Messages in this thread | | | Date | Wed, 10 Feb 2010 10:30:33 -0600 | From | "Serge E. Hallyn" <> | Subject | Re: [PATCH] Update comment on find_task_by_pid_ns |
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Quoting Andrew Morton (akpm@linux-foundation.org): > On Tue, 9 Feb 2010 06:42:45 +0900 > Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote: > > > OK. I updated description. > > > > As of 2.6.32 , below users are missing rcu_read_lock(). > > > > Users missing rcu_read_lock() when calling find_task_by_vpid(): > > > > SYSCALL_DEFINE3(ioprio_set) in fs/ioprio.c > > SYSCALL_DEFINE2(ioprio_get) in fs/ioprio.c > > cap_get_target_pid() in kernel/capability.c > > Actually, cap_get_target_pid() uses rcu_read_lock() and doesn't take > tasklist_lock.
Hmm - is that in -mm? In my copy here it takes read_lock(&tasklist_lock)
And I'll admit I'm a bit confused as to the current state of things: do I understand correctly that we now need to take both the tasklist_lock and rcu_read_lock? (Presumably only for read_lock()?)
> > audit_prepare_user_tty() in kernel/audit.c > > audit_receive_msg() in kernel/audit.c > > check_clock() in kernel/posix-cpu-timers.c > > posix_cpu_timer_create() in kernel/posix-cpu-timers.c > > SYSCALL_DEFINE3(setpriority) in kernel/sys.c > > SYSCALL_DEFINE2(getpriority) in kernel/sys.c > > SYSCALL_DEFINE2(setpgid) in kernel/sys.c > > SYSCALL_DEFINE1(sched_getscheduler) in kernel/sched.c > > SYSCALL_DEFINE2(sched_getparam) in kernel/sched.c > > sched_setaffinity() in kernel/sched.c > > sched_getaffinity() in kernel/sched.c > > SYSCALL_DEFINE2(sched_rr_get_interval) in kernel/sched.c > > tomoyo_is_select_one() in security/tomoyo/common.c > > tomoyo_read_pid() in security/tomoyo/common.c > > SYSCALL_DEFINE6(move_pages) in mm/migrate.c > > SYSCALL_DEFINE4(migrate_pages) in mm/mempolicy.c > > find_process_by_pid() in arch/mips/kernel/mips-mt-fpaff.c > > pfm_get_task() in arch/ia64/kernel/perfmon.c > > cxn_pin_by_pid() in arch/frv/mm/mmu-context.c > > > > Users missing rcu_read_lock() when calling find_task_by_pid_ns(): > > > > rest_init() in init/main.c > > getthread() in kernel/kgdb.c > > mconsole_stack() in arch/um/drivers/mconsole_kern.c > > > > What should we do? Adding rcu_read_lock()/rcu_read_unlock() to each > > callers? Or adding rcu_read_lock()/rcu_read_unlock() inside > > find_task_by_pid_ns()? > > Putting rcu_read_lock() in the callee isn't a complete solution. > Because the function would still be returning a task_struct* without > any locking held and without taking a reference against it. So that > pointer is useless to the caller! > > We could add a new function which looks up the task and then takes a > reference on it, insde suitable locks. The caller would then use the > task_struct and then remember to call put_task_struct() to unpin it. > This prevents the task_struct from getting freed while it's being > manipulated, but it doesn't prevent fields within it from being altered > - that's up to the caller to sort out. > > One fix is to go through all those callsites and add the rcu_read_lock. > That kinda sucks. Perhaps writing the new function which returns a > pinned task_struct is better? > > -- > To unsubscribe from this list: send the line "unsubscribe linux-security-module" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
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