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/20211025192746.66445-26-krisman@collabora.com
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index cedcb15..45df610 100644 (file)
--- 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;
 }
 
 /*