[lvc-project] [PATCH 6.1] fscache: delete fscache_cookie_lru_timer when fscache exits to avoid UAF

[Vasiliy Kovalev]

From: Baokun Li <libaokun1 at huawei.com>

commit 72a6e22c604c95ddb3b10b5d3bb85b6ff4dbc34f upstream.

The fscache_cookie_lru_timer is initialized when the fscache module
is inserted, but is not deleted when the fscache module is removed.
If timer_reduce() is called before removing the fscache module,
the fscache_cookie_lru_timer will be added to the timer list of
the current cpu. Afterwards, a use-after-free will be triggered
in the softIRQ after removing the fscache module, as follows:

==================================================================
BUG: unable to handle page fault for address: fffffbfff803c9e9
 PF: supervisor read access in kernel mode
 PF: error_code(0x0000) - not-present page
PGD 21ffea067 P4D 21ffea067 PUD 21ffe6067 PMD 110a7c067 PTE 0
Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 1 UID: 0 PID: 0 Comm: swapper/1 Tainted: G W 6.11.0-rc3 #855
Tainted: [W]=WARN
RIP: 0010:__run_timer_base.part.0+0x254/0x8a0
Call Trace:
 <IRQ>
 tmigr_handle_remote_up+0x627/0x810
 __walk_groups.isra.0+0x47/0x140
 tmigr_handle_remote+0x1fa/0x2f0
 handle_softirqs+0x180/0x590
 irq_exit_rcu+0x84/0xb0
 sysvec_apic_timer_interrupt+0x6e/0x90
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20
RIP: 0010:default_idle+0xf/0x20
 default_idle_call+0x38/0x60
 do_idle+0x2b5/0x300
 cpu_startup_entry+0x54/0x60
 start_secondary+0x20d/0x280
 common_startup_64+0x13e/0x148
 </TASK>
Modules linked in: [last unloaded: netfs]
==================================================================

Therefore delete fscache_cookie_lru_timer when removing the fscahe module.

Fixes: 12bb21a29c19 ("fscache: Implement cookie user counting and resource pinning")
Cc: stable at kernel.org
Signed-off-by: Baokun Li <libaokun1 at huawei.com>
Link: https://lore.kernel.org/r/20240826112056.2458299-1-libaokun@huaweicloud.com
Acked-by: David Howells <dhowells at redhat.com>
Signed-off-by: Christian Brauner <brauner at kernel.org>
[kovalev: use the `del_timer_sync()` call instead of `timer_shutdown_sync()`]
Signed-off-by: Vasiliy Kovalev <kovalev at altlinux.org>
---
Backport to fix CVE-2024-46786
Link: https://www.cve.org/CVERecord/?id=CVE-2024-46786
---
 fs/fscache/main.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/fscache/main.c b/fs/fscache/main.c
index dad85fd84f6f9f..dc37c9df3bef7d 100644
--- a/fs/fscache/main.c
+++ b/fs/fscache/main.c
@@ -114,6 +114,7 @@ static void __exit fscache_exit(void)
 
 	kmem_cache_destroy(fscache_cookie_jar);
 	fscache_proc_cleanup();
+	del_timer_sync(&fscache_cookie_lru_timer);
 	destroy_workqueue(fscache_wq);
 	pr_notice("Unloaded\n");
 }
-- 
2.33.8