From 2813893f8b197a14f1e1ddb04d99bce46817c84a Mon Sep 17 00:00:00 2001 From: Iulia Manda Date: Wed, 15 Apr 2015 16:16:41 -0700 Subject: 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 --- include/linux/uidgid.h | 12 ++++++++++++ 1 file changed, 12 insertions(+) (limited to 'include/linux/uidgid.h') 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) -- cgit