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

From: David Howells
Date: Tue Aug 21 2018 - 05:55:16 EST

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

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@xxxxxxxxxx>

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;