Merge branch 'char-misc-next' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/char-misc into fpga-dfl-for-5.4

1 files changed, 19 insertions, 0 deletions

diff --git a/fs/open.c b/fs/open.c
index b5b80469b93d..a59abe3c669a 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -374,6 +374,25 @@ long do_faccessat(int dfd, const char __user *filename, int mode)
 				override_cred->cap_permitted;
 	}
 
+	/*
+	 * The new set of credentials can *only* be used in
+	 * task-synchronous circumstances, and does not need
+	 * RCU freeing, unless somebody then takes a separate
+	 * reference to it.
+	 *
+	 * NOTE! This is _only_ true because this credential
+	 * is used purely for override_creds() that installs
+	 * it as the subjective cred. Other threads will be
+	 * accessing ->real_cred, not the subjective cred.
+	 *
+	 * If somebody _does_ make a copy of this (using the
+	 * 'get_current_cred()' function), that will clear the
+	 * non_rcu field, because now that other user may be
+	 * expecting RCU freeing. But normal thread-synchronous
+	 * cred accesses will keep things non-RCY.
+	 */
+	override_cred->non_rcu = 1;
+
 	old_cred = override_creds(override_cred);
 retry:
 	res = user_path_at(dfd, filename, lookup_flags, &path);