[27/35] fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()

Commit Message

Andrew Morton April 10, 2020, 9:33 p.m. UTC

From: Eric Biggers <[e-mail]>
Subject: fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()

After request_module(), nothing is stopping the module from being unloaded
until someone takes a reference to it via try_get_module().

The WARN_ONCE() in get_fs_type() is thus user-reachable, via userspace
running 'rmmod' concurrently.

Since WARN_ONCE() is for kernel bugs only, not for user-reachable
situations, downgrade this warning to pr_warn_once().

Keep it printed once only, since the intent of this warning is to detect a
bug in modprobe at boot time.  Printing the warning more than once
wouldn't really provide any useful extra information.

Link: http://lkml.kernel.org/r/[e-mail]
Fixes: 41124db869b7 ("fs: warn in case userspace lied about modprobe return")
Signed-off-by: Eric Biggers <[e-mail]>
Reviewed-by: Jessica Yu <[e-mail]>
Cc: Alexei Starovoitov <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Cc: Jeff Vander Stoep <[e-mail]>
Cc: Jessica Yu <[e-mail]>
Cc: Kees Cook <[e-mail]>
Cc: Luis Chamberlain <[e-mail]>
Cc: NeilBrown <[e-mail]>
Cc: <[e-mail]>		[4.13+]
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/filesystems.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Patch

--- a/fs/filesystems.c~fs-filesystemsc-downgrade-user-reachable-warn_once-to-pr_warn_once
+++ a/fs/filesystems.c
@@ -272,7 +272,9 @@  struct file_system_type *get_fs_type(con
 	fs = __get_fs_type(name, len);
 	if (!fs && (request_module("fs-%.*s", len, name) == 0)) {
 		fs = __get_fs_type(name, len);
-		WARN_ONCE(!fs, "request_module fs-%.*s succeeded, but still no fs?\n", len, name);
+		if (!fs)
+			pr_warn_once("request_module fs-%.*s succeeded, but still no fs?\n",
+				     len, name);
 	}
 
 	if (dot && fs && !(fs->fs_flags & FS_HAS_SUBTYPE)) {