keys: Implement update for the big_key type

Implement the ->update op for the big_key type.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Jason A. Donenfeld <Jason@zx2c4.com>

KEYS: Don't write out to userspace while holding key semaphore

A lockdep circular locking dependency report was seen when running a
keyutils test:

[12537.027242] ======================================================
[12537.059309] WARNING: possible circular locking dependency detected
[12537.088148] 4.18.0-147.7.1.el8_1.x86_64+debug #1 Tainted: G OE --------- - -
[12537.125253] ------------------------------------------------------
[12537.153189] keyctl/25598 is trying to acquire lock:
[12537.175087] 000000007c39f96c (&mm->mmap_sem){++++}, at: __might_fault+0xc4/0x1b0
[12537.208365]
[12537.208365] but task is already holding lock:
[12537.234507] 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12537.270476]
[12537.270476] which lock already depends on the new lock.
[12537.270476]
[12537.307209]
[12537.307209] the existing dependency chain (in reverse order) is:
[12537.340754]
[12537.340754] -> #3 (&type->lock_class){++++}:
[12537.367434] down_write+0x4d/0x110
[12537.385202] __key_link_begin+0x87/0x280
[12537.405232] request_key_and_link+0x483/0xf70
[12537.427221] request_key+0x3c/0x80
[12537.444839] dns_query+0x1db/0x5a5 [dns_resolver]
[12537.468445] dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.496731] cifs_reconnect+0xe04/0x2500 [cifs]
[12537.519418] cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.546263] cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.573551] cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.601045] kthread+0x30c/0x3d0
[12537.617906] ret_from_fork+0x3a/0x50
[12537.636225]
[12537.636225] -> #2 (root_key_user.cons_lock){+.+.}:
[12537.664525] __mutex_lock+0x105/0x11f0
[12537.683734] request_key_and_link+0x35a/0xf70
[12537.705640] request_key+0x3c/0x80
[12537.723304] dns_query+0x1db/0x5a5 [dns_resolver]
[12537.746773] dns_resolve_server_name_to_ip+0x1e1/0x4d0 [cifs]
[12537.775607] cifs_reconnect+0xe04/0x2500 [cifs]
[12537.798322] cifs_readv_from_socket+0x461/0x690 [cifs]
[12537.823369] cifs_read_from_socket+0xa0/0xe0 [cifs]
[12537.847262] cifs_demultiplex_thread+0x311/0x2db0 [cifs]
[12537.873477] kthread+0x30c/0x3d0
[12537.890281] ret_from_fork+0x3a/0x50
[12537.908649]
[12537.908649] -> #1 (&tcp_ses->srv_mutex){+.+.}:
[12537.935225] __mutex_lock+0x105/0x11f0
[12537.954450] cifs_call_async+0x102/0x7f0 [cifs]
[12537.977250] smb2_async_readv+0x6c3/0xc90 [cifs]
[12538.000659] cifs_readpages+0x120a/0x1e50 [cifs]
[12538.023920] read_pages+0xf5/0x560
[12538.041583] __do_page_cache_readahead+0x41d/0x4b0
[12538.067047] ondemand_readahead+0x44c/0xc10
[12538.092069] filemap_fault+0xec1/0x1830
[12538.111637] __do_fault+0x82/0x260
[12538.129216] do_fault+0x419/0xfb0
[12538.146390] __handle_mm_fault+0x862/0xdf0
[12538.167408] handle_mm_fault+0x154/0x550
[12538.187401] __do_page_fault+0x42f/0xa60
[12538.207395] do_page_fault+0x38/0x5e0
[12538.225777] page_fault+0x1e/0x30
[12538.243010]
[12538.243010] -> #0 (&mm->mmap_sem){++++}:
[12538.267875] lock_acquire+0x14c/0x420
[12538.286848] __might_fault+0x119/0x1b0
[12538.306006] keyring_read_iterator+0x7e/0x170
[12538.327936] assoc_array_subtree_iterate+0x97/0x280
[12538.352154] keyring_read+0xe9/0x110
[12538.370558] keyctl_read_key+0x1b9/0x220
[12538.391470] do_syscall_64+0xa5/0x4b0
[12538.410511] entry_SYSCALL_64_after_hwframe+0x6a/0xdf
[12538.435535]
[12538.435535] other info that might help us debug this:
[12538.435535]
[12538.472829] Chain exists of:
[12538.472829] &mm->mmap_sem --> root_key_user.cons_lock --> &type->lock_class
[12538.472829]
[12538.524820] Possible unsafe locking scenario:
[12538.524820]
[12538.551431] CPU0 CPU1
[12538.572654] ---- ----
[12538.595865] lock(&type->lock_class);
[12538.613737] lock(root_key_user.cons_lock);
[12538.644234] lock(&type->lock_class);
[12538.672410] lock(&mm->mmap_sem);
[12538.687758]
[12538.687758] *** DEADLOCK ***
[12538.687758]
[12538.714455] 1 lock held by keyctl/25598:
[12538.732097] #0: 000000003de5b58d (&type->lock_class){++++}, at: keyctl_read_key+0x15a/0x220
[12538.770573]
[12538.770573] stack backtrace:
[12538.790136] CPU: 2 PID: 25598 Comm: keyctl Kdump: loaded Tainted: G
[12538.844855] Hardware name: HP ProLiant DL360 Gen9/ProLiant DL360 Gen9, BIOS P89 12/27/2015
[12538.881963] Call Trace:
[12538.892897] dump_stack+0x9a/0xf0
[12538.907908] print_circular_bug.isra.25.cold.50+0x1bc/0x279
[12538.932891] ? save_trace+0xd6/0x250
[12538.948979] check_prev_add.constprop.32+0xc36/0x14f0
[12538.971643] ? keyring_compare_object+0x104/0x190
[12538.992738] ? check_usage+0x550/0x550
[12539.009845] ? sched_clock+0x5/0x10
[12539.025484] ? sched_clock_cpu+0x18/0x1e0
[12539.043555] __lock_acquire+0x1f12/0x38d0
[12539.061551] ? trace_hardirqs_on+0x10/0x10
[12539.080554] lock_acquire+0x14c/0x420
[12539.100330] ? __might_fault+0xc4/0x1b0
[12539.119079] __might_fault+0x119/0x1b0
[12539.135869] ? __might_fault+0xc4/0x1b0
[12539.153234] keyring_read_iterator+0x7e/0x170
[12539.172787] ? keyring_read+0x110/0x110
[12539.190059] assoc_array_subtree_iterate+0x97/0x280
[12539.211526] keyring_read+0xe9/0x110
[12539.227561] ? keyring_gc_check_iterator+0xc0/0xc0
[12539.249076] keyctl_read_key+0x1b9/0x220
[12539.266660] do_syscall_64+0xa5/0x4b0
[12539.283091] entry_SYSCALL_64_after_hwframe+0x6a/0xdf

