From 4674ffe2fcad45a9b164401cc0794115702326cf Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Tue, 27 Sep 2022 19:20:25 +0200 Subject: [PATCH] perf, hw_breakpoint: Fix use-after-free if perf_event_open() fails Local testing revealed that we can trigger a use-after-free during rhashtable lookup as follows: | BUG: KASAN: use-after-free in memcmp lib/string.c:757 | Read of size 8 at addr ffff888107544dc0 by task perf-rhltable-n/1293 | | CPU: 0 PID: 1293 Comm: perf-rhltable-n Not tainted 6.0.0-rc3-00014-g85260862789c #46 | Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.0-debian-1.16.0-4 04/01/2014 | Call Trace: | | memcmp lib/string.c:757 | rhashtable_compare include/linux/rhashtable.h:577 [inline] | __rhashtable_lookup include/linux/rhashtable.h:602 [inline] | rhltable_lookup include/linux/rhashtable.h:688 [inline] | task_bp_pinned kernel/events/hw_breakpoint.c:324 | toggle_bp_slot kernel/events/hw_breakpoint.c:462 | __release_bp_slot kernel/events/hw_breakpoint.c:631 [inline] | release_bp_slot kernel/events/hw_breakpoint.c:639 | register_perf_hw_breakpoint kernel/events/hw_breakpoint.c:742 | hw_breakpoint_event_init kernel/events/hw_breakpoint.c:976 | perf_try_init_event kernel/events/core.c:11261 | perf_init_event kernel/events/core.c:11325 [inline] | perf_event_alloc kernel/events/core.c:11619 | __do_sys_perf_event_open kernel/events/core.c:12157 | do_syscall_x64 arch/x86/entry/common.c:50 [inline] | do_syscall_64 arch/x86/entry/common.c:80 | entry_SYSCALL_64_after_hwframe | | | Allocated by task 1292: | perf_event_alloc kernel/events/core.c:11505 | __do_sys_perf_event_open kernel/events/core.c:12157 | do_syscall_x64 arch/x86/entry/common.c:50 [inline] | do_syscall_64 arch/x86/entry/common.c:80 | entry_SYSCALL_64_after_hwframe | | Freed by task 1292: | perf_event_alloc kernel/events/core.c:11716 | __do_sys_perf_event_open kernel/events/core.c:12157 | do_syscall_x64 arch/x86/entry/common.c:50 [inline] | do_syscall_64 arch/x86/entry/common.c:80 | entry_SYSCALL_64_after_hwframe | | The buggy address belongs to the object at ffff888107544c00 | which belongs to the cache perf_event of size 1352 | The buggy address is located 448 bytes inside of | 1352-byte region [ffff888107544c00, ffff888107545148) This happens because the first perf_event_open() managed to reserve a HW breakpoint slot, however, later fails for other reasons and returns. The second perf_event_open() runs concurrently, and during rhltable_lookup() looks up an entry which is being freed: since rhltable_lookup() may run concurrently (under the RCU read lock) with rhltable_remove(), we may end up with a stale entry, for which memory may also have already been freed when being accessed. To fix, only free the failed perf_event after an RCU grace period. This allows subsystems that store references to an event to always access it concurrently under the RCU read lock, even if initialization will fail. Given failure is unlikely and a slow-path, turning the immediate free into a call_rcu()-wrapped free does not affect performance elsewhere. Fixes: 0370dc314df3 ("perf/hw_breakpoint: Optimize list of per-task breakpoints") Reported-by: syzkaller Signed-off-by: Marco Elver Signed-off-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/20220927172025.1636995-1-elver@google.com --- kernel/events/core.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 04e19a8..e1ffdb8 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -11734,11 +11734,9 @@ err_pmu: event->destroy(event); module_put(pmu->module); err_ns: - if (event->ns) - put_pid_ns(event->ns); if (event->hw.target) put_task_struct(event->hw.target); - kmem_cache_free(perf_event_cache, event); + call_rcu(&event->rcu_head, free_event_rcu); return ERR_PTR(err); } -- 2.7.4