From patchwork Sun Mar 8 17:04:09 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 11425775 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 18137138D for ; Sun, 8 Mar 2020 17:04:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E465120866 for ; Sun, 8 Mar 2020 17:04:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XqcmUVT/" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726451AbgCHREe (ORCPT ); Sun, 8 Mar 2020 13:04:34 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:60017 "EHLO us-smtp-delivery-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726438AbgCHREe (ORCPT ); Sun, 8 Mar 2020 13:04:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583687073; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:in-reply-to:in-reply-to:references:references; bh=SlaPT4r/jCjxOCK3mcnixjvIbrf9quzVkH3kixO1u8A=; b=XqcmUVT/rFzfowZctmlmPUfoFLYMTHwkSf9gpSl0yjtPhv7mYwQDJCn78awUe60IS09Sp2 JKu+UlT/qlTZ8wgR3eiGezQj5gTVB9H0u5vSfGEHIbLsaF6bNQwOVAtaXXa0CTd7uh9zlr p1aoJpCI6FiFSt61Y+5cNiigbMVxFRk= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-227-kphgyoZpN8ypGc-bwg-skw-1; Sun, 08 Mar 2020 13:04:29 -0400 X-MC-Unique: kphgyoZpN8ypGc-bwg-skw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id BCA7D13EA; Sun, 8 Mar 2020 17:04:27 +0000 (UTC) Received: from llong.com (ovpn-120-251.rdu2.redhat.com [10.10.120.251]) by smtp.corp.redhat.com (Postfix) with ESMTP id C8CEF5D9C5; Sun, 8 Mar 2020 17:04:25 +0000 (UTC) From: Waiman Long To: David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Mimi Zohar Cc: keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, Sumit Garg , Jerry Snitselaar , Roberto Sassu , Eric Biggers , Chris von Recklinghausen , Waiman Long Subject: [PATCH v2 1/2] KEYS: Don't write out to userspace while holding key semaphore Date: Sun, 8 Mar 2020 13:04:09 -0400 Message-Id: <20200308170410.14166-2-longman@redhat.com> In-Reply-To: <20200308170410.14166-1-longman@redhat.com> References: <20200308170410.14166-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: 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 the read methods as well as additional changes to not use any userspace write helpers. Signed-off-by: Waiman Long --- include/linux/key-type.h | 2 +- security/keys/big_key.c | 11 +++------ security/keys/encrypted-keys/encrypted.c | 7 +++--- security/keys/keyctl.c | 30 +++++++++++++++++++++-- security/keys/keyring.c | 6 +---- security/keys/request_key_auth.c | 7 +++--- security/keys/trusted-keys/trusted_tpm1.c | 14 ++--------- security/keys/user_defined.c | 5 ++-- 8 files changed, 44 insertions(+), 38 deletions(-) diff --git a/include/linux/key-type.h b/include/linux/key-type.h index 4ded94bcf274..2ab2d6d6aeab 100644 --- a/include/linux/key-type.h +++ b/include/linux/key-type.h @@ -127,7 +127,7 @@ struct key_type { * much is copied into the buffer * - shouldn't do the copy if the buffer is NULL */ - long (*read)(const struct key *key, char __user *buffer, size_t buflen); + long (*read)(const struct key *key, char *buffer, size_t buflen); /* handle request_key() for this type instead of invoking * /sbin/request-key (optional) diff --git a/security/keys/big_key.c b/security/keys/big_key.c index 001abe530a0d..82008f900930 100644 --- a/security/keys/big_key.c +++ b/security/keys/big_key.c @@ -352,7 +352,7 @@ void big_key_describe(const struct key *key, struct seq_file *m) * read the key data * - the key's semaphore is read-locked */ -long big_key_read(const struct key *key, char __user *buffer, size_t buflen) +long big_key_read(const struct key *key, char *buffer, size_t buflen) { size_t datalen = (size_t)key->payload.data[big_key_len]; long ret; @@ -391,9 +391,8 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen) ret = datalen; - /* copy decrypted data to user */ - if (copy_to_user(buffer, buf->virt, datalen) != 0) - ret = -EFAULT; + /* copy out decrypted data */ + memcpy(buffer, buf->virt, datalen); err_fput: fput(file); @@ -401,9 +400,7 @@ long big_key_read(const struct key *key, char __user *buffer, size_t buflen) big_key_free_buffer(buf); } else { ret = datalen; - if (copy_to_user(buffer, key->payload.data[big_key_data], - datalen) != 0) - ret = -EFAULT; + memcpy(buffer, key->payload.data[big_key_data], datalen); } return ret; diff --git a/security/keys/encrypted-keys/encrypted.c b/security/keys/encrypted-keys/encrypted.c index 60720f58cbe0..f6797ba44bf7 100644 --- a/security/keys/encrypted-keys/encrypted.c +++ b/security/keys/encrypted-keys/encrypted.c @@ -902,14 +902,14 @@ static int encrypted_update(struct key *key, struct key_preparsed_payload *prep) } /* - * encrypted_read - format and copy the encrypted data to userspace + * encrypted_read - format and copy out the encrypted data * * The resulting datablob format is: * * * On success, return