smb: client: fix one-byte OOB read in smb2_parse_native_symlink()

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

smb: client: fix one-byte OOB read in smb2_parse_native_symlink()

When parsing a share-root relative native symlink, memcpy copies
smb_target+1 (skipping the leading separator) but uses
strlen(smb_target)+1 as the length, reading one byte past the
allocated buffer.

This fixes the following KASAN splat when accessing an SMB symlink
with a target of '\a\b':

BUG: KASAN: slab-out-of-bounds in smb2_parse_native_symlink+0x4f5/0xca0
Read of size 5 at addr ffff88800878fe21 by task netfsfuzz-execu/1
CPU: 1 UID: 0 PID: 1 Comm: netfsfuzz-execu Tainted: G N
7.2.0-11943-g2709dd5ae32f-dirty #1 PREEMPT(lazy)
Hardware name: QEMU Ubuntu 24.04 PC v2 (i440FX + PIIX, arch_caps fix,
1996)
Call Trace:
<TASK>
dump_stack_lvl+0x7b/0xa0
print_report+0xd0/0x630
kasan_report+0xe5/0x120
kasan_check_range+0x105/0x1b0
__asan_memcpy+0x23/0x60
smb2_parse_native_symlink+0x4f5/0xca0
parse_reparse_point+0x68a/0x1530
reparse_info_to_fattr+0x752/0xa20
cifs_get_fattr+0x873/0x15b0
cifs_get_inode_info+0xc0/0x310
cifs_lookup+0x308/0xa70
__lookup_slow+0x122/0x2b0
lookup_slow+0x50/0x70
path_lookupat+0x525/0xaf0
filename_lookup+0x1f2/0x550
vfs_statx+0xd1/0x1a0
vfs_fstatat+0x65/0xc0
__do_sys_newfstatat+0x9a/0x120
do_syscall_64+0xdd/0x4a0
entry_SYSCALL_64_after_hwframe+0x77/0x7f