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authorRafael Aquini <aquini@redhat.com>2014-01-27 17:07:01 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-01-27 21:02:39 -0800
commit0f3d2b0135f4bdbfe47a99753923a64efd373d11 (patch)
tree4b211b7502e2412aedd94400bdcb012a2b5814b3 /ipc
parent78f5009cc35eb5e52d276a046d90ee2f41b60f8c (diff)
downloadlinux-0f3d2b0135f4bdbfe47a99753923a64efd373d11.tar.gz
ipc: introduce ipc_valid_object() helper to sort out IPC_RMID races
After the locking semantics for the SysV IPC API got improved, a couple of IPC_RMID race windows were opened because we ended up dropping the 'kern_ipc_perm.deleted' check performed way down in ipc_lock(). The spotted races got sorted out by re-introducing the old test within the racy critical sections. This patch introduces ipc_valid_object() to consolidate the way we cope with IPC_RMID races by using the same abstraction across the API implementation. Signed-off-by: Rafael Aquini <aquini@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Acked-by: Greg Thelen <gthelen@google.com> Reviewed-by: Davidlohr Bueso <davidlohr@hp.com> Cc: Manfred Spraul <manfred@colorfullife.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'ipc')
-rw-r--r--ipc/msg.c7
-rw-r--r--ipc/sem.c24
-rw-r--r--ipc/shm.c16
-rw-r--r--ipc/util.h13
4 files changed, 41 insertions, 19 deletions
diff --git a/ipc/msg.c b/ipc/msg.c
index 558aa91186b..8983ea57d97 100644
--- a/ipc/msg.c
+++ b/ipc/msg.c
@@ -696,7 +696,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
goto out_unlock0;
/* raced with RMID? */
- if (msq->q_perm.deleted) {
+ if (!ipc_valid_object(&msq->q_perm)) {
err = -EIDRM;
goto out_unlock0;
}
@@ -731,7 +731,8 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext,
ipc_lock_object(&msq->q_perm);
ipc_rcu_putref(msq, ipc_rcu_free);
- if (msq->q_perm.deleted) {
+ /* raced with RMID? */
+ if (!ipc_valid_object(&msq->q_perm)) {
err = -EIDRM;
goto out_unlock0;
}
@@ -909,7 +910,7 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl
ipc_lock_object(&msq->q_perm);
/* raced with RMID? */
- if (msq->q_perm.deleted) {
+ if (!ipc_valid_object(&msq->q_perm)) {
msg = ERR_PTR(-EIDRM);
goto out_unlock0;
}
diff --git a/ipc/sem.c b/ipc/sem.c
index cc9ac35b793..4d88194a5ff 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -1284,7 +1284,7 @@ static int semctl_setval(struct ipc_namespace *ns, int semid, int semnum,
sem_lock(sma, NULL, -1);
- if (sma->sem_perm.deleted) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
return -EIDRM;
@@ -1344,7 +1344,7 @@ static int semctl_main(struct ipc_namespace *ns, int semid, int semnum,
int i;
sem_lock(sma, NULL, -1);
- if (sma->sem_perm.deleted) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@@ -1363,7 +1363,7 @@ 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) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@@ -1411,7 +1411,7 @@ 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) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@@ -1437,7 +1437,7 @@ 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) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
err = -EIDRM;
goto out_unlock;
}
@@ -1701,7 +1701,7 @@ static struct sem_undo *find_alloc_undo(struct ipc_namespace *ns, int semid)
/* step 3: Acquire the lock on semaphore array */
rcu_read_lock();
sem_lock_and_putref(sma);
- if (sma->sem_perm.deleted) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
kfree(new);
@@ -1848,7 +1848,15 @@ SYSCALL_DEFINE4(semtimedop, int, semid, struct sembuf __user *, tsops,
error = -EIDRM;
locknum = sem_lock(sma, sops, nsops);
- if (sma->sem_perm.deleted)
+ /*
+ * We eventually might perform the following check in a lockless
+ * fashion, considering ipc_valid_object() locking constraints.
+ * If nsops == 1 and there is no contention for sem_perm.lock, then
+ * only a per-semaphore lock is held and it's OK to proceed with the
+ * check below. More details on the fine grained locking scheme
+ * entangled here and why it's RMID race safe on comments at sem_lock()
+ */
+ if (!ipc_valid_object(&sma->sem_perm))
goto out_unlock_free;
/*
* semid identifiers are not unique - find_alloc_undo may have
@@ -2070,7 +2078,7 @@ 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) {
+ if (!ipc_valid_object(&sma->sem_perm)) {
sem_unlock(sma, -1);
rcu_read_unlock();
continue;
diff --git a/ipc/shm.c b/ipc/shm.c
index 7a51443a51d..1bc68f11584 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -975,6 +975,13 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
goto out_unlock1;
ipc_lock_object(&shp->shm_perm);
+
+ /* check if shm_destroy() is tearing down shp */
+ if (!ipc_valid_object(&shp->shm_perm)) {
+ err = -EIDRM;
+ goto out_unlock0;
+ }
+
if (!ns_capable(ns->user_ns, CAP_IPC_LOCK)) {
kuid_t euid = current_euid();
if (!uid_eq(euid, shp->shm_perm.uid) &&
@@ -989,13 +996,6 @@ SYSCALL_DEFINE3(shmctl, int, shmid, int, cmd, struct shmid_ds __user *, buf)
}
shm_file = shp->shm_file;
-
- /* check if shm_destroy() is tearing down shp */
- if (shm_file == NULL) {
- err = -EIDRM;
- goto out_unlock0;
- }
-
if (is_file_hugepages(shm_file))
goto out_unlock0;
@@ -1116,7 +1116,7 @@ long do_shmat(int shmid, char __user *shmaddr, int shmflg, ulong *raddr,
ipc_lock_object(&shp->shm_perm);
/* check if shm_destroy() is tearing down shp */
- if (shp->shm_file == NULL) {
+ if (!ipc_valid_object(&shp->shm_perm)) {
ipc_unlock_object(&shp->shm_perm);
err = -EIDRM;
goto out_unlock;
diff --git a/ipc/util.h b/ipc/util.h
index 59d78aa9498..d05b7085a88 100644
--- a/ipc/util.h
+++ b/ipc/util.h
@@ -185,6 +185,19 @@ static inline void ipc_unlock(struct kern_ipc_perm *perm)
rcu_read_unlock();
}
+/*
+ * ipc_valid_object() - helper to sort out IPC_RMID races for codepaths
+ * where the respective ipc_ids.rwsem is not being held down.
+ * Checks whether the ipc object is still around or if it's gone already, as
+ * ipc_rmid() may have already freed the ID while the ipc lock was spinning.
+ * Needs to be called with kern_ipc_perm.lock held -- exception made for one
+ * checkpoint case at sys_semtimedop() as noted in code commentary.
+ */
+static inline bool ipc_valid_object(struct kern_ipc_perm *perm)
+{
+ return perm->deleted == 0;
+}
+
struct kern_ipc_perm *ipc_obtain_object_check(struct ipc_ids *ids, int id);
int ipcget(struct ipc_namespace *ns, struct ipc_ids *ids,
struct ipc_ops *ops, struct ipc_params *params);