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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Eric Biggers <ebiggers@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Jessica Yu <jeyu@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Jeff Vander Stoep <jeffv@google.com>,
        Kees Cook <keescook@chromium.org>,
        Luis Chamberlain <mcgrof@kernel.org>,
        NeilBrown <neilb@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5.4 193/232] fs/filesystems.c: downgrade user-reachable WARN_ONCE() to pr_warn_once()
Date:   Thu, 16 Apr 2020 15:24:47 +0200
Message-Id: <20200416131339.304534097@linuxfoundation.org>
In-Reply-To: <20200416131316.640996080@linuxfoundation.org>
References: <20200416131316.640996080@linuxfoundation.org>
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From: Eric Biggers <ebiggers@google.com>

commit 26c5d78c976ca298e59a56f6101a97b618ba3539 upstream.

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.

Fixes: 41124db869b7 ("fs: warn in case userspace lied about modprobe return")
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jessica Yu <jeyu@kernel.org>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jeff Vander Stoep <jeffv@google.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Luis Chamberlain <mcgrof@kernel.org>
Cc: NeilBrown <neilb@suse.com>
Cc: <stable@vger.kernel.org>		[4.13+]
Link: http://lkml.kernel.org/r/20200312202552.241885-3-ebiggers@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/filesystems.c
+++ b/fs/filesystems.c
@@ -271,7 +271,9 @@ 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)) {