Re: [PATCH RESEND] cachefiles: fix memory leak in cachefiles_add_cache()

[Jeff Layton <jlayton@kernel.org>]

On Sat, 2024-02-17 at 16:14 +0800, Baokun Li wrote:
> 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: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
> CC: stable@vger.kernel.org
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
>  fs/cachefiles/cache.c  | 2 ++
>  fs/cachefiles/daemon.c | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/fs/cachefiles/cache.c b/fs/cachefiles/cache.c
> index 7077f72e6f47..f449f7340aad 100644
> --- a/fs/cachefiles/cache.c
> +++ b/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;
> diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
> index 3f24905f4066..6465e2574230 100644
> --- a/fs/cachefiles/daemon.c
> +++ b/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);

Looks reasonable to me too. Nice catch:

Reviewed-by: Jeff Layton <jlayton@kernel.org>