2014-04-14 07:23:16

by Chen Tingjie

Subject: [PATCH] [PATCH V2] tty: memleak in alloc_pid

There is memleak in alloc_pid:
------------------------------
unreferenced object 0xd3453a80 (size 64):
comm "adbd", pid 1730, jiffies 66363 (age 6586.950s)
hex dump (first 32 bytes):
01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
00 00 00 00 40 c2 f6 d5 00 d3 25 c1 59 28 00 00 ....@.....%.Y(..
backtrace:
[<c1a6f15c>] kmemleak_alloc+0x3c/0xa0
[<c1320546>] kmem_cache_alloc+0xc6/0x190
[<c125d51e>] alloc_pid+0x1e/0x400
[<c123d344>] copy_process.part.39+0xad4/0x1120
[<c123da59>] do_fork+0x99/0x330
[<c123dd58>] sys_fork+0x28/0x30
[<c1a89a08>] syscall_call+0x7/0xb
[<ffffffff>] 0xffffffff

the leak is due to unreleased pid->count, which execute in function:
get_pid()(pid->count++) and put_pid()(pid->count--).

The race condition as following:
task[dumpsys] task[adbd]
in disassociate_ctty() in tty_signal_session_leader()
----------------------- -------------------------
tty = get_current_tty();
// tty is not NULL
...
spin_lock_irq(&current->sighand->siglock);
put_pid(current->signal->tty_old_pgrp);
current->signal->tty_old_pgrp = NULL;
spin_unlock_irq(&current->sighand->siglock);

spin_lock_irq(&p->sighand->siglock);
...
p->signal->tty = NULL;
...
spin_unlock_irq(&p->sighand->siglock);

tty = get_current_tty();
// tty NULL, goto else branch by accident.
if (tty) {
...
put_pid(tty_session);
put_pid(tty_pgrp);
...
} else {
print msg
}

in task[dumpsys], in disassociate_ctty(), tty is set NULL by task[adbd],
tty_signal_session_leader(), then it goto else branch and lack of
put_pid(), cause memleak.

move spin_unlock(sighand->siglock) after get_current_tty() can avoid
the race and fix the memleak.

Change-Id: Ic960dda039c8f99aad3e0f4d176489a966c62f6a
Signed-off-by: Zhang Jun <[email protected]>
Signed-off-by: Chen Tingjie <[email protected]>
---
drivers/tty/tty_io.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 31c4a57..72547a3 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -874,9 +874,8 @@ void disassociate_ctty(int on_exit)
spin_lock_irq(&current->sighand->siglock);
put_pid(current->signal->tty_old_pgrp);
current->signal->tty_old_pgrp = NULL;
- spin_unlock_irq(&current->sighand->siglock);

- tty = get_current_tty();
+ tty = tty_kref_get(current->signal->tty);
if (tty) {
unsigned long flags;
spin_lock_irqsave(&tty->ctrl_lock, flags);
@@ -893,6 +892,7 @@ void disassociate_ctty(int on_exit)
#endif
}

+ spin_unlock_irq(&current->sighand->siglock);
/* Now clear signal->tty under the lock */
read_lock(&tasklist_lock);
session_clear_tty(task_session(current));
--
1.7.9.5

