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authorOleg Nesterov <oleg@redhat.com>2012-05-11 10:59:08 +1000
committerAl Viro <viro@zeniv.linux.org.uk>2012-05-23 22:11:23 -0400
commit413cd3d9abeaef590e5ce00564f7a443165db238 (patch)
treefc7d254053793a95d1470f7c9eafb782d8cf91d6 /security
parent4d1d61a6b203d957777d73fcebf19d90b038b5b2 (diff)
downloadlinux-413cd3d9abeaef590e5ce00564f7a443165db238.tar.gz
keys: change keyctl_session_to_parent() to use task_work_add()
Change keyctl_session_to_parent() to use task_work_add() and move key_replace_session_keyring() logic into task_work->func(). Note that we do task_work_cancel() before task_work_add() to ensure that only one work can be pending at any time. This is important, we must not allow user-space to abuse the parent's ->task_works list. The callback, replace_session_keyring(), checks PF_EXITING. I guess this is not really needed but looks better. As a side effect, this fixes the (unlikely) race. The callers of key_replace_session_keyring() and keyctl_session_to_parent() lack the necessary barriers, the parent can miss the request. Now we can remove task_struct->replacement_session_keyring and related code. Signed-off-by: Oleg Nesterov <oleg@redhat.com> Acked-by: David Howells <dhowells@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Richard Kuo <rkuo@codeaurora.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Alexander Gordeev <agordeev@redhat.com> Cc: Chris Zankel <chris@zankel.net> Cc: David Smith <dsmith@redhat.com> Cc: "Frank Ch. Eigler" <fche@redhat.com> Cc: Geert Uytterhoeven <geert@linux-m68k.org> Cc: Larry Woodman <lwoodman@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Tejun Heo <tj@kernel.org> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'security')
-rw-r--r--security/keys/internal.h2
-rw-r--r--security/keys/keyctl.c63
-rw-r--r--security/keys/process_keys.c20
3 files changed, 44 insertions, 41 deletions
diff --git a/security/keys/internal.h b/security/keys/internal.h
index f711b094ed4..3dcbf86b0d3 100644
--- a/security/keys/internal.h
+++ b/security/keys/internal.h
@@ -14,6 +14,7 @@
#include <linux/sched.h>
#include <linux/key-type.h>
+#include <linux/task_work.h>
#ifdef __KDEBUG
#define kenter(FMT, ...) \
@@ -148,6 +149,7 @@ extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
#define KEY_LOOKUP_FOR_UNLINK 0x04
extern long join_session_keyring(const char *name);
+extern void key_change_session_keyring(struct task_work *twork);
extern struct work_struct key_gc_work;
extern unsigned key_gc_delay;
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index 534a634283a..2f28126215a 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1456,47 +1456,55 @@ long keyctl_session_to_parent(void)
{
struct task_struct *me, *parent;
const struct cred *mycred, *pcred;
- struct cred *cred, *oldcred;
+ struct task_work *newwork, *oldwork;
key_ref_t keyring_r;
+ struct cred *cred;
int ret;
keyring_r = lookup_user_key(KEY_SPEC_SESSION_KEYRING, 0, KEY_LINK);
if (IS_ERR(keyring_r))
return PTR_ERR(keyring_r);
+ ret = -ENOMEM;
+ newwork = kmalloc(sizeof(struct task_work), GFP_KERNEL);
+ if (!newwork)
+ goto error_keyring;
+
/* our parent is going to need a new cred struct, a new tgcred struct
* and new security data, so we allocate them here to prevent ENOMEM in
* our parent */
- ret = -ENOMEM;
cred = cred_alloc_blank();
if (!cred)
- goto error_keyring;
+ goto error_newwork;
cred->tgcred->session_keyring = key_ref_to_ptr(keyring_r);
- keyring_r = NULL;
+ init_task_work(newwork, key_change_session_keyring, cred);
me = current;
rcu_read_lock();
write_lock_irq(&tasklist_lock);
- parent = me->real_parent;
ret = -EPERM;
+ oldwork = NULL;
+ parent = me->real_parent;
/* the parent mustn't be init and mustn't be a kernel thread */
if (parent->pid <= 1 || !parent->mm)
- goto not_permitted;
+ goto unlock;
/* the parent must be single threaded */
if (!thread_group_empty(parent))
- goto not_permitted;
+ goto unlock;
/* the parent and the child must have different session keyrings or
* there's no point */
mycred = current_cred();
pcred = __task_cred(parent);
if (mycred == pcred ||
- mycred->tgcred->session_keyring == pcred->tgcred->session_keyring)
- goto already_same;
+ mycred->tgcred->session_keyring == pcred->tgcred->session_keyring) {
+ ret = 0;
+ goto unlock;
+ }
/* the parent must have the same effective ownership and mustn't be
* SUID/SGID */
@@ -1506,38 +1514,37 @@ long keyctl_session_to_parent(void)
pcred->gid != mycred->egid ||
pcred->egid != mycred->egid ||
pcred->sgid != mycred->egid)
- goto not_permitted;
+ goto unlock;
/* the keyrings must have the same UID */
if ((pcred->tgcred->session_keyring &&
pcred->tgcred->session_keyring->uid != mycred->euid) ||
mycred->tgcred->session_keyring->uid != mycred->euid)
- goto not_permitted;
+ goto unlock;
- /* if there's an already pending keyring replacement, then we replace
- * that */
- oldcred = parent->replacement_session_keyring;
+ /* cancel an already pending keyring replacement */
+ oldwork = task_work_cancel(parent, key_change_session_keyring);
/* the replacement session keyring is applied just prior to userspace
* restarting */
- parent->replacement_session_keyring = cred;
- cred = NULL;
- set_ti_thread_flag(task_thread_info(parent), TIF_NOTIFY_RESUME);
-
- write_unlock_irq(&tasklist_lock);
- rcu_read_unlock();
- if (oldcred)
- put_cred(oldcred);
- return 0;
-
-already_same:
- ret = 0;
-not_permitted:
+ ret = task_work_add(parent, newwork, true);
+ if (!ret)
+ newwork = NULL;
+unlock:
write_unlock_irq(&tasklist_lock);
rcu_read_unlock();
- put_cred(cred);
+ if (oldwork) {
+ put_cred(oldwork->data);
+ kfree(oldwork);
+ }
+ if (newwork) {
+ put_cred(newwork->data);
+ kfree(newwork);
+ }
return ret;
+error_newwork:
+ kfree(newwork);
error_keyring:
key_ref_put(keyring_r);
return ret;
diff --git a/security/keys/process_keys.c b/security/keys/process_keys.c
index d71056db7b6..4ad54eea1ea 100644
--- a/security/keys/process_keys.c
+++ b/security/keys/process_keys.c
@@ -834,23 +834,17 @@ error:
* Replace a process's session keyring on behalf of one of its children when
* the target process is about to resume userspace execution.
*/
-void key_replace_session_keyring(void)
+void key_change_session_keyring(struct task_work *twork)
{
- const struct cred *old;
- struct cred *new;
-
- if (!current->replacement_session_keyring)
- return;
+ const struct cred *old = current_cred();
+ struct cred *new = twork->data;
- write_lock_irq(&tasklist_lock);
- new = current->replacement_session_keyring;
- current->replacement_session_keyring = NULL;
- write_unlock_irq(&tasklist_lock);
-
- if (!new)
+ kfree(twork);
+ if (unlikely(current->flags & PF_EXITING)) {
+ put_cred(new);
return;
+ }
- old = current_cred();
new-> uid = old-> uid;
new-> euid = old-> euid;
new-> suid = old-> suid;