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fs: cachefiles: fix memory leak in cachefiles_add_cache()

Andrey Albershteyn requested to merge alberand-rh/centos-stream-9:rhel9_33111 into main

cachefiles: fix memory leak in cachefiles_add_cache()

JIRA: https://issues.redhat.com/browse/RHEL-33111 CVE: CVE-2024-26840 Tested: with reproducer

Reproducer:

#!/bin/bash

# Get rid of boot-time things like verity :)
echo scan > /sys/kernel/debug/kmemleak
echo clear > /sys/kernel/debug/kmemleak

systemctl start cachefilesd
sleep 1
systemctl stop cachefilesd
sleep 30
echo scan > /sys/kernel/debug/kmemleak
cat /sys/kernel/debug/kmemleak

commit e21a2f17566cbd64926fb8f16323972f7a064444 Author: Baokun Li libaokun1@huawei.com Date: Sat Feb 17 16:14:31 2024 +0800

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: 9ae326a69004 ("CacheFiles: A cache that backs onto a mounted filesystem")
CC: stable@vger.kernel.org
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Link: https://lore.kernel.org/r/20240217081431.796809-1-libaokun1@huawei.com
Acked-by: David Howells <dhowells@redhat.com>
Reviewed-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Andrey Albershteyn aalbersh@redhat.com

Edited by Andrey Albershteyn

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