[PATCH v3 1/3] KEYS: Don't write out to userspace while holding key semaphore

From: Waiman Long
Date: Fri Mar 13 2020 - 11:21:36 EST

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 <longman@xxxxxxxxxx>
---
include/linux/key-type.h | 2 +-
security/keys/big_key.c | 11 ++---
security/keys/encrypted-keys/encrypted.c | 7 ++-
security/keys/keyctl.c | 57 +++++++++++++++++++----
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, 65 insertions(+), 44 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:
* <master-key name> <decrypted data length> <encrypted iv> <encrypted data>
*
* 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..81f68e434b9f 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -797,6 +797,21 @@ long keyctl_keyring_search(key_serial_t ringid,
return ret;
}

+/*
+ * Call the read method
+ */
+static long __keyctl_read_key(struct key *key, char *buffer, size_t buflen)
+{
+ long ret;
+
+ down_read(&key->sem);
+ ret = key_validate(key);
+ if (ret == 0)
+ ret = key->type->read(key, buffer, buflen);
+ up_read(&key->sem);
+ return ret;
+}
+
/*
* Read a key's payload.
*
@@ -844,16 +859,42 @@ long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)

/* the key is probably readable - now try to read it */
can_read_key:
- ret = -EOPNOTSUPP;
- if (key->type->read) {
- /* Read the data with the semaphore held (since we might sleep)
+ if (!key->type->read) {
+ ret = -EOPNOTSUPP;
+ goto error2;
+ }
+
+ if (!buffer || !buflen) {
+ /* Get the key length from the read method */
+ ret = __keyctl_read_key(key, NULL, 0);
+ } else {
+
+ /*
+ * 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 = kmalloc(buflen, GFP_KERNEL);
+
+ if (!tmpbuf) {
+ ret = -ENOMEM;
+ goto error2;
+ }
+ ret = __keyctl_read_key(key, tmpbuf, buflen);
+
+ /*
+ * Read methods will just return the required length
+ * without any copying if the provided length isn't big
+ * enough.
*/
- down_read(&key->sem);
- ret = key_validate(key);
- if (ret == 0)
- ret = key->type->read(key, buffer, buflen);
- up_read(&key->sem);
+ if ((ret > 0) && (ret <= buflen)) {
+ if (copy_to_user(buffer, tmpbuf, ret))
+ ret = -EFAULT;
+ }
+ 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;
--
2.18.1