[PATCH] ALSA: control: expand limitation on the number of user-defined control element set per card
Takashi Iwai
tiwai at suse.de
Tue Jan 26 16:57:55 CET 2021
On Mon, 25 Jan 2021 08:09:10 +0100,
Takashi Iwai wrote:
>
> On Mon, 25 Jan 2021 01:56:19 +0100,
> Takashi Sakamoto wrote:
> >
> > When preparing for safety, we should not assume anything as long as the
> > worst case is clear, in my opinion.
> >
> > The initial maximum memory consumption is 5.2 MB. With limitation of
> > control element by control element, it's so large due to the data of TLV
> > per control element set. With limitation of control element set by control
> > element set, it's 19.7 MB and deterministic (in my patch).
> >
> > It's can be investigated to arrange relevant parameters, but it
> > certainly brings regression to the old-versioned userspace applications.
> > It would not be better to change the size of data of TLV and the number
> > of control elements in control element set.
> >
> > At first place, my request is to relax limitation according to userspace
> > application. Expansion of memory consumption is unavoidable. The linear
> > increase of memory consumption about which you mentioned is not so worse
> > as a result of compromise to the above.
>
> Hm? We really care only the *max* memory consumption case (i.e. the
> worst case scenario), not about the memory consumption in your
> particular use case. And this can be certainly accountable.
>
> Whether to calculate the amount of TLV data separately from the main
> user elements is another thing to be discussed, but in either way, we
> can know the data size at allocation time, and we can also calculate
> the theoretical max of the current implementation beforehand.
Now I counted the actual memory consumption in the old code, and this
could lead to ca 32MB without TLV and enum strings. TLV and enum
strings may attribute 6MB more total, so it can go up to 38MB.
It's really high, and we'd rather want to reduce it, instead of
increasing it.
Below is a revised patch, that calculates the memory consumption in
more details. In this patch, the max memory is reduced to 8MB --
which should be large enough for any sensible use cases. I guess this
will fulfill your requirement?
The patch also makes the limit as a module option. I'm not 100% sure
whether it's needed, but since the patch reduces the size, it might
need some cure for an extreme case.
Takashi
-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] ALSA: control: Add memory consumption limit to user controls
ALSA control interface allows users to add arbitrary control elements
(called "user controls" or "user elements"), and its resource usage is
limited just by the max number of control sets (currently 32). This
limit, however, is quite loose: each allocation of control set may
have 1028 elements, and each element may have up to 512 bytes of value
data. Moreover, each control set may contain the enum strings and TLV
data, which can be up to 64kB and 128kB, respectively. Totally, the
whole memory consumption may go over 38MB -- it's quite large, and
we'd rather like to reduce the size.
OTOH, there have been other requests even to increase the max number
of user elements; e.g. FireWire stack require the more user controls,
hence we want to raise the bar, too.
For satisfying both requirements, this patch changes the management of
user controls: instead of setting the upper limit of the number of
user controls, we check the actual memory allocation size and set the
upper limit of the total allocation in bytes. As long as the memory
consumption stays below the limit, more user controls are allowed than
the current limit 32. At the same time, we set the lower limit (8MB)
as default than the current theoretical limit, in order to lower the
risk of DoS.
As a compromise for lowering the default limit, now the actual memory
limit is defined as a module option, max_user_ctl, so that user can
increase/decrease the limit if really needed, too.
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
include/sound/core.h | 2 +-
sound/core/control.c | 66 +++++++++++++++++++++++++++++---------------
2 files changed, 44 insertions(+), 24 deletions(-)
diff --git a/include/sound/core.h b/include/sound/core.h
index 0462c577d7a3..a21b14451810 100644
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -100,7 +100,7 @@ struct snd_card {
struct rw_semaphore controls_rwsem; /* controls list lock */
rwlock_t ctl_files_rwlock; /* ctl_files list lock */
int controls_count; /* count of all controls */
- int user_ctl_count; /* count of all user controls */
+ size_t user_ctl_alloc_size; /* current memory allocation by user controls */
struct list_head controls; /* all controls for this card */
struct list_head ctl_files; /* active control files */
diff --git a/sound/core/control.c b/sound/core/control.c
index 5165741a8400..bbc4ee61f965 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -7,6 +7,7 @@
#include <linux/threads.h>
#include <linux/interrupt.h>
#include <linux/module.h>
+#include <linux/moduleparam.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/time.h>
@@ -18,10 +19,13 @@
#include <sound/info.h>
#include <sound/control.h>
-/* max number of user-defined controls */
-#define MAX_USER_CONTROLS 32
#define MAX_CONTROL_COUNT 1028
+/* Max allocation size for user controls */
+static int max_user_ctl_alloc_size = 8 * 1024 * 1024;
+module_param_named(max_user_ctl, max_user_ctl_alloc_size, int, 0444);
