fanotify: WARN_ON against too large file handles

struct fanotify_error_event, at least, is preallocated and isn't able to to handle arbitrarily large file handles. Future-proof the code by complaining loudly if a handle larger than MAX_HANDLE_SZ is ever found. Link: https://lore.kernel.org/r/[email protected] Reviewed-by: Amir Goldstein <[email protected]> Reviewed-by: Jan Kara <[email protected]> Signed-off-by: Gabriel Krisman Bertazi <[email protected]> Signed-off-by: Jan Kara <[email protected]>
noroot · Oct 27, 2021 · 572c28f · 572c28f
1 parent 4bd5a5c
commit 572c28f
Showing 1 changed file with 11 additions and 1 deletion.
diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
@@ -360,13 +360,23 @@ static u32 fanotify_group_event_mask(struct fsnotify_group *group,
 static int fanotify_encode_fh_len(struct inode *inode)
 {
 	int dwords = 0;
+	int fh_len;
 
 	if (!inode)
 		return 0;
 
 	exportfs_encode_inode_fh(inode, NULL, &dwords, NULL);
+	fh_len = dwords << 2;
 
-	return dwords << 2;
+	/*
+	 * struct fanotify_error_event might be preallocated and is
+	 * limited to MAX_HANDLE_SZ.  This should never happen, but
+	 * safeguard by forcing an invalid file handle.
+	 */
+	if (WARN_ON_ONCE(fh_len > MAX_HANDLE_SZ))
+		return 0;
+
+	return fh_len;
 }
 
 /*