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 <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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/capability.h b/include/linux/capability.h
index aa93e5e..af9f0b9 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -205,6 +205,7 @@
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 @@
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);