Re: Forwarded: Re: [syzbot] [hfs?] KASAN: slab-out-of-bounds Read in hfsplus_bnode_read

[Hillf Danton]

> Date: Thu, 30 Apr 2026 15:41:35 -0700	[thread overview]
> For archival purposes, forwarding an incoming command email to
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> ***
> 
> Subject: Re: [syzbot] [hfs?] KASAN: slab-out-of-bounds Read in hfsplus_bnode_read
> Author: tristmd@xxxxxxxxx
> 
Tristan, can you please correctly fill your cc list as required to avoid this
Forwarded message which is a waste of net bandwidth?

> #syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 
> >From 481707e6b354ae2f36603d68c63364b56d6ee6b6 Mon Sep 17 00:00:00 2001
> From: Tristan Madani <tristan@xxxxxxxxxxxxxxxxxxx>
> Date: Thu, 30 Apr 2026 22:38:32 +0000
> Subject: [PATCH 1/3] hfs/hfsplus: fix u32 overflow in
>  check_and_correct_requested_length
> 
> check_and_correct_requested_length() compares (off + len) against
> node_size using u32 arithmetic.  When the caller passes a large len
> value (e.g. from an underflowed subtraction in hfs_brec_remove()),
> off + len can wrap past 2^32 and produce a small result, causing the
> bounds check to pass when it should fail.
> 
> For example, with off=14 and len=0xFFFFFFF2 (underflowed from
> data_off - keyoffset - size in hfs_brec_remove), off + len wraps to 6,
> which is less than a typical node_size of 512, so the check passes and
> the subsequent memmove reads ~4GB past the node buffer.
> 
> Fix this by comparing len against (node_size - off) instead.  Since
> is_bnode_offset_valid() already guarantees off < node_size before this
> point, the subtraction cannot underflow.
> 
> Reported-by: syzbot+6df204b70bf3261691c5@xxxxxxxxxxxxxxxxxxxxxxxxx
> Reported-by: syzbot+e76bf3d19b85350571ac@xxxxxxxxxxxxxxxxxxxxxxxxx
> Fixes: a431930c9bac ("hfs: fix slab-out-of-bounds in hfs_bnode_read()")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Tristan Madani <tristan@xxxxxxxxxxxxxxxxxxx>
> ---
>  fs/hfs/bnode.c          | 2 +-
>  fs/hfsplus/hfsplus_fs.h | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/hfs/bnode.c b/fs/hfs/bnode.c
> index 13d58c51fc46b..c00645a4a5733 100644
> --- a/fs/hfs/bnode.c
> +++ b/fs/hfs/bnode.c
> @@ -41,7 +41,7 @@ u32 check_and_correct_requested_length(struct hfs_bnode *node, u32 off, u32 len)
>  
>  	node_size = node->tree->node_size;
>  
> -	if ((off + len) > node_size) {
> +	if (len > node_size - off) {
>  		u32 new_len = node_size - off;
>  
>  		pr_err("requested length has been corrected: "
> diff --git a/fs/hfsplus/hfsplus_fs.h b/fs/hfsplus/hfsplus_fs.h
> index 3545b8dbf11c5..10b2dda3f8044 100644
> --- a/fs/hfsplus/hfsplus_fs.h
> +++ b/fs/hfsplus/hfsplus_fs.h
> @@ -600,7 +600,7 @@ u32 check_and_correct_requested_length(struct hfs_bnode *node, u32 off, u32 len)
>  
>  	node_size = node->tree->node_size;
>  
> -	if ((off + len) > node_size) {
> +	if (len > node_size - off) {
>  		u32 new_len = node_size - off;
>  
>  		pr_err("requested length has been corrected: "
> -- 
> 2.47.3