linux-hardening - [RESEND PATCH] ext4: Annotate struct fname with __counted

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Message-ID: <20241007130716.3442-1-thorsten.blum@toblux.com>
Date: Mon,  7 Oct 2024 15:07:16 +0200
From: Thorsten Blum <thorsten.blum@...lux.com>
To: "Theodore Ts'o" <tytso@....edu>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Thorsten Blum <thorsten.blum@...lux.com>,
	Jan Kara <jack@...e.cz>,
	linux-ext4@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: [RESEND PATCH] ext4: Annotate struct fname with __counted_by()

Add the __counted_by compiler attribute to the flexible array member
name to improve access bounds-checking via CONFIG_UBSAN_BOUNDS and
CONFIG_FORTIFY_SOURCE.

Inline and use struct_size() to calculate the number of bytes to
allocate for new_fn and remove the local variable len.

Signed-off-by: Thorsten Blum <thorsten.blum@...lux.com>
Reviewed-by: Jan Kara <jack@...e.cz>
---
 fs/ext4/dir.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/dir.c b/fs/ext4/dir.c
index ef6a3c8f3a9a..02d47a64e8d1 100644
--- a/fs/ext4/dir.c
+++ b/fs/ext4/dir.c
@@ -418,7 +418,7 @@ struct fname {
 	__u32		inode;
 	__u8		name_len;
 	__u8		file_type;
-	char		name[];
+	char		name[] __counted_by(name_len);
 };
 
 /*
@@ -471,14 +471,13 @@ int ext4_htree_store_dirent(struct file *dir_file, __u32 hash,
 	struct rb_node **p, *parent = NULL;
 	struct fname *fname, *new_fn;
 	struct dir_private_info *info;
-	int len;
 
 	info = dir_file->private_data;
 	p = &info->root.rb_node;
 
 	/* Create and allocate the fname structure */
-	len = sizeof(struct fname) + ent_name->len + 1;
-	new_fn = kzalloc(len, GFP_KERNEL);
+	new_fn = kzalloc(struct_size(new_fn, name, ent_name->len + 1),
+			 GFP_KERNEL);
 	if (!new_fn)
 		return -ENOMEM;
 	new_fn->hash = hash;
-- 
2.46.2