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authorIulia Manda <iulia.manda21@gmail.com>2015-04-15 16:16:41 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-04-15 16:35:22 -0700
commit2813893f8b197a14f1e1ddb04d99bce46817c84a (patch)
tree650651e638f867a6bda23e08c70bdd9857d121ca /kernel
parentc79574abe2baddf569532e7e430e4977771dd25c (diff)
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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/Makefile4
-rw-r--r--kernel/capability.c35
-rw-r--r--kernel/cred.c3
-rw-r--r--kernel/groups.c3
-rw-r--r--kernel/sys.c2
-rw-r--r--kernel/sys_ni.c14
6 files changed, 41 insertions, 20 deletions
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
@@ -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 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 <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 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);

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