Commit ee18d64c authored by David Howells's avatar David Howells Committed by James Morris
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KEYS: Add a keyctl to install a process's session keyring on its parent [try #6]



Add a keyctl to install a process's session keyring onto its parent.  This
replaces the parent's session keyring.  Because the COW credential code does
not permit one process to change another process's credentials directly, the
change is deferred until userspace next starts executing again.  Normally this
will be after a wait*() syscall.

To support this, three new security hooks have been provided:
cred_alloc_blank() to allocate unset security creds, cred_transfer() to fill in
the blank security creds and key_session_to_parent() - which asks the LSM if
the process may replace its parent's session keyring.

The replacement may only happen if the process has the same ownership details
as its parent, and the process has LINK permission on the session keyring, and
the session keyring is owned by the process, and the LSM permits it.

Note that this requires alteration to each architecture's notify_resume path.
This has been done for all arches barring blackfin, m68k* and xtensa, all of
which need assembly alteration to support TIF_NOTIFY_RESUME.  This allows the
replacement to be performed at the point the parent process resumes userspace
execution.

This allows the userspace AFS pioctl emulation to fully emulate newpag() and
the VIOCSETTOK and VIOCSETTOK2 pioctls, all of which require the ability to
alter the parent process's PAG membership.  However, since kAFS doesn't use
PAGs per se, but rather dumps the keys into the session keyring, the session
keyring of the parent must be replaced if, for example, VIOCSETTOK is passed
the newpag flag.

This can be tested with the following program:

	#include <stdio.h>
	#include <stdlib.h>
	#include <keyutils.h>

	#define KEYCTL_SESSION_TO_PARENT	18

	#define OSERROR(X, S) do { if ((long)(X) == -1) { perror(S); exit(1); } } while(0)

	int main(int argc, char **argv)
	{
		key_serial_t keyring, key;
		long ret;

		keyring = keyctl_join_session_keyring(argv[1]);
		OSERROR(keyring, "keyctl_join_session_keyring");

		key = add_key("user", "a", "b", 1, keyring);
		OSERROR(key, "add_key");

		ret = keyctl(KEYCTL_SESSION_TO_PARENT);
		OSERROR(ret, "KEYCTL_SESSION_TO_PARENT");

		return 0;
	}

Compiled and linked with -lkeyutils, you should see something like:

	[dhowells@andromeda ~]$ keyctl show
	Session Keyring
	       -3 --alswrv   4043  4043  keyring: _ses
	355907932 --alswrv   4043    -1   \_ keyring: _uid.4043
	[dhowells@andromeda ~]$ /tmp/newpag
	[dhowells@andromeda ~]$ keyctl show
	Session Keyring
	       -3 --alswrv   4043  4043  keyring: _ses
	1055658746 --alswrv   4043  4043   \_ user: a
	[dhowells@andromeda ~]$ /tmp/newpag hello
	[dhowells@andromeda ~]$ keyctl show
	Session Keyring
	       -3 --alswrv   4043  4043  keyring: hello
	340417692 --alswrv   4043  4043   \_ user: a

Where the test program creates a new session keyring, sticks a user key named
'a' into it and then installs it on its parent.
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent d0420c83
......@@ -757,6 +757,26 @@ The keyctl syscall functions are:
successful.
(*) Install the calling process's session keyring on its parent.
long keyctl(KEYCTL_SESSION_TO_PARENT);
This functions attempts to install the calling process's session keyring
on to the calling process's parent, replacing the parent's current session
keyring.
The calling process must have the same ownership as its parent, the
keyring must have the same ownership as the calling process, the calling
process must have LINK permission on the keyring and the active LSM module
mustn't deny permission, otherwise error EPERM will be returned.
Error ENOMEM will be returned if there was insufficient memory to complete
the operation, otherwise 0 will be returned to indicate success.
The keyring will be replaced next time the parent process leaves the
kernel and resumes executing userspace.
===============
KERNEL SERVICES
===============
......
......@@ -687,5 +687,7 @@ do_notify_resume(struct pt_regs *regs, struct switch_stack *sw,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -711,5 +711,7 @@ do_notify_resume(struct pt_regs *regs, unsigned int thread_flags, int syscall)
if (thread_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -326,5 +326,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, struct thread_info *ti)
if (ti->flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -40,5 +40,7 @@ void do_notify_resume(int canrestart, struct pt_regs *regs,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -572,6 +572,8 @@ asmlinkage void do_notify_resume(__u32 thread_info_flags)
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(__frame);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
} /* end do_notify_resume() */
......@@ -556,5 +556,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, u32 thread_info_flags)
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -192,6 +192,8 @@ do_notify_resume_user(sigset_t *unused, struct sigscratch *scr, long in_syscall)
if (test_thread_flag(TIF_NOTIFY_RESUME)) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(&scr->pt);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
/* copy user rbs to kernel rbs */
......
......@@ -411,6 +411,8 @@ void do_notify_resume(struct pt_regs *regs, sigset_t *oldset,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
clear_thread_flag(TIF_IRET);
......
......@@ -704,5 +704,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, void *unused,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -568,5 +568,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, u32 thread_info_flags)
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(__frame);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -649,5 +649,7 @@ void do_notify_resume(struct pt_regs *regs, long in_syscall)
if (test_thread_flag(TIF_NOTIFY_RESUME)) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -536,4 +536,6 @@ void do_notify_resume(struct pt_regs *regs)
{
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
......@@ -640,5 +640,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, unsigned int save_r0,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -772,5 +772,7 @@ asmlinkage void do_notify_resume(struct pt_regs *regs, unsigned long thread_info
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -590,6 +590,8 @@ void do_notify_resume(struct pt_regs *regs, unsigned long orig_i0,
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......
......@@ -613,5 +613,8 @@ void do_notify_resume(struct pt_regs *regs, unsigned long orig_i0, unsigned long
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
}
......@@ -869,6 +869,8 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
if (thread_info_flags & _TIF_NOTIFY_RESUME) {
clear_thread_flag(TIF_NOTIFY_RESUME);
tracehook_notify_resume(regs);
if (current->replacement_session_keyring)
key_replace_session_keyring();
}
#ifdef CONFIG_X86_32
......
......@@ -152,6 +152,7 @@ struct cred {
extern void __put_cred(struct cred *);
extern void exit_creds(struct task_struct *);
extern int copy_creds(struct task_struct *, unsigned long);
extern struct cred *cred_alloc_blank(void);
extern struct cred *prepare_creds(void);
extern struct cred *prepare_exec_creds(void);
extern struct cred *prepare_usermodehelper_creds(void);
......
......@@ -278,6 +278,8 @@ static inline key_serial_t key_serial(struct key *key)
extern ctl_table key_sysctls[];
#endif
extern void key_replace_session_keyring(void);
/*
* the userspace interface
*/
......@@ -300,6 +302,7 @@ extern void key_init(void);
#define key_fsuid_changed(t) do { } while(0)
#define key_fsgid_changed(t) do { } while(0)
#define key_init() do { } while(0)
#define key_replace_session_keyring() do { } while(0)
#endif /* CONFIG_KEYS */
#endif /* __KERNEL__ */
......
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