Re: [PATCH] hfsplus: fix uninit-value in hfsplus_strcasecmp

[Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>]

On Tue, 2026-01-20 at 10:41 +0530, Deepanshu Kartikey wrote:
> Syzbot reported a KMSAN uninit-value issue in hfsplus_strcasecmp() during
> filesystem mount operations. The root cause is that hfsplus_find_cat()
> declares a local hfsplus_cat_entry variable without initialization before
> passing it to hfs_brec_read().
> 
> If hfs_brec_read() doesn't completely fill the entire structure (e.g., when
> the on-disk data is shorter than sizeof(hfsplus_cat_entry)), the padding
> bytes in tmp.thread.nodeName remain uninitialized. These uninitialized
> bytes are then copied by hfsplus_cat_build_key_uni() into the search key,
> and subsequently accessed by hfsplus_strcasecmp() during catalog lookups,
> triggering the KMSAN warning.


Frankly speaking, I don't quite follow what is wrong with current logic from
your explanation. Only, struct hfsplus_cat_thread contains nodeName string. And
hfsplus_strcasecmp() can try to compare some strings only for Catalog thread
type. But hfs_brec_read() should read namely only this type of Catalog File
record. So, I cannot imagine how likewise issue could happen. Could you explain
the issue more clearly? How uninitiliazed nodeName strings can be used for
comparison? How does it happened? Because, struct hfsplus_cat_thread is the
biggest item in hfsplus_cat_entry union. The struct hfsplus_cat_file and struct
hfsplus_cat_folder don't contain any strings and strings cannot be used for
comparison in these structures case. But struct hfsplus_cat_thread should be
read completely with the string.

> 
> Fix this by zeroing the tmp variable before use to ensure all padding
> bytes are initialized.
> 
> Reported-by: syzbot+d80abb5b890d39261e72@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=d80abb5b890d39261e72  
> Tested-by: syzbot+d80abb5b890d39261e72@syzkaller.appspotmail.com
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
>  fs/hfsplus/catalog.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
> index 02c1eee4a4b8..9c75d1736427 100644
> --- a/fs/hfsplus/catalog.c
> +++ b/fs/hfsplus/catalog.c
> @@ -199,6 +199,7 @@ int hfsplus_find_cat(struct super_block *sb, u32 cnid,
>  	u16 type;
>  
>  	hfsplus_cat_build_key_with_cnid(sb, fd->search_key, cnid);
> +	memset(&tmp, 0, sizeof(tmp));

What's about of using initialization:

hfsplus_cat_entry tmp = {0};

instead of using memset()?

Thanks,
Slava.

>  	err = hfs_brec_read(fd, &tmp, sizeof(hfsplus_cat_entry));
>  	if (err)
>  		return err;