fscache_cookie_enabled: check cookie is valid before accessing it

martinetd · martinetd · commit 0dc54bd4d6e0 · 2021-11-03T17:44:29.000+09:00
fscache_cookie_enabled() could be called on NULL cookies and cause a
null pointer dereference when accessing cookie flags: just make sure
the cookie is valid first

Suggested-by: David Howells &lt;dhowells@redhat.com&gt;
Acked-by: David Howells &lt;dhowells@redhat.com&gt;
Signed-off-by: Dominique Martinet &lt;asmadeus@codewreck.org&gt;
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
@@ -167,7 +167,7 @@ struct fscache_cookie {
 
 static inline bool fscache_cookie_enabled(struct fscache_cookie *cookie)
 {
-	return test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
+	return fscache_cookie_valid(cookie) && test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);
 }
 
 /*

Original file line number	Diff line number	Diff line change
`@@ -167,7 +167,7 @@ struct fscache_cookie {`
`167`	`167`
`168`	`168`	`static inline bool fscache_cookie_enabled(struct fscache_cookie *cookie)`
`169`	`169`	`{`
`170`		`- return test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);`
	`170`	`+ return fscache_cookie_valid(cookie) && test_bit(FSCACHE_COOKIE_ENABLED, &cookie->flags);`
`171`	`171`	`}`
`172`	`172`
`173`	`173`	`/*`