ALSA: seq: Serialize compat port-info ioctls

Overview

In the Linux kernel, the following vulnerability has been resolved:

ALSA: seq: Serialize compat port-info ioctls

The native sequencer ioctl path serializes handler calls with client->ioctl_mutex, but the translated port-info compat path invokes the same handlers through snd_seq_kernel_client_ctl() without taking that mutex.

This lets concurrent compat CREATE_PORT requests pass the port-count check before any request reaches the serialized insertion. The computed integer port index can then exceed the address field range and wrap to an existing index. Subsequent subscriber teardown can resolve the duplicate address to the wrong port and access a freed subscriber.

Take ioctl_mutex while dispatching converted port-info requests, matching the native ioctl path. All translated port-info commands share this helper, so their accesses to the client port state are serialized as well.

Affected

• Linux >= b3defb791b26ea0683a93a4f49c77ec45ec96f10 < 413211dd31cb2ef2fc99fb0aa1a037a97509502c
• Linux >= b3defb791b26ea0683a93a4f49c77ec45ec96f10 < fc5c52848e405b6efb073db5035bb9ebaed11ec4
• Linux >= b3defb791b26ea0683a93a4f49c77ec45ec96f10 < 702d92f361f65d9698c473c7599d471395dc4341
• Linux >= b3defb791b26ea0683a93a4f49c77ec45ec96f10 < 95b2e0361c88753afa030c10698be0a1a5b67650
• Linux d6693160906d55ba376bf0b88b7c129762170162
• Linux 02cbce8576a31df8fca54aaec91ee081076bd79d
• Linux 6aab3aa52366a0051e5abf8aae4616c42053fd8e
• Linux f8a38ab4cd9624fc5ac8a7f965c7b20f5b62c03c
• Linux 623e5c8ae32b39cc8baea83478695dc624935318
• Linux e4ff9f294629b65df3f7982cd4faf86b2856b9d7
• Linux c3162384aed4cfe3f1a1f40041f3ba8cd7704d88
• Linux >= 3.2.99 < 3.3
• Linux >= 3.16.54 < 3.17
• Linux >= 3.18.94 < 3.19
• Linux >= 4.1.50 < 4.2
• Linux >= 4.4.115 < 4.5
• Linux >= 4.9.78 < 4.10
• Linux >= 4.14.15 < 4.15
• Linux 4.15

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.