From 53dad6d3a8e5ac1af8bacc6ac2134ae1a8b085f1 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Mon, 23 Sep 2013 17:04:45 -0700 Subject: ipc: fix race with LSMs Currently, IPC mechanisms do security and auditing related checks under RCU. However, since security modules can free the security structure, for example, through selinux_[sem,msg_queue,shm]_free_security(), we can race if the structure is freed before other tasks are done with it, creating a use-after-free condition. Manfred illustrates this nicely, for instance with shared mem and selinux: -> do_shmat calls rcu_read_lock() -> do_shmat calls shm_object_check(). Checks that the object is still valid - but doesn't acquire any locks. Then it returns. -> do_shmat calls security_shm_shmat (e.g. selinux_shm_shmat) -> selinux_shm_shmat calls ipc_has_perm() -> ipc_has_perm accesses ipc_perms->security shm_close() -> shm_close acquires rw_mutex & shm_lock -> shm_close calls shm_destroy -> shm_destroy calls security_shm_free (e.g. selinux_shm_free_security) -> selinux_shm_free_security calls ipc_free_security(&shp->shm_perm) -> ipc_free_security calls kfree(ipc_perms->security) This patch delays the freeing of the security structures after all RCU readers are done. Furthermore it aligns the security life cycle with that of the rest of IPC - freeing them based on the reference counter. For situations where we need not free security, the current behavior is kept. Linus states: "... the old behavior was suspect for another reason too: having the security blob go away from under a user sounds like it could cause various other problems anyway, so I think the old code was at least _prone_ to bugs even if it didn't have catastrophic behavior." I have tested this patch with IPC testcases from LTP on both my quad-core laptop and on a 64 core NUMA server. In both cases selinux is enabled, and tests pass for both voluntary and forced preemption models. While the mentioned races are theoretical (at least no one as reported them), I wanted to make sure that this new logic doesn't break anything we weren't aware of. Suggested-by: Linus Torvalds Signed-off-by: Davidlohr Bueso Acked-by: Manfred Spraul Signed-off-by: Linus Torvalds --- ipc/msg.c | 19 +++++++++++++------ 1 file changed, 13 insertions(+), 6 deletions(-) (limited to 'ipc/msg.c') diff --git a/ipc/msg.c b/ipc/msg.c index b0d541d42677..9e4310c546ae 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -165,6 +165,15 @@ static inline void msg_rmid(struct ipc_namespace *ns, struct msg_queue *s) ipc_rmid(&msg_ids(ns), &s->q_perm); } +static void msg_rcu_free(struct rcu_head *head) +{ + struct ipc_rcu *p = container_of(head, struct ipc_rcu, rcu); + struct msg_queue *msq = ipc_rcu_to_struct(p); + + security_msg_queue_free(msq); + ipc_rcu_free(head); +} + /** * newque - Create a new msg queue * @ns: namespace @@ -189,15 +198,14 @@ static int newque(struct ipc_namespace *ns, struct ipc_params *params) msq->q_perm.security = NULL; retval = security_msg_queue_alloc(msq); if (retval) { - ipc_rcu_putref(msq); + ipc_rcu_putref(msq, ipc_rcu_free); return retval; } /* ipc_addid() locks msq upon success. */ id = ipc_addid(&msg_ids(ns), &msq->q_perm, ns->msg_ctlmni); if (id < 0) { - security_msg_queue_free(msq); - ipc_rcu_putref(msq); + ipc_rcu_putref(msq, msg_rcu_free); return id; } @@ -276,8 +284,7 @@ static void freeque(struct ipc_namespace *ns, struct kern_ipc_perm *ipcp) free_msg(msg); } atomic_sub(msq->q_cbytes, &ns->msg_bytes); - security_msg_queue_free(msq); - ipc_rcu_putref(msq); + ipc_rcu_putref(msq, msg_rcu_free); } /* @@ -717,7 +724,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, rcu_read_lock(); ipc_lock_object(&msq->q_perm); - ipc_rcu_putref(msq); + ipc_rcu_putref(msq, ipc_rcu_free); if (msq->q_perm.deleted) { err = -EIDRM; goto out_unlock0; -- cgit v1.2.3 From 4271b05a227dc6175b66c3d9941aeab09048aeb2 Mon Sep 17 00:00:00 2001 From: Davidlohr Bueso Date: Mon, 30 Sep 2013 13:45:26 -0700 Subject: ipc,msg: prevent race with rmid in msgsnd,msgrcv This fixes a race in both msgrcv() and msgsnd() between finding the msg and actually dealing with the queue, as another thread can delete shmid underneath us if we are preempted before acquiring the kern_ipc_perm.lock. Manfred illustrates this nicely: Assume a preemptible kernel that is preempted just after msq = msq_obtain_object_check(ns, msqid) in do_msgrcv(). The only lock that is held is rcu_read_lock(). Now the other thread processes IPC_RMID. When the first task is resumed, then it will happily wait for messages on a deleted queue. Fix this by checking for if the queue has been deleted after taking the lock. Signed-off-by: Davidlohr Bueso Reported-by: Manfred Spraul Cc: Rik van Riel Cc: Mike Galbraith Cc: [3.11] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/msg.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'ipc/msg.c') diff --git a/ipc/msg.c b/ipc/msg.c index 9e4310c546ae..558aa91186b6 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -695,6 +695,12 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, if (ipcperms(ns, &msq->q_perm, S_IWUGO)) goto out_unlock0; + /* raced with RMID? */ + if (msq->q_perm.deleted) { + err = -EIDRM; + goto out_unlock0; + } + err = security_msg_queue_msgsnd(msq, msg, msgflg); if (err) goto out_unlock0; @@ -901,6 +907,13 @@ long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgfl goto out_unlock1; ipc_lock_object(&msq->q_perm); + + /* raced with RMID? */ + if (msq->q_perm.deleted) { + msg = ERR_PTR(-EIDRM); + goto out_unlock0; + } + msg = find_msg(msq, &msgtyp, mode); if (!IS_ERR(msg)) { /* -- cgit v1.2.3