+MODULE_PARM_DESC(max_user_ctl, "Max allocation size for user controls");
+
struct snd_kctl_ioctl {
struct list_head list; /* list of all ioctls */
snd_kctl_ioctl_func_t fioctl;
@@ -537,9 +541,6 @@ static int snd_ctl_remove_user_ctl(struct snd_ctl_file * file,
goto error;
}
ret = snd_ctl_remove(card, kctl);
- if (ret < 0)
- goto error;
- card->user_ctl_count--;
error:
up_write(&card->controls_rwsem);
return ret;
@@ -1226,11 +1227,18 @@ struct user_element {
struct snd_card *card;
char *elem_data; /* element data */
unsigned long elem_data_size; /* size of element data in bytes */
+ size_t alloc_size; /* allocated size */
void *tlv_data; /* TLV data */
unsigned long tlv_data_size; /* TLV data size */
void *priv_data; /* private data (like strings for enumerated type) */
};
+/* check whether the addition (in bytes) of user ctl element may overflow the limit */
+static bool user_elem_overflow(struct snd_card *card, ssize_t add)
+{
+ return (ssize_t)card->user_ctl_alloc_size + add >= max_user_ctl_alloc_size;
+}
+
static int snd_ctl_elem_user_info(struct snd_kcontrol *kcontrol,
struct snd_ctl_elem_info *uinfo)
{
@@ -1309,6 +1317,10 @@ static int replace_user_tlv(struct snd_kcontrol *kctl, unsigned int __user *buf,
if (size > 1024 * 128) /* sane value */
return -EINVAL;
+ /* does the TLV size change cause overflow? */
+ if (user_elem_overflow(ue->card, (ssize_t)(size - ue->tlv_data_size)))
+ return -ENOMEM;
+
container = vmemdup_user(buf, size);
if (IS_ERR(container))
return PTR_ERR(container);
@@ -1326,11 +1338,15 @@ static int replace_user_tlv(struct snd_kcontrol *kctl, unsigned int __user *buf,
for (i = 0; i < kctl->count; ++i)
kctl->vd[i].access |= SNDRV_CTL_ELEM_ACCESS_TLV_READ;
mask = SNDRV_CTL_EVENT_MASK_INFO;
+ } else {
+ ue->card->user_ctl_alloc_size -= ue->tlv_data_size;
+ ue->tlv_data_size = 0;
+ kvfree(ue->tlv_data);
}
- kvfree(ue->tlv_data);
ue->tlv_data = container;
ue->tlv_data_size = size;
+ ue->card->user_ctl_alloc_size += size;
mask |= SNDRV_CTL_EVENT_MASK_TLV;
for (i = 0; i < kctl->count; ++i) {
@@ -1374,16 +1390,17 @@ static int snd_ctl_elem_init_enum_names(struct user_element *ue)
unsigned int i;
const uintptr_t user_ptrval = ue->info.value.enumerated.names_ptr;
- if (ue->info.value.enumerated.names_length > 64 * 1024)
+ buf_len = ue->info.value.enumerated.names_length;
+ if (buf_len > 64 * 1024)
return -EINVAL;
- names = vmemdup_user((const void __user *)user_ptrval,
- ue->info.value.enumerated.names_length);
+ if (user_elem_overflow(ue->card, buf_len))
+ return -ENOMEM;
+ names = vmemdup_user((const void __user *)user_ptrval, buf_len);
if (IS_ERR(names))
return PTR_ERR(names);
/* check that there are enough valid names */
- buf_len = ue->info.value.enumerated.names_length;
p = names;
for (i = 0; i < ue->info.value.enumerated.items; ++i) {
name_len = strnlen(p, buf_len);
@@ -1397,6 +1414,7 @@ static int snd_ctl_elem_init_enum_names(struct user_element *ue)
ue->priv_data = names;
ue->info.value.enumerated.names_ptr = 0;
+ ue->alloc_size += buf_len;
return 0;
}
@@ -1405,6 +1423,8 @@ static void snd_ctl_elem_user_free(struct snd_kcontrol *kcontrol)
{
struct user_element *ue = kcontrol->private_data;
+ ue->card->user_ctl_alloc_size -= ue->alloc_size;
+ ue->card->user_ctl_alloc_size -= ue->tlv_data_size;
kvfree(ue->tlv_data);
kvfree(ue->priv_data);
kfree(ue);
@@ -1418,6 +1438,7 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
unsigned int count;
unsigned int access;
long private_size;
+ size_t alloc_size;
struct user_element *ue;
unsigned int offset;
int err;
@@ -1435,13 +1456,6 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
return err;
}
- /*
- * The number of userspace controls are counted control by control,
- * not element by element.
- */
- if (card->user_ctl_count + 1 > MAX_USER_CONTROLS)
- return -ENOMEM;
-
/* Check the number of elements for this userspace control. */
count = info->owner;
if (count == 0)
@@ -1472,6 +1486,11 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
if (info->count < 1)
return -EINVAL;
private_size = value_sizes[info->type] * info->count;
+ alloc_size = sizeof(struct user_element) + private_size * count;
+
+ /* Check the memory allocation limit */
+ if (user_elem_overflow(card, alloc_size))
+ return -ENOMEM;
/*
* Keep memory object for this userspace control. After passing this
@@ -1483,19 +1502,22 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
if (err < 0)
return err;
memcpy(&kctl->id, &info->id, sizeof(kctl->id));
- kctl->private_data = kzalloc(sizeof(struct user_element) + private_size * count,
- GFP_KERNEL);
- if (kctl->private_data == NULL) {
+ ue = kzalloc(alloc_size, GFP_KERNEL);
+ if (!ue) {
kfree(kctl);
return -ENOMEM;
}
+ kctl->private_data = ue;
kctl->private_free = snd_ctl_elem_user_free;
+ /* increment the allocated size; decremented again at private_free */
+ card->user_ctl_alloc_size += alloc_size;
+
/* Set private data for this userspace control. */
- ue = (struct user_element *)kctl->private_data;
ue->card = card;
ue->info = *info;
ue->info.access = 0;
+ ue->alloc_size = alloc_size;
ue->elem_data = (char *)ue + sizeof(*ue);
ue->elem_data_size = private_size;
if (ue->info.type == SNDRV_CTL_ELEM_TYPE_ENUMERATED) {
@@ -1535,8 +1557,6 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file,
* which locks the element.
*/
- card->user_ctl_count++;
-
unlock:
up_write(&card->controls_rwsem);
return err;
--
2.26.2
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