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.

Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
 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;
-- 
2.47.0

On Tue, Nov 05, 2024 at 12:42:14AM +0100, Thorsten Blum wrote:
> 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.

This is two different things, why not do this in two different patches?

thanks,

greg k-h

On 5. Nov 2024, at 10:52, Greg KH wrote:
> On Tue, Nov 05, 2024 at 12:42:14AM +0100, Thorsten Blum wrote:
>> 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.
> 
> This is two different things, why not do this in two different patches?
> 
> thanks,
> 
> greg k-h

No particular reason. I'll submit a v2 for the __counted_by() annotation
and a separate patch for struct_size().

I'll keep Jan's Reviewed-by: tag for both.

Thanks,
Thorsten