smb/client: fix memory leak in smb2_open_file()

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

smb/client: fix memory leak in smb2_open_file()

Reproducer:

1. server: directories are exported read-only

2. client: mount -t cifs //${server_ip}/export /mnt

3. client: dd if=/dev/zero of=/mnt/file bs=512 count=1000 oflag=direct

4. client: umount /mnt

5. client: sleep 1

6. client: modprobe -r cifs

The error message is as follows:

=============================================================================

BUG cifs_small_rq (Not tainted): Objects remaining on __kmem_cache_shutdown()

-----------------------------------------------------------------------------

Object 0x00000000d47521be @offset=14336

...

WARNING: mm/slub.c:1251 at __kmem_cache_shutdown+0x34e/0x440, CPU#0: modprobe/1577

...

Call Trace:

<TASK>

kmem_cache_destroy+0x94/0x190

cifs_destroy_request_bufs+0x3e/0x50 [cifs]

cleanup_module+0x4e/0x540 [cifs]

__se_sys_delete_module+0x278/0x400

__x64_sys_delete_module+0x5f/0x70

x64_sys_call+0x2299/0x2ff0

do_syscall_64+0x89/0x350

entry_SYSCALL_64_after_hwframe+0x76/0x7e

...

kmem_cache_destroy cifs_small_rq: Slab cache still has objects when called from cifs_destroy_request_bufs+0x3e/0x50 [cifs]

WARNING: mm/slab_common.c:532 at kmem_cache_destroy+0x16b/0x190, CPU#0: modprobe/1577