afs: Set vllist to NULL if addr parsing fails

afs: Set vllist to NULL if addr parsing fails

syzbot reported a bug in in afs_put_vlserverlist.

  kAFS: bad VL server IP address
  BUG: unable to handle page fault for address: fffffffffffffffa
  ...
  Oops: Oops: 0002 [#1] SMP KASAN PTI
  ...
  RIP: 0010:refcount_dec_and_test include/linux/refcount.h:450 [inline]
  RIP: 0010:afs_put_vlserverlist+0x3a/0x220 fs/afs/vl_list.c:67
  ...
  Call Trace:
   <TASK>
   afs_alloc_cell fs/afs/cell.c:218 [inline]
   afs_lookup_cell+0x12a5/0x1680 fs/afs/cell.c:264
   afs_cell_init+0x17a/0x380 fs/afs/cell.c:386
   afs_proc_rootcell_write+0x21f/0x290 fs/afs/proc.c:247
   proc_simple_write+0x114/0x1b0 fs/proc/generic.c:825
   pde_write fs/proc/inode.c:330 [inline]
   proc_reg_write+0x23d/0x330 fs/proc/inode.c:342
   vfs_write+0x25c/0x1180 fs/read_write.c:682
   ksys_write+0x12a/0x240 fs/read_write.c:736
   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
   do_syscall_64+0xcd/0x260 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f

Because afs_parse_text_addrs() parses incorrectly, its return value -EINVAL
is assigned to vllist, which results in -EINVAL being used as the vllist
address when afs_put_vlserverlist() is executed.

Set the vllist value to NULL when a parsing error occurs to avoid this
issue.

Fixes: e2c2cb8ef07a ("afs: Simplify cell record handling")
Reported-by: syzbot+5c042fbab0b292c98fc6@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5c042fbab0b292c98fc6
Tested-by: syzbot+5c042fbab0b292c98fc6@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/4119365.1753108011@warthog.procyon.org.uk
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>