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SubjectRe: [PATVH] media, dvb, IX2505V: Remember to free allocated memory in failure path (ix2505v_attach()).
On Fri, 31 Dec 2010, Malcolm Priestley wrote:

> On Fri, 2010-12-31 at 15:51 +0100, Jesper Juhl wrote:
> > On Fri, 31 Dec 2010, Malcolm Priestley wrote:
> >
> > > On Fri, 2010-12-31 at 00:11 +0100, Jesper Juhl wrote:
> > > > Hi,
> > > >
> > > > We may leak the storage allocated to 'state' in
> > > > drivers/media/dvb/frontends/ix2505v.c::ix2505v_attach() on error.
> > > > This patch makes sure we free the allocated memory in the failure case.
> > > >
> > > >
> > > > Signed-off-by: Jesper Juhl <jj@chaosbits.net>
> > > > ---
> > > > ix2505v.c | 1 +
> > > > 1 file changed, 1 insertion(+)
> > > >
> > > > Compile tested only.
> > > >
> > > > diff --git a/drivers/media/dvb/frontends/ix2505v.c b/drivers/media/dvb/frontends/ix2505v.c
> > > > index 55f2eba..fcb173d 100644
> > > > --- a/drivers/media/dvb/frontends/ix2505v.c
> > > > +++ b/drivers/media/dvb/frontends/ix2505v.c
> > > > @@ -293,6 +293,7 @@ struct dvb_frontend *ix2505v_attach(struct dvb_frontend *fe,
> > > > ret = ix2505v_read_status_reg(state);
> > > >
> > > > if (ret & 0x80) {
> > > > + kfree(state);
> > > > deb_i2c("%s: No IX2505V found\n", __func__);
> > > > goto error;
> > > > }
> > > >
> > > Memory is freed in...
> > >
> > > error:
> > > ix2505v_release(fe);
> > > return NULL;
> > >
> > > via...
> > >
> > > static int ix2505v_release(struct dvb_frontend *fe)
> > > {
> > > struct ix2505v_state *state = fe->tuner_priv;
> > >
> > > fe->tuner_priv = NULL;
> > > kfree(state);
> > >
> > > return 0;
> > > }
> > >
> >
> > Except that 'state' has not been assigned to fe->tuner_priv at this
> > point, so ix2505v_release() cannot free the memory that was just
> > allocated with kzalloc().
> >
> >
> > state is a local variable:
> > struct ix2505v_state *state = NULL;
> > ...
> >
> > we allocate memory and assign it to 'state' here:
> > state = kzalloc(sizeof(struct ix2505v_state), GFP_KERNEL);
> > if (NULL == state)
> > return NULL;
> >
> > state->config = config;
> > state->i2c = i2c;
> >
> > here 'state' is used, but not in a way that saves it anywhere:
> > if (state->config->tuner_write_only) {
> > if (fe->ops.i2c_gate_ctrl)
> > fe->ops.i2c_gate_ctrl(fe, 1);
> >
> > this function call involves 'state' but it does not save it anywhere
> > either:
> > ret = ix2505v_read_status_reg(state);
> >
> > if (ret & 0x80) {
> > deb_i2c("%s: No IX2505V found\n", __func__);
> > so when we jump to error here 'state' still exists only as the local
> > variable, it has not been assigned to anything else.
> > goto error;
> > }
> > ...
> > error:
> > there is no way this function call can free 'state' on this path since
> > it has not been assigned to fe->tuner_priv.
> > ix2505v_release(fe);
> > The local variable state goes out of scope here and leaks the memory it
> > points to:
> > return NULL;
> > }
> >
> > Am I missing something?
>
> Oh, Sorry, I see it now.
>
> Now there is two options.
>
> Either;
>
> 1) Move fe->tuner_priv = state to below line 287, so it can be released
> by ix2505v_release and fe->tuner_priv returned to NULL;
>
> 2) or not calling ix2505v_release changing line 314 to kfree(state).
> fe->tuner_priv will remain NULL through out.
>
[...]

How about this?


Signed-off-by: Jesper Juhl <jj@chaosbits.net>
---
ix2505v.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)
diff --git a/drivers/media/dvb/frontends/ix2505v.c b/drivers/media/dvb/frontends/ix2505v.c
index 55f2eba..15806e5 100644
--- a/drivers/media/dvb/frontends/ix2505v.c
+++ b/drivers/media/dvb/frontends/ix2505v.c
@@ -271,7 +271,7 @@ struct dvb_frontend *ix2505v_attach(struct dvb_frontend *fe,
const struct ix2505v_config *config,
struct i2c_adapter *i2c)
{
- struct ix2505v_state *state = NULL;
+ struct ix2505v_state *state;
int ret;

if (NULL == config) {
@@ -285,6 +285,7 @@ struct dvb_frontend *ix2505v_attach(struct dvb_frontend *fe,

state->config = config;
state->i2c = i2c;
+ fe->tuner_priv = state;

if (state->config->tuner_write_only) {
if (fe->ops.i2c_gate_ctrl)
@@ -301,8 +302,6 @@ struct dvb_frontend *ix2505v_attach(struct dvb_frontend *fe,
fe->ops.i2c_gate_ctrl(fe, 0);
}

- fe->tuner_priv = state;
-
memcpy(&fe->ops.tuner_ops, &ix2505v_tuner_ops,
sizeof(struct dvb_tuner_ops));
deb_i2c("%s: initialization (%s addr=0x%02x) ok\n",


--
Jesper Juhl <jj@chaosbits.net> http://www.chaosbits.net/
Don't top-post http://www.catb.org/~esr/jargon/html/T/top-post.html
Plain text mails only, please.



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