From: Baokun Li <libaokun1@xxxxxxxxxx>
We got the following issue in our fault injection stress test:
==================================================================
BUG: KASAN: slab-use-after-free in fscache_withdraw_volume+0x2e1/0x370
Read of size 4 at addr ffff88810680be08 by task ondemand-04-dae/5798
CPU: 0 PID: 5798 Comm: ondemand-04-dae Not tainted 6.8.0-dirty #565
Call Trace:
kasan_check_range+0xf6/0x1b0
fscache_withdraw_volume+0x2e1/0x370
cachefiles_withdraw_volume+0x31/0x50
cachefiles_withdraw_cache+0x3ad/0x900
cachefiles_put_unbind_pincount+0x1f6/0x250
cachefiles_daemon_release+0x13b/0x290
__fput+0x204/0xa00
task_work_run+0x139/0x230
Allocated by task 5820:
__kmalloc+0x1df/0x4b0
fscache_alloc_volume+0x70/0x600
__fscache_acquire_volume+0x1c/0x610
erofs_fscache_register_volume+0x96/0x1a0
erofs_fscache_register_fs+0x49a/0x690
erofs_fc_fill_super+0x6c0/0xcc0
vfs_get_super+0xa9/0x140
vfs_get_tree+0x8e/0x300
do_new_mount+0x28c/0x580
[...]
Freed by task 5820:
kfree+0xf1/0x2c0
fscache_put_volume.part.0+0x5cb/0x9e0
erofs_fscache_unregister_fs+0x157/0x1b0
erofs_kill_sb+0xd9/0x1c0
deactivate_locked_super+0xa3/0x100
vfs_get_super+0x105/0x140
vfs_get_tree+0x8e/0x300
do_new_mount+0x28c/0x580
[...]
==================================================================
Following is the process that triggers the issue:
mount failed | daemon exit
------------------------------------------------------------
deactivate_locked_super cachefiles_daemon_release
erofs_kill_sb
erofs_fscache_unregister_fs
fscache_relinquish_volume
__fscache_relinquish_volume
fscache_put_volume(fscache_volume, fscache_volume_put_relinquish)
zero = __refcount_dec_and_test(&fscache_volume->ref, &ref);
cachefiles_put_unbind_pincount
cachefiles_daemon_unbind
cachefiles_withdraw_cache
cachefiles_withdraw_volumes
list_del_init(&volume->cache_link)
fscache_free_volume(fscache_volume)
cache->ops->free_volume
cachefiles_free_volume
list_del_init(&cachefiles_volume->cache_link);
kfree(fscache_volume)
cachefiles_withdraw_volume
fscache_withdraw_volume
fscache_volume->n_accesses
// fscache_volume UAF !!!
The fscache_volume in cache->volumes must not have been freed yet, but its
reference count may be 0. So use the new fscache_try_get_volume() helper
function try to get its reference count.
If the reference count of fscache_volume is 0, fscache_put_volume() is
freeing it, so wait for it to be removed from cache->volumes.
If its reference count is not 0, call cachefiles_withdraw_volume() with
reference count protection to avoid the above issue.
Fixes: fe2140e2f57f ("cachefiles: Implement volume support")
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
---
fs/cachefiles/cache.c | 10 ++++++++++
include/trace/events/fscache.h | 4 ++++
2 files changed, 14 insertions(+)
diff --git a/fs/cachefiles/cache.c b/fs/cachefiles/cache.c
index f449f7340aad..56ef519a36a0 100644
--- a/fs/cachefiles/cache.c
+++ b/fs/cachefiles/cache.c
@@ -8,6 +8,7 @@
#include <linux/slab.h>
#include <linux/statfs.h>
#include <linux/namei.h>
+#include <trace/events/fscache.h>
#include "internal.h"
/*
@@ -319,12 +320,20 @@ static void cachefiles_withdraw_volumes(struct cachefiles_cache *cache)
_enter("");
for (;;) {
+ struct fscache_volume *vcookie = NULL;
struct cachefiles_volume *volume = NULL;
spin_lock(&cache->object_list_lock);
if (!list_empty(&cache->volumes)) {
volume = list_first_entry(&cache->volumes,
struct cachefiles_volume, cache_link);
+ vcookie = fscache_try_get_volume(volume->vcookie,
+ fscache_volume_get_withdraw);
+ if (!vcookie) {
+ spin_unlock(&cache->object_list_lock);
+ cpu_relax();
+ continue;
+ }
list_del_init(&volume->cache_link);
}
spin_unlock(&cache->object_list_lock);
@@ -332,6 +341,7 @@ static void cachefiles_withdraw_volumes(struct cachefiles_cache *cache)
break;
cachefiles_withdraw_volume(volume);
+ fscache_put_volume(vcookie, fscache_volume_put_withdraw);
}
_leave("");
diff --git a/include/trace/events/fscache.h b/include/trace/events/fscache.h
index a6190aa1b406..f1a73aa83fbb 100644
--- a/include/trace/events/fscache.h
+++ b/include/trace/events/fscache.h
@@ -35,12 +35,14 @@ enum fscache_volume_trace {
fscache_volume_get_cookie,
fscache_volume_get_create_work,
fscache_volume_get_hash_collision,
+ fscache_volume_get_withdraw,
fscache_volume_free,
fscache_volume_new_acquire,
fscache_volume_put_cookie,
fscache_volume_put_create_work,
fscache_volume_put_hash_collision,
fscache_volume_put_relinquish,
+ fscache_volume_put_withdraw,
fscache_volume_see_create_work,
fscache_volume_see_hash_wake,
fscache_volume_wait_create_work,
@@ -120,12 +122,14 @@ enum fscache_access_trace {
EM(fscache_volume_get_cookie, "GET cook ") \
EM(fscache_volume_get_create_work, "GET creat") \
EM(fscache_volume_get_hash_collision, "GET hcoll") \
+ EM(fscache_volume_get_withdraw, "GET withd") \
EM(fscache_volume_free, "FREE ") \
EM(fscache_volume_new_acquire, "NEW acq ") \
EM(fscache_volume_put_cookie, "PUT cook ") \
EM(fscache_volume_put_create_work, "PUT creat") \
EM(fscache_volume_put_hash_collision, "PUT hcoll") \
EM(fscache_volume_put_relinquish, "PUT relnq") \
+ EM(fscache_volume_put_withdraw, "PUT withd") \
EM(fscache_volume_see_create_work, "SEE creat") \
EM(fscache_volume_see_hash_wake, "SEE hwake") \
E_(fscache_volume_wait_create_work, "WAIT crea")
--
2.39.2
