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ipc/sem.c: synchronize semop and semctl with IPC_RMID 

After acquiring the semlock spinlock, operations must test that the
array is still valid.

 - semctl() and exit_sem() would walk stale linked lists (ugly, but
   should be ok: all lists are empty)

 - semtimedop() would sleep forever - and if woken up due to a signal -
   access memory after free.

The patch also:
 - standardizes the tests for .deleted, so that all tests in one
   function leave the function with the same approach.
 - unconditionally tests for .deleted immediately after every call to
   sem_lock - even it it means that for semctl(GETALL), .deleted will be
   tested twice.

Both changes make the review simpler: After every sem_lock, there must
be a test of .deleted, followed by a goto to the cleanup code (if the
function uses "goto cleanup").

The only exception is semctl_down(): If sem_ids().rwsem is locked, then
the presence in ids->ipcs_idr is equivalent to !.deleted, thus no
additional test is required.

Signed-off-by: Manfred Spraul <manfred@colorfullife.com>
Cc: Mike Galbraith <efault@gmx.de>
Acked-by: Davidlohr Bueso <davidlohr@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Manfred Spraul 2013-10-16 13:46:45 -07:00 committed by Linus Torvalds
parent 18ccee263c
commit 6e224f9459
1 changed files with 29 additions and 13 deletions
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42
ipc/sem.c
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@ -1282,6 +1282,12 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
sem_unlock(sma, -1);
rcu_read_unlock();
return -EIDRM;
}
curr = &sma->sem_base[semnum];
ipc_assert_locked_object(&sma->sem_perm);
@ -1336,12 +1342,14 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int i;
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
err = -EIDRM;
goto out_unlock;
}
if(nsems > SEMMSL_FAST) {
if (!ipc_rcu_getref(sma)) {
sem_unlock(sma, -1);
rcu_read_unlock();
err = -EIDRM;
goto out_free;
goto out_unlock;
}
sem_unlock(sma, -1);
rcu_read_unlock();
@ -1354,10 +1362,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
sem_unlock(sma, -1);
rcu_read_unlock();
err = -EIDRM;
goto out_free;
goto out_unlock;
}
}
for (i = 0; i < sma->sem_nsems; i++)
@ -1375,8 +1381,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
struct sem_undo *un;
if (!ipc_rcu_getref(sma)) {
rcu_read_unlock();
return -EIDRM;
err = -EIDRM;
goto out_rcu_wakeup;
}
rcu_read_unlock();
@ -1404,10 +1410,8 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
rcu_read_lock();
sem_lock_and_putref(sma);
if (sma->sem_perm.deleted) {
sem_unlock(sma, -1);
rcu_read_unlock();
err = -EIDRM;
goto out_free;
goto out_unlock;
}
for (i = 0; i < nsems; i++)
@ -1431,6 +1435,10 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
goto out_rcu_wakeup;
sem_lock(sma, NULL, -1);
if (sma->sem_perm.deleted) {
err = -EIDRM;
goto out_unlock;
}
curr = &sma->sem_base[semnum];
switch (cmd) {
@ -1836,6 +1844,10 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
if (error)
goto out_rcu_wakeup;
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
if (sma->sem_perm.deleted)
goto out_unlock_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
* allocated an undo structure, it was invalidated by an RMID
@ -1843,8 +1855,6 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
* This case can be detected checking un->semid. The existence of
* "un" itself is guaranteed by rcu.
*/
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
if (un && un->semid == -1)
goto out_unlock_free;
@ -2057,6 +2067,12 @@ void exit_sem(struct task_struct *tsk)
}
sem_lock(sma, NULL, -1);
/* exit_sem raced with IPC_RMID, nothing to do */
if (sma->sem_perm.deleted) {
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
}
un = __lookup_undo(ulp, semid);
if (un == NULL) {
/* exit_sem raced with IPC_RMID+semget() that created