lkml.org 
[lkml]   [2011]   [Jan]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Subject[34-longterm 128/260] pid: make setpgid() system call use RCU read-side critical section
    Date
    From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

    commit 950eaaca681c44aab87a46225c9e44f902c080aa upstream.

    [ 23.584719]
    [ 23.584720] ===================================================
    [ 23.585059] [ INFO: suspicious rcu_dereference_check() usage. ]
    [ 23.585176] ---------------------------------------------------
    [ 23.585176] kernel/pid.c:419 invoked rcu_dereference_check() without protection!
    [ 23.585176]
    [ 23.585176] other info that might help us debug this:
    [ 23.585176]
    [ 23.585176]
    [ 23.585176] rcu_scheduler_active = 1, debug_locks = 1
    [ 23.585176] 1 lock held by rc.sysinit/728:
    [ 23.585176] #0: (tasklist_lock){.+.+..}, at: [<ffffffff8104771f>] sys_setpgid+0x5f/0x193
    [ 23.585176]
    [ 23.585176] stack backtrace:
    [ 23.585176] Pid: 728, comm: rc.sysinit Not tainted 2.6.36-rc2 #2
    [ 23.585176] Call Trace:
    [ 23.585176] [<ffffffff8105b436>] lockdep_rcu_dereference+0x99/0xa2
    [ 23.585176] [<ffffffff8104c324>] find_task_by_pid_ns+0x50/0x6a
    [ 23.585176] [<ffffffff8104c35b>] find_task_by_vpid+0x1d/0x1f
    [ 23.585176] [<ffffffff81047727>] sys_setpgid+0x67/0x193
    [ 23.585176] [<ffffffff810029eb>] system_call_fastpath+0x16/0x1b
    [ 24.959669] type=1400 audit(1282938522.956:4): avc: denied { module_request } for pid=766 comm="hwclock" kmod="char-major-10-135" scontext=system_u:system_r:hwclock_t:s0 tcontext=system_u:system_r:kernel_t:s0 tclas

    It turns out that the setpgid() system call fails to enter an RCU
    read-side critical section before doing a PID-to-task_struct translation.
    This commit therefore does rcu_read_lock() before the translation, and
    also does rcu_read_unlock() after the last use of the returned pointer.

    Reported-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
    Acked-by: David Howells <dhowells@redhat.com>
    Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
    ---
    kernel/sys.c | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/kernel/sys.c b/kernel/sys.c
    index 7cb426a..0324c1c 100644
    --- a/kernel/sys.c
    +++ b/kernel/sys.c
    @@ -962,6 +962,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
    pgid = pid;
    if (pgid < 0)
    return -EINVAL;
    + rcu_read_lock();

    /* From this point forward we keep holding onto the tasklist lock
    * so that our parent does not change from under us. -DaveM
    @@ -1015,6 +1016,7 @@ SYSCALL_DEFINE2(setpgid, pid_t, pid, pid_t, pgid)
    out:
    /* All paths lead to here, thus we are safe. -DaveM */
    write_unlock_irq(&tasklist_lock);
    + rcu_read_unlock();
    return err;
    }

    --
    1.7.3.3


    \
     
     \ /
      Last update: 2011-01-02 08:51    [W:2.356 / U:0.184 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site