Messages in this thread Patch in this message | | | From | Tuo Li <> | Subject | [PATCH] media: dvb-core: Fix a possible null-pointer dereference due to data race in dvbdmx_write() | Date | Wed, 8 Nov 2023 17:13:00 +0800 |
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The struct field dmx_demux.frontend is often protected by the lock dvb_demux.mutex when is accessed. Here is an example in dvbdmx_connect_frontend():
mutex_lock(&dvbdemux->mutex);
demux->frontend = frontend; mutex_unlock(&dvbdemux->mutex);
However, the variable demux->frontend is accessed without holding the lock dvbdemux->mutex in dvbdmx_write():
if ((!demux->frontend) || (demux->frontend->source != DMX_MEMORY_FE))
In my opinion, this may be a harmful race, because if demux->fontend is set to NULL right after the first condition is checked, a null-pointer dereference can occur when accessing the field demux->frontend->source.
To fix this possible null-pointer dereference caused by data race, a lock and unlock pair is added when accessing the variable demux->frontend.
Reported-by: BassCheck <bass@buaa.edu.cn> Signed-off-by: Tuo Li <islituo@gmail.com> --- drivers/media/dvb-core/dvb_demux.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/drivers/media/dvb-core/dvb_demux.c b/drivers/media/dvb-core/dvb_demux.c index 7c4d86bfdd6c..791db667e2ed 100644 --- a/drivers/media/dvb-core/dvb_demux.c +++ b/drivers/media/dvb-core/dvb_demux.c @@ -1141,8 +1141,11 @@ static int dvbdmx_write(struct dmx_demux *demux, const char __user *buf, size_t struct dvb_demux *dvbdemux = (struct dvb_demux *)demux; void *p; - if ((!demux->frontend) || (demux->frontend->source != DMX_MEMORY_FE)) + mutex_lock(&dvbdemux->mutex); + if ((!demux->frontend) || (demux->frontend->source != DMX_MEMORY_FE)) { + mutex_unlock(&dvbdemux->mutex); return -EINVAL; + } p = memdup_user(buf, count); if (IS_ERR(p)) -- 2.34.1
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