audit: fix exe mark UAF in kill_rules()

Overview

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

audit: fix exe mark UAF in kill_rules()

kill_rules() removes mixed AUDIT_DIR and AUDIT_EXE rules when an audit tree is pruned. It drops entry->rule.exe before removing the rule from the RCU-visible filter lists.

After a rule has been installed with AUDIT_ADD_RULE, which requires CAP_AUDIT_CONTROL, removing the watched directory can race with another task that is still evaluating the rule. In that case, fsnotify can free the executable mark before the reader reaches audit_mark_compare(), causing a use-after-free.

KASAN reports:

BUG: KASAN: slab-use-after-free in audit_mark_compare+0x8d/0xa0

Unlink the published rules from the RCU-visible lists and retain them on tree->rules for cleanup. If any rule has an executable mark, wait for a single RCU grace period before removing the marks and scheduling the entries for freeing. Otherwise, call_rcu() already provides the required deferred freeing without a synchronous wait.

Affected

• Linux >= 34d99af52ad40bd498ba66970579a5bc1fb1a3bc < 304960900991157e6883bdf0b39782b690545ee8
• Linux >= 34d99af52ad40bd498ba66970579a5bc1fb1a3bc < 88633025f20ba9c32ccdb3efc86eafdf98cb825c
• Linux >= 34d99af52ad40bd498ba66970579a5bc1fb1a3bc < f2cc5462b78559c7628a9f8ac9a9592e7783183a
• Linux >= 34d99af52ad40bd498ba66970579a5bc1fb1a3bc < aa650d87a498844060eecb1d336f4d46f4d1b0b3
• Linux 4.3

Remediation

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