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Date: Thu, 03 Oct 2013 10:12:30 -0700
From: Davidlohr Bueso <davidlohr@...com>
To: Manfred Spraul <manfred@...orfullife.com>
Cc: Davidlohr Bueso <davidlohr.bueso@...com>,
LKML <linux-kernel@...r.kernel.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Mike Galbraith <efault@....de>
Subject: Re: [PATCH v2] ipc/sem.c: synchronize semop and semctl with IPC_RMID
On Thu, 2013-10-03 at 15:26 +0200, Manfred Spraul wrote:
> 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.
>
> Davidlohr: What do you think?
>
Acked-by: Davidlohr Bueso <davidlohr@...com>
> Signed-off-by: Manfred Spraul <manfred@...orfullife.com>
> ---
> ipc/sem.c | 42 +++++++++++++++++++++++++++++-------------
> 1 file changed, 29 insertions(+), 13 deletions(-)
>
> diff --git a/ipc/sem.c b/ipc/sem.c
> index 8c4f59b..db9d241 100644
> --- a/ipc/sem.c
> +++ b/ipc/sem.c
> @@ -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
--
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