On Thu, 08 Apr 2021 12:50:25 +0200, Takashi Sakamoto wrote:
Hi,
Some supplements.
On Thu, Apr 08, 2021 at 07:31:49PM +0900, Takashi Sakamoto wrote:
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 (ILP32) or 1024 bytes (LP64) 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. ALSA 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_alloc_size', so that user can increase/decrease the limit if really needed, too.
Co-developed-by: Takashi Iwai tiwai@suse.de Reviewed-by: Takashi Sakamoto o-takashi@sakamocchi.jp Tested-by: Takashi Sakamoto o-takashi@sakamocchi.jp Signed-off-by: Takashi Sakamoto o-takashi@sakamocchi.jp
v1->v2: Drop alloc_size field from user_element, calculate at private_free v2->v3: Rebase. Fix boundary error. Obsolete macro usage relying on modern compiler optimization. Change comment style by modern coding convention. Rename module parameter so that users get it easily. Patch comment improvements.
include/sound/core.h | 2 +- sound/core/control.c | 75 ++++++++++++++++++++++++++++++-------------- 2 files changed, 52 insertions(+), 25 deletions(-)
The original content of patch comes from Iwai-san[1]. I have no clear idea to handle the case so add 'Co-developed-by' tag to the patch. If this is not good, I apologize the lack of my understanding to the development process in Linux kernel.
It depends. In some cases, you just carry the patch with the original authorship (From address) and put your sign-off. In some cases, Co-developed-by can be used. I don't mind much either way, so I took your v3 patch now (with the addition of the Link URL to v2 patch).
Thanks!
Takashi