cachefiles: fix memory leak in cachefiles_add_cache()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: 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.

References

• https://git.kernel.org/stable/c/cb5466783793e66272624cf71925ae1d1ba32083
• https://git.kernel.org/stable/c/037d5a949b0455540ef9aab34c10ddf54b65d285
• https://git.kernel.org/stable/c/43eccc5823732ba6daab2511ed32dfc545a666d8
• https://git.kernel.org/stable/c/94965be37add0983672e48ecb33cdbda92b62579
• https://git.kernel.org/stable/c/8b218e2f0a27a9f09428b1847b4580640b9d1e58
• https://git.kernel.org/stable/c/38e921616320d159336b0ffadb09e9fb4945c7c3
• https://git.kernel.org/stable/c/9cac69912052a4def571fedf1cb9bb4ec590e25a
• https://git.kernel.org/stable/c/e21a2f17566cbd64926fb8f16323972f7a064444