One way to prevent this deadlock scenario from happening is to not
allow writing to userspace while holding the key semaphore. Instead,
an internal buffer is allocated for getting the keys out from the
read method first before copying them out to userspace without holding
the lock.

That requires taking out the __user modifier from all the relevant
read methods as well as additional changes to not use any userspace
write helpers. That is,

1) The put_user() call is replaced by a direct copy.
2) The copy_to_user() call is replaced by memcpy().
3) All the fault handling code is removed.

Compiling on a x86-64 system, the size of the rxrpc_read() function is
reduced from 3795 bytes to 2384 bytes with this patch.

Fixes: ^1da177e4c3f4 ("Linux-2.6.12-rc2")
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>

treewide: Replace GPLv2 boilerplate/reference with SPDX - rule 152

Based on 1 normalized pattern(s):

this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version

extracted by the scancode license scanner the SPDX license identifier

GPL-2.0-or-later

has been chosen to replace the boilerplate/reference in 3029 file(s).

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190527070032.746973796@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

KEYS: big_key: Use key preparsing

Make use of key preparsing in the big key type so that quota size determination
can take place prior to keyring locking when a key is being added.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Steve Dickson <steved@redhat.com>

KEYS: Implement a big key type that can save to tmpfs

Implement a big key type that can save its contents to tmpfs and thus
swapspace when memory is tight. This is useful for Kerberos ticket caches.

Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Simo Sorce <simo@redhat.com>