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KEYS: Differentiate uses of rcu_dereference_key() and user_key_payload()

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rcu_dereference_key() and user_key_payload() are currently being used in
two different, incompatible ways:

 (1) As a wrapper to rcu_dereference() - when only the RCU read lock used
     to protect the key.

 (2) As a wrapper to rcu_dereference_protected() - when the key semaphor is
     used to protect the key and the may be being modified.

Fix this by splitting both of the key wrappers to produce:

 (1) RCU accessors for keys when caller has the key semaphore locked:

	dereference_key_locked()
	user_key_payload_locked()

 (2) RCU accessors for keys when caller holds the RCU read lock:

	dereference_key_rcu()
	user_key_payload_rcu()

This should fix following warning in the NFS idmapper

  ===============================
  [ INFO: suspicious RCU usage. ]
  4.10.0 #1 Tainted: G        W
  -------------------------------
  ./include/keys/user-type.h:53 suspicious rcu_dereference_protected() usage!
  other info that might help us debug this:
  rcu_scheduler_active = 2, debug_locks = 0
  1 lock held by mount.nfs/5987:
    #0:  (rcu_read_lock){......}, at: [<d000000002527abc>] nfs_idmap_get_key+0x15c/0x420 [nfsv4]
  stack backtrace:
  CPU: 1 PID: 5987 Comm: mount.nfs Tainted: G        W       4.10.0 #1
  Call Trace:
    dump_stack+0xe8/0x154 (unreliable)
    lockdep_rcu_suspicious+0x140/0x190
    nfs_idmap_get_key+0x380/0x420 [nfsv4]
    nfs_map_name_to_uid+0x2a0/0x3b0 [nfsv4]
    decode_getfattr_attrs+0xfac/0x16b0 [nfsv4]
    decode_getfattr_generic.constprop.106+0xbc/0x150 [nfsv4]
    nfs4_xdr_dec_lookup_root+0xac/0xb0 [nfsv4]
    rpcauth_unwrap_resp+0xe8/0x140 [sunrpc]
    call_decode+0x29c/0x910 [sunrpc]
    __rpc_execute+0x140/0x8f0 [sunrpc]
    rpc_run_task+0x170/0x200 [sunrpc]
    nfs4_call_sync_sequence+0x68/0xa0 [nfsv4]
    _nfs4_lookup_root.isra.44+0xd0/0xf0 [nfsv4]
    nfs4_lookup_root+0xe0/0x350 [nfsv4]
    nfs4_lookup_root_sec+0x70/0xa0 [nfsv4]
    nfs4_find_root_sec+0xc4/0x100 [nfsv4]
    nfs4_proc_get_rootfh+0x5c/0xf0 [nfsv4]
    nfs4_get_rootfh+0x6c/0x190 [nfsv4]
    nfs4_server_common_setup+0xc4/0x260 [nfsv4]
    nfs4_create_server+0x278/0x3c0 [nfsv4]
    nfs4_remote_mount+0x50/0xb0 [nfsv4]
    mount_fs+0x74/0x210
    vfs_kern_mount+0x78/0x220
    nfs_do_root_mount+0xb0/0x140 [nfsv4]
    nfs4_try_mount+0x60/0x100 [nfsv4]
    nfs_fs_mount+0x5ec/0xda0 [nfs]
    mount_fs+0x74/0x210
    vfs_kern_mount+0x78/0x220
    do_mount+0x254/0xf70
    SyS_mount+0x94/0x100
    system_call+0x38/0xe0

Reported-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Jan Stancek <jstancek@redhat.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>
This commit is contained in:
David Howells
2017-03-01 15:11:23 +00:00
committed by James Morris
parent 6053dc9814
commit 0837e49ab3
15 changed files with 43 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files

2
security/keys/dh.c
View File

@@ -55,7 +55,7 @@ static ssize_t mpi_from_key(key_serial_t keyid, size_t maxlen, MPI *mpi)
if (status == 0) {
const struct user_key_payload *payload;
payload = user_key_payload(key);
payload = user_key_payload_locked(key);
if (maxlen == 0) {
*mpi = NULL;

4
security/keys/encrypted-keys/encrypted.c
View File

@@ -314,7 +314,7 @@ static struct key *request_user_key(const char *master_desc, const u8 **master_k
goto error;
down_read(&ukey->sem);
upayload = user_key_payload(ukey);
upayload = user_key_payload_locked(ukey);
*master_key = upayload->data;
*master_keylen = upayload->datalen;
error:
@@ -926,7 +926,7 @@ static long encrypted_read(const struct key *key, char __user *buffer,
size_t asciiblob_len;
int ret;
epayload = rcu_dereference_key(key);
epayload = dereference_key_locked(key);
/* returns the hex encoded iv, encrypted-data, and hmac as ascii */
asciiblob_len = epayload->datablob_len + ivsize + 1

4
security/keys/trusted.c
View File

@@ -1140,12 +1140,12 @@ out:
static long trusted_read(const struct key *key, char __user *buffer,
size_t buflen)
{
struct trusted_key_payload *p;
const struct trusted_key_payload *p;
char *ascii_buf;
char *bufp;
int i;
p = rcu_dereference_key(key);
p = dereference_key_locked(key);
if (!p)
return -EINVAL;
if (!buffer || buflen <= 0)

6
security/keys/user_defined.c
View File

@@ -107,7 +107,7 @@ int user_update(struct key *key, struct key_preparsed_payload *prep)
/* attach the new data, displacing the old */
key->expiry = prep->expiry;
if (!test_bit(KEY_FLAG_NEGATIVE, &key->flags))
zap = rcu_dereference_key(key);
zap = dereference_key_locked(key);
rcu_assign_keypointer(key, prep->payload.data[0]);
prep->payload.data[0] = NULL;
@@ -123,7 +123,7 @@ EXPORT_SYMBOL_GPL(user_update);
*/
void user_revoke(struct key *key)
{
struct user_key_payload *upayload = key->payload.data[0];
struct user_key_payload *upayload = user_key_payload_locked(key);
/* clear the quota */
key_payload_reserve(key, 0);
@@ -169,7 +169,7 @@ long user_read(const struct key *key, char __user *buffer, size_t buflen)
const struct user_key_payload *upayload;
long ret;
upayload = user_key_payload(key);
upayload = user_key_payload_locked(key);
ret = upayload->datalen;
/* we can return the data as is */