linux/Documentation/security
David Howells 0837e49ab3 KEYS: Differentiate uses of rcu_dereference_key() and user_key_payload()
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>
2017-03-02 10:09:00 +11:00
..
tpm tpm: move documentation under Documentation/security 2016-11-07 18:56:42 -07:00
00-INDEX ima: new templates management mechanism 2013-10-25 17:17:04 -04:00
IMA-templates.txt ima: added support for new kernel cmdline parameter ima_template_fmt 2014-10-13 08:39:02 -04:00
LSM.txt LSM: Add /sys/kernel/security/lsm 2017-01-19 13:18:29 +11:00
LoadPin.txt LSM: LoadPin for kernel file loading restrictions 2016-04-21 10:47:27 +10:00
SELinux.txt
Smack.txt Smack: limited capability for changing process label 2015-10-19 12:06:47 -07:00
Yama.txt Yama: remove needless CONFIG_SECURITY_YAMA_STACKED 2015-07-28 13:18:19 +10:00
apparmor.txt
conf.py docs: Add more manuals to the PDF build 2016-11-16 16:07:02 -07:00
credentials.txt Documentation: clarify the purpose of LSMs 2011-11-16 12:37:27 +11:00
index.rst tpm: move documentation under Documentation/security 2016-11-07 18:56:42 -07:00
keys-ecryptfs.txt encrypted-keys: move ecryptfs documentation to proper location 2011-06-30 19:08:14 +10:00
keys-request-key.txt
keys-trusted-encrypted.txt Doc: security: keys-trusted: drop duplicate blobauth entry 2016-11-13 22:50:10 -05:00
keys.txt KEYS: Differentiate uses of rcu_dereference_key() and user_key_payload() 2017-03-02 10:09:00 +11:00
self-protection.txt arch: Rename CONFIG_DEBUG_RODATA and CONFIG_DEBUG_MODULE_RONX 2017-02-07 12:32:52 -08:00
tomoyo.txt