Re: [PATCH] media: dvb-core: Fix a possible null-pointer dereference due to data race in dvbdmx_write()
From: Dan Carpenter
Date: Thu Nov 09 2023 - 03:02:20 EST
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@xxxxxxxxx/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20231109/202311090845.BlIvG8kE-lkp@xxxxxxxxx/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@xxxxxxxxx>
| Reported-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
| Closes: https://lore.kernel.org/r/202311090845.BlIvG8kE-lkp@xxxxxxxxx/
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 }
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