[PATCH] fanotify: prove that structure size is correct

[Kees Cook]

When building with CONFIG_DEBUG_STRICT_USER_COPY_CHECKS, this copy_to_user
wasn't provably correct (the length was in a variable but the structure
wasn't). The compiler wasn't able to check that the length was being
statically assigned, so include a BUG_ON to notice if this ever changes.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/notify/fanotify/fanotify_user.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index b13992a41bd9..7bdb43222875 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -216,6 +216,7 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
 
 	fd = fanotify_event_metadata.fd;
 	ret = -EFAULT;
+	BUG_ON(fanotify_event_metadata.event_len != FAN_EVENT_METADATA_LEN);
 	if (copy_to_user(buf, &fanotify_event_metadata,
 			 fanotify_event_metadata.event_len))
 		goto out_close_fd;
-- 
1.9.1


-- 
Kees Cook
Chrome OS Security
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