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SubjectRe: [PATCH] drm/vmwgfx: Fix double free in vmw_recv_msg()
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On Thu, 2019-08-15 at 09:38 +0100, Colin Ian King wrote:
> On 15/08/2019 09:30, Dan Carpenter wrote:
> > We recently added a kfree() after the end of the loop:
> >
> > if (retries == RETRIES) {
> > kfree(reply);
> > return -EINVAL;
> > }
> >
> > There are two problems. First the test is wrong and because
> > retries
> > equals RETRIES if we succeed on the last iteration through the
> > loop.
> > Second if we fail on the last iteration through the loop then the
> > kfree
> > is a double free.
> >
> > When you're reading this code, please note the break statement at
> > the
> > end of the while loop. This patch changes the loop so that if it's
> > not
> > successful then "reply" is NULL and we can test for that afterward.
> >
> > Fixes: 6b7c3b86f0b6 ("drm/vmwgfx: fix memory leak when too many
> > retries have occurred")
> > Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
> > ---
> > drivers/gpu/drm/vmwgfx/vmwgfx_msg.c | 8 +++-----
> > 1 file changed, 3 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
> > b/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
> > index 59e9d05ab928..0af048d1a815 100644
> > --- a/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
> > +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_msg.c
> > @@ -353,7 +353,7 @@ static int vmw_recv_msg(struct rpc_channel
> > *channel, void **msg,
> > !!(HIGH_WORD(ecx) &
> > MESSAGE_STATUS_HB));
> > if ((HIGH_WORD(ebx) & MESSAGE_STATUS_SUCCESS) == 0) {
> > kfree(reply);
> > -
> > + reply = NULL;
> > if ((HIGH_WORD(ebx) & MESSAGE_STATUS_CPT) != 0)
> > {
> > /* A checkpoint occurred. Retry. */
> > continue;
> > @@ -377,7 +377,7 @@ static int vmw_recv_msg(struct rpc_channel
> > *channel, void **msg,
> >
> > if ((HIGH_WORD(ecx) & MESSAGE_STATUS_SUCCESS) == 0) {
> > kfree(reply);
> > -
> > + reply = NULL;
> > if ((HIGH_WORD(ecx) & MESSAGE_STATUS_CPT) != 0)
> > {
> > /* A checkpoint occurred. Retry. */
> > continue;
> > @@ -389,10 +389,8 @@ static int vmw_recv_msg(struct rpc_channel
> > *channel, void **msg,
> > break;
> > }
> >
> > - if (retries == RETRIES) {
> > - kfree(reply);
> > + if (!reply)
> > return -EINVAL;
> > - }
> >
> > *msg_len = reply_len;
> > *msg = reply;
> >
>
> Dan, Thanks for fixing up my mistake.

Thanks, Dan. Sorry for the late reply.
Reviewed-by: Thomas Hellström <thellstrom@vmware.com>
Will push this to fixes.

/Thomas

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