cachefiles: fix memory leak in cachefiles_add_cache()

The following memory leak was reported after unbinding /dev/cachefiles:

==================================================================
unreferenced object 0xffff9b674176e3c0 (size 192):
  comm "cachefilesd2", pid 680, jiffies 4294881224
  hex dump (first 32 bytes):
    01 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
  backtrace (crc ea38a44b):
    [<ffffffff8eb8a1a5>] kmem_cache_alloc+0x2d5/0x370
    [<ffffffff8e917f86>] prepare_creds+0x26/0x2e0
    [<ffffffffc002eeef>] cachefiles_determine_cache_security+0x1f/0x120
    [<ffffffffc00243ec>] cachefiles_add_cache+0x13c/0x3a0
    [<ffffffffc0025216>] cachefiles_daemon_write+0x146/0x1c0
    [<ffffffff8ebc4a3b>] vfs_write+0xcb/0x520
    [<ffffffff8ebc5069>] ksys_write+0x69/0xf0
    [<ffffffff8f6d4662>] do_syscall_64+0x72/0x140
    [<ffffffff8f8000aa>] entry_SYSCALL_64_after_hwframe+0x6e/0x76
==================================================================

Put the reference count of cache_cred in cachefiles_daemon_unbind() to
fix the problem. And also put cache_cred in cachefiles_add_cache() error
branch to avoid memory leaks.

Fixes: 9ae326a ("CacheFiles: A cache that backs onto a mounted filesystem")
CC: [email protected]
Signed-off-by: Baokun Li <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Acked-by: David Howells <[email protected]>
Reviewed-by: Jingbo Xu <[email protected]>
Reviewed-by: Jeff Layton <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: LiBaokun96

fs/cachefiles/cache.c

@@ -168,6 +168,8 @@ int cachefiles_add_cache(struct cachefiles_cache *cache)
 	dput(root);
 error_open_root:
 	cachefiles_end_secure(cache, saved_cred);
+	put_cred(cache->cache_cred);
+	cache->cache_cred = NULL;
 error_getsec:
 	fscache_relinquish_cache(cache_cookie);
 	cache->cache = NULL;

fs/cachefiles/daemon.c

@@ -816,6 +816,7 @@ static void cachefiles_daemon_unbind(struct cachefiles_cache *cache)
 	cachefiles_put_directory(cache->graveyard);
 	cachefiles_put_directory(cache->store);
 	mntput(cache->mnt);
+	put_cred(cache->cache_cred);
 
 	kfree(cache->rootdirname);
 	kfree(cache->secctx);