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Date:   Thu, 08 Jun 2023 16:28:44 +0300
Message-Id: <CT7AZ4IW0A7I.Q01Z5CYGS9H6@suppilovahvero>
Cc:     <dhowells@redhat.com>, <keyrings@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] keys: Fix linking a duplicate key to a keyring's
 assoc_array
From:   "Jarkko Sakkinen" <jarkko@kernel.org>
To:     "Jarkko Sakkinen" <jarkko@kernel.org>,
        "Petr Pavlu" <petr.pavlu@suse.com>
References: <20230323130412.32097-1-petr.pavlu@suse.com>
 <20230330001355.dyazfwx4tyiyvux2@kernel.org>
 <b45eb4c3-77c6-d0ae-9e90-a120fcab869b@suse.com>
 <CT7AR88TXGRA.3BSYSJFL8C5LR@suppilovahvero>
In-Reply-To: <CT7AR88TXGRA.3BSYSJFL8C5LR@suppilovahvero>
Precedence: bulk

On Thu Jun 8, 2023 at 4:18 PM EEST, Jarkko Sakkinen wrote:
> On Thu Jun 8, 2023 at 12:55 PM EEST, Petr Pavlu wrote:
> > On 3/30/23 02:13, Jarkko Sakkinen wrote:
> > > On Thu, Mar 23, 2023 at 02:04:12PM +0100, Petr Pavlu wrote:
> > >> When making a DNS query inside the kernel using dns_query(), the req=
uest
> > >> code can in rare cases end up creating a duplicate index key in the
> > >> assoc_array of the destination keyring. It is eventually found by
> > >> a BUG_ON() check in the assoc_array implementation and results in
> > >> a crash.
> > >>
> > >> Example report:
> > >> [2158499.700025] kernel BUG at ../lib/assoc_array.c:652!
> > >> [2158499.700039] invalid opcode: 0000 [#1] SMP PTI
> > >> [2158499.700065] CPU: 3 PID: 31985 Comm: kworker/3:1 Kdump: loaded N=
ot tainted 5.3.18-150300.59.90-default #1 SLE15-SP3
> > >> [2158499.700096] Hardware name: VMware, Inc. VMware Virtual Platform=
/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
> > >> [2158499.700351] Workqueue: cifsiod cifs_resolve_server [cifs]
> > >> [2158499.700380] RIP: 0010:assoc_array_insert+0x85f/0xa40
> > >> [2158499.700401] Code: ff 74 2b 48 8b 3b 49 8b 45 18 4c 89 e6 48 83 =
e7 fe e8 95 ec 74 00 3b 45 88 7d db 85 c0 79 d4 0f 0b 0f 0b 0f 0b e8 41 f2 =
be ff <0f> 0b 0f 0b 81 7d 88 ff ff ff 7f 4c 89 eb 4c 8b ad 58 ff ff ff 0f
> > >> [2158499.700448] RSP: 0018:ffffc0bd6187faf0 EFLAGS: 00010282
> > >> [2158499.700470] RAX: ffff9f1ea7da2fe8 RBX: ffff9f1ea7da2fc1 RCX: 00=
00000000000005
> > >> [2158499.700492] RDX: 0000000000000000 RSI: 0000000000000005 RDI: 00=
00000000000000
> > >> [2158499.700515] RBP: ffffc0bd6187fbb0 R08: ffff9f185faf1100 R09: 00=
00000000000000
> > >> [2158499.700538] R10: ffff9f1ea7da2cc0 R11: 000000005ed8cec8 R12: ff=
ffc0bd6187fc28
> > >> [2158499.700561] R13: ffff9f15feb8d000 R14: ffff9f1ea7da2fc0 R15: ff=
ff9f168dc0d740
> > >> [2158499.700585] FS:  0000000000000000(0000) GS:ffff9f185fac0000(000=
0) knlGS:0000000000000000
> > >> [2158499.700610] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > >> [2158499.700630] CR2: 00007fdd94fca238 CR3: 0000000809d8c006 CR4: 00=
000000003706e0
> > >> [2158499.700702] Call Trace:
> > >> [2158499.700741]  ? key_alloc+0x447/0x4b0
> > >> [2158499.700768]  ? __key_link_begin+0x43/0xa0
> > >> [2158499.700790]  __key_link_begin+0x43/0xa0
> > >> [2158499.700814]  request_key_and_link+0x2c7/0x730
> > >> [2158499.700847]  ? dns_resolver_read+0x20/0x20 [dns_resolver]
> > >> [2158499.700873]  ? key_default_cmp+0x20/0x20
> > >> [2158499.700898]  request_key_tag+0x43/0xa0
> > >> [2158499.700926]  dns_query+0x114/0x2ca [dns_resolver]
> > >> [2158499.701127]  dns_resolve_server_name_to_ip+0x194/0x310 [cifs]
> > >> [2158499.701164]  ? scnprintf+0x49/0x90
> > >> [2158499.701190]  ? __switch_to_asm+0x40/0x70
> > >> [2158499.701211]  ? __switch_to_asm+0x34/0x70
> > >> [2158499.701405]  reconn_set_ipaddr_from_hostname+0x81/0x2a0 [cifs]
> > >> [2158499.701603]  cifs_resolve_server+0x4b/0xd0 [cifs]
> > >> [2158499.701632]  process_one_work+0x1f8/0x3e0
> > >> [2158499.701658]  worker_thread+0x2d/0x3f0
> > >> [2158499.701682]  ? process_one_work+0x3e0/0x3e0
> > >> [2158499.701703]  kthread+0x10d/0x130
> > >> [2158499.701723]  ? kthread_park+0xb0/0xb0
> > >> [2158499.701746]  ret_from_fork+0x1f/0x40
> > >>
> > >> The situation occurs as follows:
> > >> * Some kernel facility invokes dns_query() to resolve a hostname, fo=
r
> > >>   example, "abcdef". The function registers its global DNS resolver
> > >>   cache as current->cred.thread_keyring and passes the query to
> > >>   request_key_net() -> request_key_tag() -> request_key_and_link().
> > >> * Function request_key_and_link() creates a keyring_search_context
> > >>   object. Its match_data.cmp method gets set via a call to
> > >>   type->match_preparse() (resolves to dns_resolver_match_preparse())=
 to
> > >>   dns_resolver_cmp().
> > >> * Function request_key_and_link() continues and invokes
> > >>   search_process_keyrings_rcu() which returns that a given key was n=
ot
> > >>   found. The control is then passed to request_key_and_link() ->
> > >>   construct_alloc_key().
> > >> * Concurrently to that, a second task similarly makes a DNS query fo=
r
> > >>   "abcdef." and its result gets inserted into the DNS resolver cache=
.
> > >> * Back on the first task, function construct_alloc_key() first runs
> > >>   __key_link_begin() to determine an assoc_array_edit operation to
> > >>   insert a new key. Index keys in the array are compared exactly as-=
is,
> > >>   using keyring_compare_object(). The operation finds that "abcdef" =
is
> > >>   not yet present in the destination keyring.
> > >> * Function construct_alloc_key() continues and checks if a given key=
 is
> > >>   already present on some keyring by again calling
> > >>   search_process_keyrings_rcu(). This search is done using
> > >>   dns_resolver_cmp() and "abcdef" gets matched with now present key
> > >>   "abcdef.".
> > >> * The found key is linked on the destination keyring by calling
> > >>   __key_link() and using the previously calculated assoc_array_edit
> > >>   operation. This inserts the "abcdef." key in the array but creates
> > >>   a duplicity because the same index key is already present.
> > >>
> > >> Fix the problem by postponing __key_link_begin() in
> > >> construct_alloc_key() until an actual key which should be linked int=
o
> > >> the destination keyring is determined.
> > >>
> > >> Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
> > >> ---
> > >>  security/keys/request_key.c | 35 ++++++++++++++++++++++++----------=
-
> > >>  1 file changed, 24 insertions(+), 11 deletions(-)
> > >>
> > >> diff --git a/security/keys/request_key.c b/security/keys/request_key=
.c
> > >> index 2da4404276f0..04eb7e4cedad 100644
> > >> --- a/security/keys/request_key.c
> > >> +++ b/security/keys/request_key.c
> > >> @@ -398,17 +398,21 @@ static int construct_alloc_key(struct keyring_=
search_context *ctx,
> > >>  	set_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags);
> > >> =20
> > >>  	if (dest_keyring) {
> > >> -		ret =3D __key_link_lock(dest_keyring, &ctx->index_key);
> > >> +		ret =3D __key_link_lock(dest_keyring, &key->index_key);
> > >>  		if (ret < 0)
> > >>  			goto link_lock_failed;
> > >> -		ret =3D __key_link_begin(dest_keyring, &ctx->index_key, &edit);
> > >> -		if (ret < 0)
> > >> -			goto link_prealloc_failed;
> > >>  	}
> > >> =20
> > >> -	/* attach the key to the destination keyring under lock, but we do=
 need
> > >> +	/*
> > >> +	 * Attach the key to the destination keyring under lock, but we do=
 need
> > >>  	 * to do another check just in case someone beat us to it whilst w=
e
> > >> -	 * waited for locks */
> > >> +	 * waited for locks.
> > >> +	 *
> > >> +	 * The caller might specify a comparison function which looks for =
keys
> > >> +	 * that do not exactly match but are still equivalent from the cal=
ler's
> > >> +	 * perspective. The __key_link_begin() operation must be done only=
 after
> > >> +	 * an actual key is determined.
> > >> +	 */
> > >>  	mutex_lock(&key_construction_mutex);
> > >> =20
> > >>  	rcu_read_lock();
> > >> @@ -417,12 +421,16 @@ static int construct_alloc_key(struct keyring_=
search_context *ctx,
> > >>  	if (!IS_ERR(key_ref))
> > >>  		goto key_already_present;
> > >> =20
> > >> -	if (dest_keyring)
> > >> +	if (dest_keyring) {
> > >> +		ret =3D __key_link_begin(dest_keyring, &key->index_key, &edit);
> > >> +		if (ret < 0)
> > >> +			goto link_alloc_failed;
> > >>  		__key_link(dest_keyring, key, &edit);
> > >> +	}
> > >> =20
> > >>  	mutex_unlock(&key_construction_mutex);
> > >>  	if (dest_keyring)
> > >> -		__key_link_end(dest_keyring, &ctx->index_key, edit);
> > >> +		__key_link_end(dest_keyring, &key->index_key, edit);
> > >>  	mutex_unlock(&user->cons_lock);
> > >>  	*_key =3D key;
> > >>  	kleave(" =3D 0 [%d]", key_serial(key));
> > >> @@ -435,10 +443,13 @@ static int construct_alloc_key(struct keyring_=
search_context *ctx,
> > >>  	mutex_unlock(&key_construction_mutex);
> > >>  	key =3D key_ref_to_ptr(key_ref);
> > >>  	if (dest_keyring) {
> > >> +		ret =3D __key_link_begin(dest_keyring, &key->index_key, &edit);
> > >> +		if (ret < 0)
> > >> +			goto link_alloc_failed_unlocked;
> > >>  		ret =3D __key_link_check_live_key(dest_keyring, key);
> > >>  		if (ret =3D=3D 0)
> > >>  			__key_link(dest_keyring, key, &edit);
> > >> -		__key_link_end(dest_keyring, &ctx->index_key, edit);
> > >> +		__key_link_end(dest_keyring, &key->index_key, edit);
> > >>  		if (ret < 0)
> > >>  			goto link_check_failed;
> > >>  	}
> > >> @@ -453,8 +464,10 @@ static int construct_alloc_key(struct keyring_s=
earch_context *ctx,
> > >>  	kleave(" =3D %d [linkcheck]", ret);
> > >>  	return ret;
> > >> =20
> > >> -link_prealloc_failed:
> > >> -	__key_link_end(dest_keyring, &ctx->index_key, edit);
> > >> +link_alloc_failed:
> > >> +	mutex_unlock(&key_construction_mutex);
> > >> +link_alloc_failed_unlocked:
> > >> +	__key_link_end(dest_keyring, &key->index_key, edit);
> > >>  link_lock_failed:
> > >>  	mutex_unlock(&user->cons_lock);
> > >>  	key_put(key);
> > >> --=20
> > >> 2.35.3
> > >>
> > >=20
> > > A good catch, thanks.
> > >=20
> > > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> >
> > Thank you for the review. Can this be picked through your tree?
> >
> > Cheers,
> > Petr
>
> Hi, I pressed send too early in my respose. I was going to say that
> I'm picking.
>
> I did recently from mutt to aerc, and sometimes get really confused
> what is going on :-)

OK, now it is applied:

https://git.kernel.org/pub/scm/linux/kernel/git/jarkko/linux-tpmdd.git/comm=
it/?id=3D8ea234bb14b53f3bf1ce63dd669d4acbc519ab6d

BR, Jarkko