linux-ext4 - [PATCH v8 26/32] fanotify: WARN_ON against too large file handles

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Message-Id: <20211019000015.1666608-27-krisman@collabora.com>
Date:   Mon, 18 Oct 2021 21:00:09 -0300
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     jack@...e.com, amir73il@...il.com
Cc:     djwong@...nel.org, tytso@....edu, david@...morbit.com,
        dhowells@...hat.com, khazhy@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-api@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com
Subject: [PATCH v8 26/32] 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.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
---
 fs/notify/fanotify/fanotify.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index cedcb1546804..45df610debbe 100644
--- 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;
 }
 
 /*
-- 
2.33.0