In each function, the value apcm is stored in the private_data field of runtime. At the same time the function ct_atc_pcm_free_substream is stored in the private_free field of the same structure. ct_atc_pcm_free_substream dereferences and ultimately frees the value in the private_data field. But each function can exit in an error case with apcm having been freed, in which case a subsequent call to the private_free function would perform a dereference after free. On the other hand, if the private_free field is not initialized, it is NULL, and not invoked (see snd_pcm_detach_substream in sound/core/pcm.c). To avoid the introduction of a dangling pointer, the initializations of the private_data and private_free fields are moved to the end of the function, past any possible free of apcm. This is safe because the previous calls to snd_pcm_hw_constraint_integer and snd_pcm_hw_constraint_minmax, which take runtime as an argument, do not refer to either of these fields.
In each function, there is one error case where apcm needs to be freed, and a call to kfree is added.
The sematic match that finds this problem is as follows: (http://coccinelle.lip6.fr/)
// <smpl> @@ expression e,e1,e2,e3; identifier f,free1,free2; expression a; @@
*e->f = a ... when != e->f = e1 when any if (...) { ... when != free1(...,e,...) when != e->f = e2 * kfree(a) ... when != free2(...,e,...) when != e->f = e3 } // </smpl>
Signed-off-by: Julia Lawall julia@diku.dk
--- sound/pci/ctxfi/ctpcm.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/sound/pci/ctxfi/ctpcm.c b/sound/pci/ctxfi/ctpcm.c index 85ab43e..457d211 100644 --- a/sound/pci/ctxfi/ctpcm.c +++ b/sound/pci/ctxfi/ctpcm.c @@ -129,8 +129,6 @@ static int ct_pcm_playback_open(struct snd_pcm_substream *substream)
apcm->substream = substream; apcm->interrupt = ct_atc_pcm_interrupt; - runtime->private_data = apcm; - runtime->private_free = ct_atc_pcm_free_substream; if (IEC958 == substream->pcm->device) { runtime->hw = ct_spdif_passthru_playback_hw; atc->spdif_out_passthru(atc, 1); @@ -155,8 +153,12 @@ static int ct_pcm_playback_open(struct snd_pcm_substream *substream) }
apcm->timer = ct_timer_instance_new(atc->timer, apcm); - if (!apcm->timer) + if (!apcm->timer) { + kfree(apcm); return -ENOMEM; + } + runtime->private_data = apcm; + runtime->private_free = ct_atc_pcm_free_substream;
return 0; } @@ -278,8 +280,6 @@ static int ct_pcm_capture_open(struct snd_pcm_substream *substream) apcm->started = 0; apcm->substream = substream; apcm->interrupt = ct_atc_pcm_interrupt; - runtime->private_data = apcm; - runtime->private_free = ct_atc_pcm_free_substream; runtime->hw = ct_pcm_capture_hw; runtime->hw.rate_max = atc->rsr * atc->msr;
@@ -298,8 +298,12 @@ static int ct_pcm_capture_open(struct snd_pcm_substream *substream) }
apcm->timer = ct_timer_instance_new(atc->timer, apcm); - if (!apcm->timer) + if (!apcm->timer) { + kfree(apcm); return -ENOMEM; + } + runtime->private_data = apcm; + runtime->private_free = ct_atc_pcm_free_substream;
return 0; }