On Thu, 30 Nov 2017, Philippe Mikoyan wrote:
As described in the title, this patch fixes <ipc>id_ds inconsistency
when <ipc>ctl_stat runs concurrently with some ds-changing function,
e.g. shmat, msgsnd or whatever.
For instance, if shmctl(IPC_STAT) is running concurrently with shmat,
following data structure can be returned:
{... shm_lpid = 0, shm_nattch = 1, ...}
Hmm yeah that's pretty fishy, also shm_atime = 0, no?
So I think this patch is fine as we can obviously race at a user level.
This is another justification for converting the ipc lock to rwlock;
performance wise they are the pretty much the same (being queued)...
but that's irrelevant to this patch. I like that you manage to do
security and such checks still only under rcu, like all ipc calls
work; *_stat() is no longer special.
With a nit below:
Reviewed-by: Davidlohr Bueso <dbu...@suse.de>
diff --git a/ipc/util.c b/ipc/util.c
index 78755873cc5b..8d3c3946c825 100644
--- a/ipc/util.c
+++ b/ipc/util.c
@@ -22,9 +22,12 @@
* tree.
* - perform initial checks (capabilities, auditing and permission,
* etc).
- * - perform read-only operations, such as STAT, INFO commands.
+ * - perform read-only operations, such as INFO command, that
+ * do not demand atomicity
* acquire the ipc lock (kern_ipc_perm.lock) through
* ipc_lock_object()
+ * - perform read-only operatoins that demand atomicity,
^^ typo
+ * such as STAT command.
* - perform data updates, such as SET, RMID commands and
* mechanism-specific operations (semop/semtimedop,
* msgsnd/msgrcv, shmat/shmdt).
Thanks,
Davidlohr
