Re: [PATCH 2/3] hfs/hfsplus: initialize data buffer in hfs_bnode_read_u16 and hfs_bnode_read_u8

[Viacheslav Dubeyko <vdubeyko@redhat.com>]

On Fri, 2026-05-01 at 11:02 +0000, Tristan Madani wrote:
> From: Tristan Madani <tristan@talencesecurity.com>
> 
> hfs_bnode_read_u16() and hfs_bnode_read_u8() declare local data buffers
> without initialization, then pass them to hfs_bnode_read().  If
> is_bnode_offset_valid() fails inside hfs_bnode_read(), the function
> returns early without writing to the buffer, leaving it uninitialized.
> The caller then returns the garbage value to its caller.
> 
> This triggers KMSAN uninit-value reports when a corrupted HFS+ image
> has a node_size of 1, causing rec_off to underflow in hfs_bnode_find()
> and the subsequent hfs_bnode_read_u16() to operate on an invalid offset.
> 
> Zero-initialize both buffers so that callers get a deterministic zero
> value when the underlying read fails.
> 
> Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> Tested-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> Fixes: a431930c9bac ("hfs: fix slab-out-of-bounds in hfs_bnode_read()")
> Cc: stable@vger.kernel.org
> Signed-off-by: Tristan Madani <tristan@talencesecurity.com>
> ---
>  fs/hfs/bnode.c     | 4 ++--
>  fs/hfsplus/bnode.c | 4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
> index c00645a4a5733..08307faea7a68 100644
> --- a/fs/hfs/bnode.c
> +++ b/fs/hfs/bnode.c
> @@ -97,7 +97,7 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, u32 off, u32 len)
>  
>  u16 hfs_bnode_read_u16(struct hfs_bnode *node, u32 off)
>  {
> -	__be16 data;
> +	__be16 data = 0;
>  	// optimize later...
>  	hfs_bnode_read(node, &data, off, 2);
>  	return be16_to_cpu(data);
> @@ -105,7 +105,7 @@ u16 hfs_bnode_read_u16(struct hfs_bnode *node, u32 off)
>  
>  u8 hfs_bnode_read_u8(struct hfs_bnode *node, u32 off)
>  {
> -	u8 data;
> +	u8 data = 0;
>  	// optimize later...
>  	hfs_bnode_read(node, &data, off, 1);
>  	return data;
> diff --git a/fs/hfsplus/bnode.c b/fs/hfsplus/bnode.c
> index f8b5a8ae58ff5..35790085b5b2e 100644
> --- a/fs/hfsplus/bnode.c
> +++ b/fs/hfsplus/bnode.c
> @@ -55,7 +55,7 @@ void hfs_bnode_read(struct hfs_bnode *node, void *buf, u32 off, u32 len)
>  
>  u16 hfs_bnode_read_u16(struct hfs_bnode *node, u32 off)
>  {
> -	__be16 data;
> +	__be16 data = 0;
>  	/* TODO: optimize later... */
>  	hfs_bnode_read(node, &data, off, 2);
>  	return be16_to_cpu(data);
> @@ -63,7 +63,7 @@ u16 hfs_bnode_read_u16(struct hfs_bnode *node, u32 off)
>  
>  u8 hfs_bnode_read_u8(struct hfs_bnode *node, u32 off)
>  {
> -	u8 data;
> +	u8 data = 0;
>  	/* TODO: optimize later... */
>  	hfs_bnode_read(node, &data, off, 1);
>  	return data;

If I remember correctly, I already shared that hfs_bnode_read() is called in
multiple places. So, this patch is not enough for complete fix of the issue.

Thanks,
Slava.