linux-kernel - Re: [PATCH] media: dvb-core: Fix a possible null-pointer dereference due to data race in dvbdmx

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Message-ID: <16d72edf-78de-4995-8821-e95973d5c474@kadam.mountain>
Date:   Thu, 9 Nov 2023 11:02:12 +0300
From:   Dan Carpenter <dan.carpenter@...aro.org>
To:     oe-kbuild@...ts.linux.dev, Tuo Li <islituo@...il.com>,
        mchehab@...nel.org, yongsuyoo0215@...il.com
Cc:     lkp@...el.com, oe-kbuild-all@...ts.linux.dev,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        baijiaju1990@...look.com, Tuo Li <islituo@...il.com>,
        BassCheck <bass@...a.edu.cn>
Subject: Re: [PATCH] media: dvb-core: Fix a possible null-pointer dereference
 due to data race in dvbdmx_write()

Hi Tuo,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Tuo-Li/media-dvb-core-Fix-a-possible-null-pointer-dereference-due-to-data-race-in-dvbdmx_write/20231108-200849
base:   git://linuxtv.org/media_tree.git master
patch link:    https://lore.kernel.org/r/20231108091300.3124649-1-islituo%40gmail.com
patch subject: [PATCH] media: dvb-core: Fix a possible null-pointer dereference due to data race in dvbdmx_write()
config: x86_64-randconfig-161-20231108 (https://download.01.org/0day-ci/archive/20231109/202311090845.BlIvG8kE-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20231109/202311090845.BlIvG8kE-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@...el.com>
| Reported-by: Dan Carpenter <dan.carpenter@...aro.org>
| Closes: https://lore.kernel.org/r/202311090845.BlIvG8kE-lkp@intel.com/

smatch warnings:
drivers/media/dvb-core/dvb_demux.c:1163 dvbdmx_write() warn: inconsistent returns '&dvbdemux->mutex'.

vim +1163 drivers/media/dvb-core/dvb_demux.c

947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1139  static int dvbdmx_write(struct dmx_demux *demux, const char __user *buf, size_t count)
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1140  {
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1141  	struct dvb_demux *dvbdemux = (struct dvb_demux *)demux;
947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1142  	void *p;
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1143  
eebefd4eafaa5d drivers/media/dvb-core/dvb_demux.c     Tuo Li         2023-11-08  1144  	mutex_lock(&dvbdemux->mutex);
eebefd4eafaa5d drivers/media/dvb-core/dvb_demux.c     Tuo Li         2023-11-08  1145  	if ((!demux->frontend) || (demux->frontend->source != DMX_MEMORY_FE)) {
eebefd4eafaa5d drivers/media/dvb-core/dvb_demux.c     Tuo Li         2023-11-08  1146  		mutex_unlock(&dvbdemux->mutex);
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1147  		return -EINVAL;
eebefd4eafaa5d drivers/media/dvb-core/dvb_demux.c     Tuo Li         2023-11-08  1148  	}
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1149  
c6cfe05532cf6e drivers/media/dvb/dvb-core/dvb_demux.c Julia Lawall   2010-05-22  1150  	p = memdup_user(buf, count);
c6cfe05532cf6e drivers/media/dvb/dvb-core/dvb_demux.c Julia Lawall   2010-05-22  1151  	if (IS_ERR(p))
c6cfe05532cf6e drivers/media/dvb/dvb-core/dvb_demux.c Julia Lawall   2010-05-22  1152  		return PTR_ERR(p);

Need to drop the lock before returning.

947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1153  	if (mutex_lock_interruptible(&dvbdemux->mutex)) {

Wait, what?  Why are we taking the lock a second time?  This won't work.

947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1154  		kfree(p);
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1155  		return -ERESTARTSYS;
947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1156  	}
947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1157  	dvb_dmx_swfilter(dvbdemux, p, count);
947a080037c6ae drivers/media/dvb/dvb-core/dvb_demux.c Al Viro        2008-06-22  1158  	kfree(p);
3593cab5d62c4c drivers/media/dvb/dvb-core/dvb_demux.c Ingo Molnar    2006-02-07  1159  	mutex_unlock(&dvbdemux->mutex);
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1160  
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1161  	if (signal_pending(current))
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1162  		return -EINTR;
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16 @1163  	return count;
^1da177e4c3f41 drivers/media/dvb/dvb-core/dvb_demux.c Linus Torvalds 2005-04-16  1164  }

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki