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Message-Id: <CT7AR88TXGRA.3BSYSJFL8C5LR@suppilovahvero>
Date: Thu, 08 Jun 2023 16:18:25 +0300
From: "Jarkko Sakkinen" <jarkko@...nel.org>
To: "Petr Pavlu" <petr.pavlu@...e.com>
Cc: <dhowells@...hat.com>, <keyrings@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] keys: Fix linking a duplicate key to a keyring's
assoc_array
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 request
> >> 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 Not 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: 0000000000000005
> >> [2158499.700492] RDX: 0000000000000000 RSI: 0000000000000005 RDI: 0000000000000000
> >> [2158499.700515] RBP: ffffc0bd6187fbb0 R08: ffff9f185faf1100 R09: 0000000000000000
> >> [2158499.700538] R10: ffff9f1ea7da2cc0 R11: 000000005ed8cec8 R12: ffffc0bd6187fc28
> >> [2158499.700561] R13: ffff9f15feb8d000 R14: ffff9f1ea7da2fc0 R15: ffff9f168dc0d740
> >> [2158499.700585] FS: 0000000000000000(0000) GS:ffff9f185fac0000(0000) knlGS:0000000000000000
> >> [2158499.700610] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [2158499.700630] CR2: 00007fdd94fca238 CR3: 0000000809d8c006 CR4: 00000000003706e0
> >> [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, for
> >> 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 not
> >> 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 for
> >> "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 into
> >> the destination keyring is determined.
> >>
> >> Signed-off-by: Petr Pavlu <petr.pavlu@...e.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);
> >>
> >> if (dest_keyring) {
> >> - ret = __key_link_lock(dest_keyring, &ctx->index_key);
> >> + ret = __key_link_lock(dest_keyring, &key->index_key);
> >> if (ret < 0)
> >> goto link_lock_failed;
> >> - ret = __key_link_begin(dest_keyring, &ctx->index_key, &edit);
> >> - if (ret < 0)
> >> - goto link_prealloc_failed;
> >> }
> >>
> >> - /* 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 we
> >> - * 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 caller's
> >> + * perspective. The __key_link_begin() operation must be done only after
> >> + * an actual key is determined.
> >> + */
> >> mutex_lock(&key_construction_mutex);
> >>
> >> 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;
> >>
> >> - if (dest_keyring)
> >> + if (dest_keyring) {
> >> + ret = __key_link_begin(dest_keyring, &key->index_key, &edit);
> >> + if (ret < 0)
> >> + goto link_alloc_failed;
> >> __key_link(dest_keyring, key, &edit);
> >> + }
> >>
> >> 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 = key;
> >> kleave(" = 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 = key_ref_to_ptr(key_ref);
> >> if (dest_keyring) {
> >> + ret = __key_link_begin(dest_keyring, &key->index_key, &edit);
> >> + if (ret < 0)
> >> + goto link_alloc_failed_unlocked;
> >> ret = __key_link_check_live_key(dest_keyring, key);
> >> if (ret == 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_search_context *ctx,
> >> kleave(" = %d [linkcheck]", ret);
> >> return ret;
> >>
> >> -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);
> >> --
> >> 2.35.3
> >>
> >
> > A good catch, thanks.
> >
> > Reviewed-by: Jarkko Sakkinen <jarkko@...nel.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 :-)
BR, Jarkko
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