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().

When the filesystem image is corrupted or malformed (as syzbot fuzzes),
hfs_brec_read() may read less data than sizeof(hfsplus_cat_entry). In such
cases, the tmp.thread.nodeName.unicode array may only be partially filled,
leaving remaining bytes uninitialized.

hfsplus_cat_build_key_uni() then copies from this array based on
nodeName.length. If the on-disk length field is corrupted or the array
wasn't fully written by hfs_brec_read(), uninitialized stack data gets
copied into the search key. When hfsplus_strcasecmp() subsequently reads
these uninitialized bytes and uses them in case_fold() as an array index
into hfsplus_case_fold_table, KMSAN detects the use of uninitialized values.

Fix this by initializing tmp to zero, ensuring that even with corrupted
filesystem images, no uninitialized data is propagated.

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")
Link: https://lore.kernel.org/all/20260120051114.1281285-1-kartikey406@gmail.com/T/ [v1]
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
Changes in v2:
- Use structure initialization (= {0}) instead of memset() as suggested
  by Viacheslav Dubeyko
- Improved commit message to clarify how uninitialized data is used
---
 fs/hfsplus/catalog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
index 02c1eee4a4b8..56a53d2d437e 100644
--- a/fs/hfsplus/catalog.c
+++ b/fs/hfsplus/catalog.c
@@ -194,7 +194,7 @@ static int hfsplus_fill_cat_thread(struct super_block *sb,
 int hfsplus_find_cat(struct super_block *sb, u32 cnid,
 		     struct hfs_find_data *fd)
 {
-	hfsplus_cat_entry tmp;
+	hfsplus_cat_entry tmp = {0};
 	int err;
 	u16 type;
 
-- 
2.43.0

On Wed, 2026-01-21 at 12:01 +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().
> 
> When the filesystem image is corrupted or malformed (as syzbot fuzzes),
> hfs_brec_read() may read less data than sizeof(hfsplus_cat_entry). In such
> cases, the tmp.thread.nodeName.unicode array may only be partially filled,
> leaving remaining bytes uninitialized.

I still don't understand this point. Please, see my questions in the thread for
v1 of the patch. Could you please address my questions/worries?

Thanks,
Slava.

> 
> hfsplus_cat_build_key_uni() then copies from this array based on
> nodeName.length. If the on-disk length field is corrupted or the array
> wasn't fully written by hfs_brec_read(), uninitialized stack data gets
> copied into the search key. When hfsplus_strcasecmp() subsequently reads
> these uninitialized bytes and uses them in case_fold() as an array index
> into hfsplus_case_fold_table, KMSAN detects the use of uninitialized values.
> 
> Fix this by initializing tmp to zero, ensuring that even with corrupted
> filesystem images, no uninitialized data is propagated.
> 
> 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")
> Link: https://lore.kernel.org/all/20260120051114.1281285-1-kartikey406@gmail.com/T/   [v1]
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
> Changes in v2:
> - Use structure initialization (= {0}) instead of memset() as suggested
>   by Viacheslav Dubeyko
> - Improved commit message to clarify how uninitialized data is used
> ---
>  fs/hfsplus/catalog.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/hfsplus/catalog.c b/fs/hfsplus/catalog.c
> index 02c1eee4a4b8..56a53d2d437e 100644
> --- a/fs/hfsplus/catalog.c
> +++ b/fs/hfsplus/catalog.c
> @@ -194,7 +194,7 @@ static int hfsplus_fill_cat_thread(struct super_block *sb,
>  int hfsplus_find_cat(struct super_block *sb, u32 cnid,
>  		     struct hfs_find_data *fd)
>  {
> -	hfsplus_cat_entry tmp;
> +	hfsplus_cat_entry tmp = {0};
>  	int err;
>  	u16 type;
>