linux-kernel - [PATCH 2/6] vfs: Fix fs_context logging when there's no log

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Message-ID: <153484531201.1183.24087901695718354.stgit@warthog.procyon.org.uk>
Date:   Tue, 21 Aug 2018 10:55:12 +0100
From:   David Howells <dhowells@...hat.com>
To:     viro@...iv.linux.org.uk
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/6] vfs: Fix fs_context logging when there's no log

If an fs_context-based mount is called from mount(2) or some other place
that doesn't set up the logging-through-fd, then under some circumstances
an oops will occur due to the log being unconditionally accessed in
logfc().

Fix this by checking whether there is a log structure before attempting to
access it

Fixes: 06b830edff9f ("vfs: Implement logging through fs_context")
Signed-off-by: David Howells <dhowells@...hat.com>
---

 fs/fs_context.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/fs_context.c b/fs/fs_context.c
index 14921b2c1e42..053b8d0f11ea 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -416,7 +416,7 @@ void logfc(struct fs_context *fc, const char *fmt, ...)
 	if ((unsigned long)p >= (unsigned long)__start_rodata &&
 	    (unsigned long)p <  (unsigned long)__end_rodata)
 		goto const_string;
-	if (within_module_core((unsigned long)p, log->owner))
+	if (log && within_module_core((unsigned long)p, log->owner))
 		goto const_string;
 	q = kstrdup(p, GFP_KERNEL);
 	goto copied_string;