2014-04-14 11:44:11

by Greg KH

Subject: Re: [PATCH] [PATCH V2] tty: memleak in alloc_pid

On Mon, Apr 14, 2014 at 03:31:15PM +0800, Chen Tingjie wrote:
> There is memleak in alloc_pid:
> ------------------------------
> unreferenced object 0xd3453a80 (size 64):
> comm "adbd", pid 1730, jiffies 66363 (age 6586.950s)
> hex dump (first 32 bytes):
> 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> 00 00 00 00 40 c2 f6 d5 00 d3 25 c1 59 28 00 00 ....@.....%.Y(..
> backtrace:
> [<c1a6f15c>] kmemleak_alloc+0x3c/0xa0
> [<c1320546>] kmem_cache_alloc+0xc6/0x190
> [<c125d51e>] alloc_pid+0x1e/0x400
> [<c123d344>] copy_process.part.39+0xad4/0x1120
> [<c123da59>] do_fork+0x99/0x330
> [<c123dd58>] sys_fork+0x28/0x30
> [<c1a89a08>] syscall_call+0x7/0xb
> [<ffffffff>] 0xffffffff
>
> the leak is due to unreleased pid->count, which execute in function:
> get_pid()(pid->count++) and put_pid()(pid->count--).
>
> The race condition as following:
> task[dumpsys] task[adbd]
> in disassociate_ctty() in tty_signal_session_leader()
> ----------------------- -------------------------
> tty = get_current_tty();
> // tty is not NULL
> ...
> spin_lock_irq(&current->sighand->siglock);
> put_pid(current->signal->tty_old_pgrp);
> current->signal->tty_old_pgrp = NULL;
> spin_unlock_irq(&current->sighand->siglock);
>
> spin_lock_irq(&p->sighand->siglock);
> ...
> p->signal->tty = NULL;
> ...
> spin_unlock_irq(&p->sighand->siglock);
>
> tty = get_current_tty();
> // tty NULL, goto else branch by accident.
> if (tty) {
> ...
> put_pid(tty_session);
> put_pid(tty_pgrp);
> ...
> } else {
> print msg
> }
>
> in task[dumpsys], in disassociate_ctty(), tty is set NULL by task[adbd],
> tty_signal_session_leader(), then it goto else branch and lack of
> put_pid(), cause memleak.
>
> move spin_unlock(sighand->siglock) after get_current_tty() can avoid
> the race and fix the memleak.
>
> Change-Id: Ic960dda039c8f99aad3e0f4d176489a966c62f6a

Why is this line here?

2014-04-15 02:49:08

by Chen Tingjie

Subject: RE: [PATCH] [PATCH V2] tty: memleak in alloc_pid

Hello,

The related code in disassociate_ctty() as following:

---------------------------------------
/* sometimes current->signal->tty_old_pgrp is NULL (a stand for tty_old_pgrp not NULL, !a for tty_old_pgrp is NULL) */
spin_lock_irq(&current->sighand->siglock);
put_pid(current->signal->tty_old_pgrp); // when a is NULL, will not actually put_pid() by decrease the count
current->signal->tty_old_pgrp = NULL;
spin_unlock_irq(&current->sighand->siglock);

/* sometimes current->signal->tty is NULL (b stand for signal->tty, !b for signal->tty is NULL) */
tty = get_current_tty();
if (tty) {
unsigned long flags;
spin_lock_irqsave(&tty->ctrl_lock, flags);
put_pid(tty->session);
put_pid(tty->pgrp);
tty->session = NULL;
tty->pgrp = NULL;
spin_unlock_irqrestore(&tty->ctrl_lock, flags);
tty_kref_put(tty);
} else {
#ifdef TTY_DEBUG_HANGUP
printk(KERN_DEBUG "error attempted to write to tty [0x%p]"
" = NULL", tty);
#endif
}
------------------------------------

Commonly there are 2 normal case flow for the code:
1/ in task: getprop: !a --> b

This case, current->signal->tty_old_pgrp is NULL, but get_current_tty() is not NULL,
Really put_pid() as following:
put_pid(tty->session);
put_pid(tty->pgrp);

2/ in task: dumpsys: a --> !b

This case, currnet->signal->tty_old_pgrp is not NULL, but get_current_tty() is NULL,
Really put_pid() as following:
put_pid(current->signal->tty_old_pgrp);

There is one abnormal case:
3/ in task: dumpsys: !a -> !b

This case, because of race, current->signal->tty_old_pgrp and get_current_tty() are NULL,
Lack of put_pid(), pid->count will not be 0 at last, this pid will be leak.


