Merge tag 'keys-request-20190626' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull request_key improvements from David Howells:
 "These are all request_key()-related, including a fix and some improvements:

   - Fix the lack of a Link permission check on a key found by
     request_key(), thereby enabling request_key() to link keys that
     don't grant this permission to the target keyring (which must still
     grant Write permission).

     Note that the key must be in the caller's keyrings already to be
     found.

   - Invalidate used request_key authentication keys rather than
     revoking them, so that they get cleaned up immediately rather than
     hanging around till the expiry time is passed.

   - Move the RCU locks outwards from the keyring search functions so
     that a request_key_rcu() can be provided. This can be called in RCU
     mode, so it can't sleep and can't upcall - but it can be called
     from LOOKUP_RCU pathwalk mode.

   - Cache the latest positive result of request_key*() temporarily in
     task_struct so that filesystems that make a lot of request_key()
     calls during pathwalk can take advantage of it to avoid having to
     redo the searching. This requires CONFIG_KEYS_REQUEST_CACHE=y.

     It is assumed that the key just found is likely to be used multiple
     times in each step in an RCU pathwalk, and is likely to be reused
     for the next step too.

     Note that the cleanup of the cache is done on TIF_NOTIFY_RESUME,
     just before userspace resumes, and on exit"

* tag 'keys-request-20190626' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
  keys: Kill off request_key_async{,_with_auxdata}
  keys: Cache result of request_key*() temporarily in task_struct
  keys: Provide request_key_rcu()
  keys: Move the RCU locks outwards from the keyring search functions
  keys: Invalidate used request_key authentication keys
  keys: Fix request_key() lack of Link perm check on found key

1 files changed, 18 insertions, 0 deletions

diff --git a/security/keys/Kconfig b/security/keys/Kconfig
index ee502e4d390b..dd313438fecf 100644
--- a/security/keys/Kconfig
+++ b/security/keys/Kconfig
@@ -25,6 +25,24 @@ config KEYS_COMPAT
 	def_bool y
 	depends on COMPAT && KEYS
 
+config KEYS_REQUEST_CACHE
+	bool "Enable temporary caching of the last request_key() result"
+	depends on KEYS
+	help
+	  This option causes the result of the last successful request_key()
+	  call that didn't upcall to the kernel to be cached temporarily in the
+	  task_struct.  The cache is cleared by exit and just prior to the
+	  resumption of userspace.
+
+	  This allows the key used for multiple step processes where each step
+	  wants to request a key that is likely the same as the one requested
+	  by the last step to save on the searching.
+
+	  An example of such a process is a pathwalk through a network
+	  filesystem in which each method needs to request an authentication
+	  key.  Pathwalk will call multiple methods for each dentry traversed
+	  (permission, d_revalidate, lookup, getxattr, getacl, ...).
+
 config PERSISTENT_KEYRINGS
 	bool "Enable register of persistent per-UID keyrings"
 	depends on KEYS