On Tue, Sep 3, 2013 at 6:33 PM, Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> wrote: > Hi Sedat, > > > On 09/03/2013 06:13 PM, Sedat Dilek wrote: >> >> On Tue, Sep 3, 2013 at 4:00 PM, Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> >> wrote: >>> >>> 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() calls first reads all messages from >>> the >>> queue and then sleep, because the queue is empty. >> >> reads -> sleeps > > Correct. > >>> - 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. >>> >> I don't know what and why "net result" - net in sense of networking? > > http://en.wiktionary.org/wiki/net#Adjective > I.e.: Ignore/remove the "Net". > > >>> Observed with msgctl08 from ltp with a preemptible kernel. >>> >> ...on ARC arch (that sounds funny somehow). >> >>> 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-by: Vineet Gupta <Vineet.Gupta1@xxxxxxxxxxxx> >>> Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> >> >> I guess this is missing a "CC: stable" as Vineet reported against >> Linux v3.11-rc7 (and should enter v3.11.1)? > > Yes. I didn't notice that Linus already released 3.11. > Linus pushed your patch upstream... with typos fixed and "CC: stable #3.11". Thanks to all involved people! - Sedat - [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=bebcb928c820d0ee83aca4b192adc195e43e66a2 > -- > Manfred > >> - Sedat - >> >>> --- >>> ipc/msg.c | 12 +++++------- >>> 1 file changed, 5 insertions(+), 7 deletions(-) >>> >>> diff --git a/ipc/msg.c b/ipc/msg.c >>> index 9f29d9e..b65fdf1 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(); >>> >>> -- >>> 1.8.3.1 >>> > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>