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Subject[PATCH 1/2] drivers/media/dvb-core/en50221: use kref to manage struct dvb_ca_private
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Don't free the object until the file handle has been closed.  Fixes
use-after-free bug which occurs when I disconnect my DVB-S received
while VDR is running.

This is a crash dump of such a use-after-free:

general protection fault: 0000 [#1] SMP
CPU: 0 PID: 2541 Comm: CI adapter on d Not tainted 4.7.0-rc1-hosting+ #49
Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
task: ffff880027d7ce00 ti: ffff88003d8f8000 task.ti: ffff88003d8f8000
RIP: 0010:[<ffffffff812f3d1f>] [<ffffffff812f3d1f>] dvb_ca_en50221_io_read_condition.isra.7+0x6f/0x150
RSP: 0018:ffff88003d8fba98 EFLAGS: 00010206
RAX: 0000000059534255 RBX: 000000753d470f90 RCX: ffff88003c74d181
RDX: 00000001bea04ba9 RSI: ffff88003d8fbaf4 RDI: 3a3030a56d763fc0
RBP: ffff88003d8fbae0 R08: ffff88003c74d180 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff88003c480e00
R13: 00000000ffffffff R14: 0000000059534255 R15: 0000000000000000
FS: 00007fb4209b4700(0000) GS:ffff88003fc00000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f06445f4078 CR3: 000000003c55b000 CR4: 00000000000006b0
Stack:
ffff88003d8fbaf4 000000003c2170c0 0000000000004000 0000000000000000
ffff88003c480e00 ffff88003d8fbc80 ffff88003c74d180 ffff88003d8fbb8c
0000000000000000 ffff88003d8fbb10 ffffffff812f3e37 ffff88003d8fbb00
Call Trace:
[<ffffffff812f3e37>] dvb_ca_en50221_io_poll+0x37/0xa0
[<ffffffff8113109b>] do_sys_poll+0x2db/0x520

This is a backtrace of the kernel attempting to lock a freed mutex:

#0 0xffffffff81083d40 in rep_nop () at ./arch/x86/include/asm/processor.h:569
#1 cpu_relax () at ./arch/x86/include/asm/processor.h:574
#2 virt_spin_lock (lock=<optimized out>) at ./arch/x86/include/asm/qspinlock.h:57
#3 native_queued_spin_lock_slowpath (lock=0xffff88003c480e90, val=761492029) at kernel/locking/qspinlock.c:304
#4 0xffffffff810d1a06 in pv_queued_spin_lock_slowpath (val=<optimized out>, lock=<optimized out>) at ./arch/x86/include/asm/paravirt.h:669
#5 queued_spin_lock_slowpath (val=<optimized out>, lock=<optimized out>) at ./arch/x86/include/asm/qspinlock.h:28
#6 queued_spin_lock (lock=<optimized out>) at include/asm-generic/qspinlock.h:107
#7 __mutex_lock_common (use_ww_ctx=<optimized out>, ww_ctx=<optimized out>, ip=<optimized out>, nest_lock=<optimized out>, subclass=<optimized out>,
state=<optimized out>, lock=<optimized out>) at kernel/locking/mutex.c:526
#8 mutex_lock_interruptible_nested (lock=0xffff88003c480e88, subclass=<optimized out>) at kernel/locking/mutex.c:647
#9 0xffffffff812f49fe in dvb_ca_en50221_io_do_ioctl (file=<optimized out>, cmd=761492029, parg=0x1 <irq_stack_union+1>)
at drivers/media/dvb-core/dvb_ca_en50221.c:1210
#10 0xffffffff812ee660 in dvb_usercopy (file=<optimized out>, cmd=761492029, arg=<optimized out>, func=<optimized out>) at drivers/media/dvb-core/dvbdev.c:883
#11 0xffffffff812f3410 in dvb_ca_en50221_io_ioctl (file=<optimized out>, cmd=<optimized out>, arg=<optimized out>) at drivers/media/dvb-core/dvb_ca_en50221.c:1284
#12 0xffffffff8112eddd in vfs_ioctl (arg=<optimized out>, cmd=<optimized out>, filp=<optimized out>) at fs/ioctl.c:43
#13 do_vfs_ioctl (filp=0xffff88003c480e90, fd=<optimized out>, cmd=<optimized out>, arg=<optimized out>) at fs/ioctl.c:674
#14 0xffffffff8112f30c in SYSC_ioctl (arg=<optimized out>, cmd=<optimized out>, fd=<optimized out>) at fs/ioctl.c:689
#15 SyS_ioctl (fd=6, cmd=2148298626, arg=140734533693696) at fs/ioctl.c:680
#16 0xffffffff8103feb2 in entry_SYSCALL_64 () at arch/x86/entry/entry_64.S:207

Signed-off-by: Max Kellermann <max@duempel.org>
---
drivers/media/dvb-core/dvb_ca_en50221.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/drivers/media/dvb-core/dvb_ca_en50221.c b/drivers/media/dvb-core/dvb_ca_en50221.c
index b1e3a26..b5b5b19 100644
--- a/drivers/media/dvb-core/dvb_ca_en50221.c
+++ b/drivers/media/dvb-core/dvb_ca_en50221.c
@@ -123,6 +123,7 @@ struct dvb_ca_slot {

/* Private CA-interface information */
struct dvb_ca_private {
+ struct kref refcount;

/* pointer back to the public data structure */
struct dvb_ca_en50221 *pub;
@@ -173,6 +174,22 @@ static void dvb_ca_private_free(struct dvb_ca_private *ca)
kfree(ca);
}

+static void dvb_ca_private_release(struct kref *ref)
+{
+ struct dvb_ca_private *ca = container_of(ref, struct dvb_ca_private, refcount);
+ dvb_ca_private_free(ca);
+}
+
+static void dvb_ca_private_get(struct dvb_ca_private *ca)
+{
+ kref_get(&ca->refcount);
+}
+
+static void dvb_ca_private_put(struct dvb_ca_private *ca)
+{
+ kref_put(&ca->refcount, dvb_ca_private_release);
+}
+
static void dvb_ca_en50221_thread_wakeup(struct dvb_ca_private *ca);
static int dvb_ca_en50221_read_data(struct dvb_ca_private *ca, int slot, u8 * ebuf, int ecount);
static int dvb_ca_en50221_write_data(struct dvb_ca_private *ca, int slot, u8 * ebuf, int ecount);
@@ -1570,6 +1587,8 @@ static int dvb_ca_en50221_io_open(struct inode *inode, struct file *file)
dvb_ca_en50221_thread_update_delay(ca);
dvb_ca_en50221_thread_wakeup(ca);

+ dvb_ca_private_get(ca);
+
return 0;
}

@@ -1598,6 +1617,8 @@ static int dvb_ca_en50221_io_release(struct inode *inode, struct file *file)

module_put(ca->pub->owner);

+ dvb_ca_private_put(ca);
+
return err;
}

@@ -1693,6 +1714,7 @@ int dvb_ca_en50221_init(struct dvb_adapter *dvb_adapter,
ret = -ENOMEM;
goto exit;
}
+ kref_init(&ca->refcount);
ca->pub = pubca;
ca->flags = flags;
ca->slot_count = slot_count;
@@ -1772,6 +1794,6 @@ void dvb_ca_en50221_release(struct dvb_ca_en50221 *pubca)
for (i = 0; i < ca->slot_count; i++) {
dvb_ca_en50221_slot_shutdown(ca, i);
}
- dvb_ca_private_free(ca);
+ dvb_ca_private_put(ca);
pubca->private = NULL;
}
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