6.6-stable review patch. If anyone has any objections, please let me know.
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From: Baokun Li libaokun1@huawei.com
[ Upstream commit 522018a0de6b6fcce60c04f86dfc5f0e4b6a1b36 ]
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@huawei.com Link: https://lore.kernel.org/r/20240628062930.2467993-3-libaokun@huaweicloud.com Signed-off-by: Christian Brauner brauner@kernel.org Signed-off-by: Baokun Li libaokun1@huawei.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/cachefiles/cache.c | 10 ++++++++++ include/trace/events/fscache.h | 4 ++++ 2 files changed, 14 insertions(+)
--- 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( _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( break;
cachefiles_withdraw_volume(volume); + fscache_put_volume(vcookie, fscache_volume_put_withdraw); }
_leave(""); --- 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")