to userspace the encrypted key datablob size. */ -static long encrypted_read(const struct key *key, char __user *buffer, +static long encrypted_read(const struct key *key, char *buffer, size_t buflen) { struct encrypted_key_payload *epayload; @@ -957,8 +957,7 @@ static long encrypted_read(const struct key *key, char __user *buffer, key_put(mkey); memzero_explicit(derived_key, sizeof(derived_key)); - if (copy_to_user(buffer, ascii_buf, asciiblob_len) != 0) - ret = -EFAULT; + memcpy(buffer, ascii_buf, asciiblob_len); kzfree(ascii_buf); return asciiblob_len; diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 9b898c969558..89a14e71eb0a 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -846,14 +846,40 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) can_read_key: ret = -EOPNOTSUPP; if (key->type->read) { - /* Read the data with the semaphore held (since we might sleep) + /* + * Read the data with the semaphore held (since we might sleep) * to protect against the key being updated or revoked. + * + * Allocating a temporary buffer to hold the keys before + * transferring them to user buffer to avoid potential + * deadlock involving page fault and mmap_sem. */ + char *tmpbuf = NULL; + + if (buffer && buflen) { + tmpbuf = kmalloc(buflen, GFP_KERNEL); + if (!tmpbuf) { + ret = -ENOMEM; + goto error2; + } + } down_read(&key->sem); ret = key_validate(key); if (ret == 0) - ret = key->type->read(key, buffer, buflen); + ret = key->type->read(key, tmpbuf, buflen); up_read(&key->sem); + + /* + * Read methods will just return the required length + * without any copying if the provided length isn't big + * enough. + */ + if ((ret > 0) && (ret <= buflen) && buffer && + copy_to_user(buffer, tmpbuf, ret)) + ret = -EFAULT; + + if (tmpbuf) + kzfree(tmpbuf); } error2: diff --git a/security/keys/keyring.c b/security/keys/keyring.c index febf36c6ddc5..5ca620d31cd3 100644 --- a/security/keys/keyring.c +++ b/security/keys/keyring.c @@ -459,7 +459,6 @@ static int keyring_read_iterator(const void *object, void *data) { struct keyring_read_iterator_context *ctx = data; const struct key *key = keyring_ptr_to_key(object); - int ret; kenter("{%s,%d},,{%zu/%zu}", key->type->name, key->serial, ctx->count, ctx->buflen); @@ -467,10 +466,7 @@ static int keyring_read_iterator(const void *object, void *data) if (ctx->count >= ctx->buflen) return 1; - ret = put_user(key->serial, ctx->buffer); - if (ret < 0) - return ret; - ctx->buffer++; + *ctx->buffer++ = key->serial; ctx->count += sizeof(key->serial); return 0; } diff --git a/security/keys/request_key_auth.c b/security/keys/request_key_auth.c index ecba39c93fd9..41e9735006d0 100644 --- a/security/keys/request_key_auth.c +++ b/security/keys/request_key_auth.c @@ -22,7 +22,7 @@ static int request_key_auth_instantiate(struct key *, static void request_key_auth_describe(const struct key *, struct seq_file *); static void request_key_auth_revoke(struct key *); static void request_key_auth_destroy(struct key *); -static long request_key_auth_read(const struct key *, char __user *, size_t); +static long request_key_auth_read(const struct key *, char *, size_t); /* * The request-key authorisation key type definition. @@ -80,7 +80,7 @@ static void request_key_auth_describe(const struct key *key, * - the key's semaphore is read-locked */ static long request_key_auth_read(const struct key *key, - char __user *buffer, size_t buflen) + char *buffer, size_t buflen) { struct request_key_auth *rka = dereference_key_locked(key); size_t datalen; @@ -97,8 +97,7 @@ static long request_key_auth_read(const struct key *key, if (buflen > datalen) buflen = datalen; - if (copy_to_user(buffer, rka->callout_info, buflen) != 0) - ret = -EFAULT; + memcpy(buffer, rka->callout_info, buflen); } return ret; diff --git a/security/keys/trusted-keys/trusted_tpm1.c b/security/keys/trusted-keys/trusted_tpm1.c index d2c5ec1e040b..8001ab07e63b 100644 --- a/security/keys/trusted-keys/trusted_tpm1.c +++ b/security/keys/trusted-keys/trusted_tpm1.c @@ -1130,11 +1130,10 @@ static int trusted_update(struct key *key, struct key_preparsed_payload *prep) * trusted_read - copy the sealed blob data to userspace in hex. * On success, return to userspace the trusted key datablob size. */ -static long trusted_read(const struct key *key, char __user *buffer, +static long trusted_read(const struct key *key, char *buffer, size_t buflen) { const struct trusted_key_payload *p; - char *ascii_buf; char *bufp; int i; @@ -1143,18 +1142,9 @@ static long trusted_read(const struct key *key, char __user *buffer, return -EINVAL; if (buffer && buflen >= 2 * p->blob_len) { - ascii_buf = kmalloc_array(2, p->blob_len, GFP_KERNEL); - if (!ascii_buf) - return -ENOMEM; - - bufp = ascii_buf; + bufp = buffer; for (i = 0; i < p->blob_len; i++) bufp = hex_byte_pack(bufp, p->blob[i]); - if (copy_to_user(buffer, ascii_buf, 2 * p->blob_len) != 0) { - kzfree(ascii_buf); - return -EFAULT; - } - kzfree(ascii_buf); } return 2 * p->blob_len; } diff --git a/security/keys/user_defined.c b/security/keys/user_defined.c index 6f12de4ce549..07d4287e9084 100644 --- a/security/keys/user_defined.c +++ b/security/keys/user_defined.c @@ -168,7 +168,7 @@ EXPORT_SYMBOL_GPL(user_describe); * read the key data * - the key's semaphore is read-locked */ -long user_read(const struct key *key, char __user *buffer, size_t buflen) +long user_read(const struct key *key, char *buffer, size_t buflen) { const struct user_key_payload *upayload; long ret; @@ -181,8 +181,7 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen) if (buflen > upayload->datalen) buflen = upayload->datalen; - if (copy_to_user(buffer, upayload->data, buflen) != 0) - ret = -EFAULT; + memcpy(buffer, upayload->data, buflen); } return ret; From patchwork Sun Mar 8 17:04:10 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Waiman Long X-Patchwork-Id: 11425779 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D18F1138D for ; Sun, 8 Mar 2020 17:04:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B207320866 for ; Sun, 8 Mar 2020 17:04:48 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="hxM9Rbgp" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726462AbgCHREg (ORCPT ); Sun, 8 Mar 2020 13:04:36 -0400 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:24361 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726449AbgCHREe (ORCPT ); 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Sun, 8 Mar 2020 17:04:27 +0000 (UTC) From: Waiman Long To: David Howells , Jarkko Sakkinen , James Morris , "Serge E. Hallyn" , Mimi Zohar Cc: keyrings@vger.kernel.org, linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org, linux-integrity@vger.kernel.org, Sumit Garg , Jerry Snitselaar , Roberto Sassu , Eric Biggers , Chris von Recklinghausen , Waiman Long Subject: [PATCH v2 2/2] KEYS: Avoid false positive ENOMEM error on key read Date: Sun, 8 Mar 2020 13:04:10 -0400 Message-Id: <20200308170410.14166-3-longman@redhat.com> In-Reply-To: <20200308170410.14166-1-longman@redhat.com> References: <20200308170410.14166-1-longman@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: By allocating a kernel buffer with an user-supplied buffer length, it is possible that a false positive ENOMEM error may be returned because the user-supplied length is just too large even if the system do have enough memory to hold the actual key data. To reduce this possibility, we set a threshold (1024) over which we do check the actual key length first before allocating a buffer of the right size to hold it. Signed-off-by: Waiman Long --- security/keys/keyctl.c | 46 ++++++++++++++++++++++++++++++++---------- 1 file changed, 35 insertions(+), 11 deletions(-) diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c index 89a14e71eb0a..662a638a680d 100644 --- a/security/keys/keyctl.c +++ b/security/keys/keyctl.c @@ -855,28 +855,52 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen) * deadlock involving page fault and mmap_sem. */ char *tmpbuf = NULL; + size_t tbuflen = buflen; - if (buffer && buflen) { - tmpbuf = kmalloc(buflen, GFP_KERNEL); + /* + * We don't want an erronous -ENOMEM error due to an + * arbitrary large user-supplied buflen. So if buflen + * exceeds a threshold (1024 bytes in this case), we call + * the read method twice. The first time to get the buffer + * length and the second time to read out the key data. + * + * N.B. All the read methods will return the required + * buffer length with a NULL input buffer or when + * the input buffer length isn't large enough. + */ + if (buflen && buffer && (buflen <= 0x400)) { +allocbuf: + tmpbuf = kmalloc(tbuflen, GFP_KERNEL); if (!tmpbuf) { ret = -ENOMEM; goto error2; } } + down_read(&key->sem); ret = key_validate(key); if (ret == 0) - ret = key->type->read(key, tmpbuf, buflen); + ret = key->type->read(key, tmpbuf, tbuflen); up_read(&key->sem); - /* - * Read methods will just return the required length - * without any copying if the provided length isn't big - * enough. - */ - if ((ret > 0) && (ret <= buflen) && buffer && - copy_to_user(buffer, tmpbuf, ret)) - ret = -EFAULT; + if ((ret > 0) && (ret <= buflen) && buffer) { + /* + * It is possible, though unlikely, that the key + * changes in between the up_read->down_read period. + * If the key becomes longer, we will have to + * allocate a larger buffer and redo the key read + * again. + */ + if (!tmpbuf || unlikely(ret > tbuflen)) { + tbuflen = ret; + if (unlikely(tmpbuf)) + kzfree(tmpbuf); + goto allocbuf; + } + + if (copy_to_user(buffer, tmpbuf, ret)) + ret = -EFAULT; + } if (tmpbuf) kzfree(tmpbuf);