ae3a58..7995ef5868d8 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 fb78117b896c..9068e72aa73c 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 beb86b500adf..bf4ec46474b6 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.