On Fri, Sep 21, 2007 at 01:03:47PM +0200, Jarek Poplawski wrote: ... > I hope not! But, then it would be probably another logical trick: > ipc_rcu_getref/putref() seems to prevent kfreeing of a structure, so > if it's used in do_msgsnd() there should be a risk something can do > this kfree at this moment, and it seems freeque() is the only one, > which both: can do this and cares for this refcount. Then, e.g., if > any of them does ipc_rcu_getref() a bit later and sees old (cached) > value - kfree can be skipped forever. [...]
After rethinking, this scenario seems to be wrong or very unprobable (I'm not sure of all ways "if (--container...)" could be compiled), so there should be no such risk - double kfree/vfree is more probable, so no danger. More likely is such refcount abuse: ipc_rcu_getref() in do_msgsnd() done a bit after ipc_rcu_putref() in freeque() (msq pointer acquired by do_msgsend() before freeque() started); then, after schedule(), do_msgsnd() can work with kfreed msq_queue structure (at least considering classic RCU). Regards, Jarek P. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/