From 368ae537e056acd3f751fa276f48423f06803922 Mon Sep 17 00:00:00 2001 From: Svenning Sørensen Date: Wed, 28 Aug 2013 16:35:17 -0700 Subject: IPC: bugfix for msgrcv with msgtyp < 0 According to 'man msgrcv': "If msgtyp is less than 0, the first message of the lowest type that is less than or equal to the absolute value of msgtyp shall be received." Bug: The kernel only returns a message if its type is 1; other messages with type < abs(msgtype) will never get returned. Fix: After having traversed the list to find the first message with the lowest type, we need to actually return that message. This regression was introduced by commit daaf74cf0867 ("ipc: refactor msg list search into separate function") Signed-off-by: Svenning Soerensen Reviewed-by: Peter Hurley Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- ipc/msg.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) (limited to 'ipc/msg.c') diff --git a/ipc/msg.c b/ipc/msg.c index bd60d7e159e..9f29d9e89ba 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -839,7 +839,7 @@ static inline void free_copy(struct msg_msg *copy) static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode) { - struct msg_msg *msg; + struct msg_msg *msg, *found = NULL; long count = 0; list_for_each_entry(msg, &msq->q_messages, m_list) { @@ -848,6 +848,7 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode) *msgtyp, mode)) { if (mode == SEARCH_LESSEQUAL && msg->m_type != 1) { *msgtyp = msg->m_type - 1; + found = msg; } else if (mode == SEARCH_NUMBER) { if (*msgtyp == count) return msg; @@ -857,7 +858,7 @@ static struct msg_msg *find_msg(struct msg_queue *msq, long *msgtyp, int mode) } } - return ERR_PTR(-EAGAIN); + return found ?: ERR_PTR(-EAGAIN); } long do_msgrcv(int msqid, void __user *buf, size_t bufsz, long msgtyp, int msgflg, -- cgit v1.2.3-70-g09d2 From bebcb928c820d0ee83aca4b192adc195e43e66a2 Mon Sep 17 00:00:00 2001 From: Manfred Spraul Date: Tue, 3 Sep 2013 16:00:08 +0200 Subject: ipc/msg.c: Fix lost wakeup in msgsnd(). The check if the queue is full and adding current to the wait queue of pending msgsnd() operations (ss_add()) must be atomic. Otherwise: - the thread that performs msgsnd() finds a full queue and decides to sleep. - the thread that performs msgrcv() first reads all messages from the queue and then sleeps, because the queue is empty. - the msgrcv() calls do not perform any wakeups, because the msgsnd() task has not yet called ss_add(). - then the msgsnd()-thread first calls ss_add() and then sleeps. Net result: msgsnd() and msgrcv() both sleep forever. Observed with msgctl08 from ltp with a preemptible kernel. Fix: Call ipc_lock_object() before performing the check. The patch also moves security_msg_queue_msgsnd() under ipc_lock_object: - msgctl(IPC_SET) explicitely mentions that it tries to expunge any pending operations that are not allowed anymore with the new permissions. If security_msg_queue_msgsnd() is called without locks, then there might be races. - it makes the patch much simpler. Reported-and-tested-by: Vineet Gupta Acked-by: Rik van Riel Cc: stable@vger.kernel.org # for 3.11 Signed-off-by: Manfred Spraul Signed-off-by: Linus Torvalds --- ipc/msg.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) (limited to 'ipc/msg.c') diff --git a/ipc/msg.c b/ipc/msg.c index 9f29d9e89ba..b65fdf1a09d 100644 --- a/ipc/msg.c +++ b/ipc/msg.c @@ -680,16 +680,18 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, goto out_unlock1; } + ipc_lock_object(&msq->q_perm); + for (;;) { struct msg_sender s; err = -EACCES; if (ipcperms(ns, &msq->q_perm, S_IWUGO)) - goto out_unlock1; + goto out_unlock0; err = security_msg_queue_msgsnd(msq, msg, msgflg); if (err) - goto out_unlock1; + goto out_unlock0; if (msgsz + msq->q_cbytes <= msq->q_qbytes && 1 + msq->q_qnum <= msq->q_qbytes) { @@ -699,10 +701,9 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, /* queue full, wait: */ if (msgflg & IPC_NOWAIT) { err = -EAGAIN; - goto out_unlock1; + goto out_unlock0; } - ipc_lock_object(&msq->q_perm); ss_add(msq, &s); if (!ipc_rcu_getref(msq)) { @@ -730,10 +731,7 @@ long do_msgsnd(int msqid, long mtype, void __user *mtext, goto out_unlock0; } - ipc_unlock_object(&msq->q_perm); } - - ipc_lock_object(&msq->q_perm); msq->q_lspid = task_tgid_vnr(current); msq->q_stime = get_seconds(); -- cgit v1.2.3-70-g09d2