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authorTakashi Sakamoto <o-takashi@sakamocchi.jp>2021-04-08 19:31:49 +0900
committerTakashi Iwai <tiwai@suse.de>2021-04-08 13:31:03 +0200
commit66c6d1ef86ff3c1466e646d94c8eb3dcc9ccf873 (patch)
tree113e9c1deb0034effda776b0c4915909248da7f8 /include/sound
parent884c7094a272fb674423bd5a473caa3c714045fe (diff)
downloadlinux-66c6d1ef86ff3c1466e646d94c8eb3dcc9ccf873.tar.bz2
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 (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. Link: https://lore.kernel.org/r/s5htur3zl5e.wl-tiwai@suse.de 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> Link: https://lore.kernel.org/r/20210408103149.40357-1-o-takashi@sakamocchi.jp Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'include/sound')
-rw-r--r--include/sound/core.h2
1 files changed, 1 insertions, 1 deletions
diff --git a/include/sound/core.h b/include/sound/core.h
index 2e24f194ef70..1f9aef0adbc9 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 */