When read the current->signal->tty_old_pgrp and current->signal->tty,
The 2 operations should be atomic, which protected by spinlock: current->sighand->siglock.
So the sentence: spin_unlock_irq(&current->sighand->siglock);
need to move down after tty has process completed.

Thanks,

-----Original Message-----
From: Greg Kroah-Hartman [mailto:[email protected]]
Sent: Monday, April 14, 2014 7:47 PM
To: Chen, Tingjie
Cc: Jiri Slaby; [email protected]; Zhang, Jun
Subject: Re: [PATCH] [PATCH V2] tty: memleak in alloc_pid

On Mon, Apr 14, 2014 at 03:31:15PM +0800, Chen Tingjie wrote:
> There is memleak in alloc_pid:
> ------------------------------
> unreferenced object 0xd3453a80 (size 64):
> comm "adbd", pid 1730, jiffies 66363 (age 6586.950s)
> hex dump (first 32 bytes):
> 01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
> 00 00 00 00 40 c2 f6 d5 00 d3 25 c1 59 28 00 00 ....@.....%.Y(..
> backtrace:
> [<c1a6f15c>] kmemleak_alloc+0x3c/0xa0
> [<c1320546>] kmem_cache_alloc+0xc6/0x190
> [<c125d51e>] alloc_pid+0x1e/0x400
> [<c123d344>] copy_process.part.39+0xad4/0x1120
> [<c123da59>] do_fork+0x99/0x330
> [<c123dd58>] sys_fork+0x28/0x30
> [<c1a89a08>] syscall_call+0x7/0xb
> [<ffffffff>] 0xffffffff
>
> the leak is due to unreleased pid->count, which execute in function:
> get_pid()(pid->count++) and put_pid()(pid->count--).
>
> The race condition as following:
> task[dumpsys] task[adbd]
> in disassociate_ctty() in tty_signal_session_leader()
> ----------------------- -------------------------
> tty = get_current_tty();
> // tty is not NULL
> ...
> spin_lock_irq(&current->sighand->siglock);
> put_pid(current->signal->tty_old_pgrp);
> current->signal->tty_old_pgrp = NULL;
> spin_unlock_irq(&current->sighand->siglock);
>
> spin_lock_irq(&p->sighand->siglock);
> ...
> p->signal->tty = NULL;
> ...
> spin_unlock_irq(&p->sighand->siglock);
>
> tty = get_current_tty();
> // tty NULL, goto else branch by accident.
> if (tty) {
> ...
> put_pid(tty_session);
> put_pid(tty_pgrp);
> ...
> } else {
> print msg
> }
>
> in task[dumpsys], in disassociate_ctty(), tty is set NULL by
> task[adbd], tty_signal_session_leader(), then it goto else branch and
> lack of put_pid(), cause memleak.
>
> move spin_unlock(sighand->siglock) after get_current_tty() can avoid
> the race and fix the memleak.
>
> Change-Id: Ic960dda039c8f99aad3e0f4d176489a966c62f6a

Why is this line here?

2014-04-15 02:55:26

by Liu, Chuansheng

Subject: RE: [PATCH] [PATCH V2] tty: memleak in alloc_pid

> > Change-Id: Ic960dda039c8f99aad3e0f4d176489a966c62f6a
>
> Why is this line here?

Tingjie, Greg is asking you the sentence of "Change-Id", which is not
needed, please remove it with one new patch.

2014-04-15 03:02:47

by Chen Tingjie

Subject: RE: [PATCH] [PATCH V2] tty: memleak in alloc_pid

> > Change-Id: Ic960dda039c8f99aad3e0f4d176489a966c62f6a
> >
> > Why is this line here?

> Tingjie, Greg is asking you the sentence of "Change-Id", which is not needed, please remove it with one new patch.

Sorry for mistaken, I will make a new patch for it.