[syzbot] [hfs?] KMSAN: uninit-value in hfsplus_bnode_find

[syzbot] [hfs?] KMSAN: uninit-value in hfsplus_bnode_find

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    d60bc1401583 Merge tag 'pwrseq-updates-for-v7.1-rc1' of gi..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16cbe8ce580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6b03ae1ea24aea48
dashboard link: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13fe84ce580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11d5feba580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0751271be83e/disk-d60bc140.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/f53e11b04b29/vmlinux-d60bc140.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4c57f9a8e1f1/bzImage-d60bc140.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/438dc293e7d9/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com

loop0: detected capacity change from 0 to 1024
hfsplus: requested invalid offset: NODE: id 0, type 0x1, height 0, node_size 1, offset 4294967295
=====================================================
BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
 hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]
 do_new_mount_fc fs/namespace.c:3763 [inline]
 do_new_mount+0x885/0x1dd0 fs/namespace.c:3839
 path_mount+0x7a2/0x20b0 fs/namespace.c:4159
 do_mount fs/namespace.c:4172 [inline]
 __do_sys_mount fs/namespace.c:4361 [inline]
 __se_sys_mount+0x704/0x7f0 fs/namespace.c:4338
 __x64_sys_mount+0xe4/0x150 fs/namespace.c:4338
 x64_sys_call+0x39f0/0x3ea0 arch/x86/include/generated/asm/syscalls_64.h:166
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x134/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Local variable data.i created at:
 hfsplus_bnode_read_u16 fs/hfsplus/bnode.c:58 [inline]
 hfsplus_bnode_find+0xd6f/0x1600 fs/hfsplus/bnode.c:583
 hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382

CPU: 0 UID: 0 PID: 6044 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
=====================================================


---
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[PATCH] hfsplus: Add a sanity check for catalog btree node size

[Edward Adam Davis]

Syzbot reported a uninit-value bug in [1], during the file system mounting
process, specifically while loading the catalog, a corrupted node_size
value of 1 caused the rec_off argument passed to hfs_bnode_read_u16()
(within hfs_bnode_find()) to be excessively large. Consequently, the
function failed to return a valid value to initialize the off variable,
triggering the bug [1].

To prevent similar issues, a check for the catalog btree node size has
been added within the hfsplus_btree_open() function.

[1]
BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
 hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]

Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 fs/hfsplus/btree.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
index 761c74ccd653..61050ffe425e 100644
--- a/fs/hfsplus/btree.c
+++ b/fs/hfsplus/btree.c
@@ -337,6 +337,11 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
 			pr_err("invalid catalog btree flag\n");
 			goto fail_page;
 		}
+		if (tree->node_size < 2) {
+			pr_err("invalid catalog btree node size %u\n",
+				tree->node_size);
+			goto fail_page;
+		}
 
 		if (test_bit(HFSPLUS_SB_HFSX, &HFSPLUS_SB(sb)->flags) &&
 		    (head->key_type == HFSPLUS_KEY_BINARY))
-- 
2.43.0

Re: [PATCH] hfsplus: Add a sanity check for catalog btree node size

[Viacheslav Dubeyko]

On Wed, 2026-04-15 at 16:29 +0800, Edward Adam Davis wrote:
> Syzbot reported a uninit-value bug in [1], during the file system mounting
> process, specifically while loading the catalog, a corrupted node_size
> value of 1 caused the rec_off argument passed to hfs_bnode_read_u16()
> (within hfs_bnode_find()) to be excessively large. Consequently, the
> function failed to return a valid value to initialize the off variable,
> triggering the bug [1].
> 
> To prevent similar issues, a check for the catalog btree node size has
> been added within the hfsplus_btree_open() function.
> 
> [1]
> BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
>  hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
>  get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
>  get_tree_bdev+0x38/0x50 fs/super.c:1717
>  hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
>  vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
>  fc_mount fs/namespace.c:1193 [inline]
> 
> Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  fs/hfsplus/btree.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> index 761c74ccd653..61050ffe425e 100644
> --- a/fs/hfsplus/btree.c
> +++ b/fs/hfsplus/btree.c
> @@ -337,6 +337,11 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
>  			pr_err("invalid catalog btree flag\n");
>  			goto fail_page;
>  		}
> +		if (tree->node_size < 2) {

Every node starts from BTree node descriptor: struct hfs_bnode_desc. So, the
size of node cannot be lesser than that. However, technical specification
declares that: "The node size (which is expressed in bytes) must be power of
two, from 512 through 32,768, inclusive.". So, we can add more smart check here.

And, maybe, it makes sense to check the node size value at the places of using
it. What do you think?

But we have this check of node_size in hfs_btree_open() [1]:

	size = tree->node_size;
	if (!is_power_of_2(size))
		goto fail_page;

If node size is 1, for example, then this check should fail to execute the
hfs_btree_open(). How, finally, do we have node_size == 1 during the
hfs_bnode_find()? I don't quite follow.

Thanks,
Slava.

> +			pr_err("invalid catalog btree node size %u\n",
> +				tree->node_size);
> +			goto fail_page;
> +		}
>  
>  		if (test_bit(HFSPLUS_SB_HFSX, &HFSPLUS_SB(sb)->flags) &&
>  		    (head->key_type == HFSPLUS_KEY_BINARY))

[1] https://elixir.bootlin.com/linux/v7.0/source/fs/hfsplus/btree.c#L232

Re: [PATCH] hfsplus: Add a sanity check for catalog btree node size

[Edward Adam Davis]

On Wed, 15 Apr 2026 15:32:59 -0700, Viacheslav Dubeyko wrote:
> > Syzbot reported a uninit-value bug in [1], during the file system mounting
> > process, specifically while loading the catalog, a corrupted node_size
> > value of 1 caused the rec_off argument passed to hfs_bnode_read_u16()
> > (within hfs_bnode_find()) to be excessively large. Consequently, the
> > function failed to return a valid value to initialize the off variable,
> > triggering the bug [1].
> >
> > To prevent similar issues, a check for the catalog btree node size has
> > been added within the hfsplus_btree_open() function.
> >
> > [1]
> > BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
> >  hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
> >  hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
> >  hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
> >  get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
> >  get_tree_bdev+0x38/0x50 fs/super.c:1717
> >  hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
> >  vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
> >  fc_mount fs/namespace.c:1193 [inline]
> >
> > Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> > Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> > Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> > ---
> >  fs/hfsplus/btree.c | 5 +++++
> >  1 file changed, 5 insertions(+)
> >
> > diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> > index 761c74ccd653..61050ffe425e 100644
> > --- a/fs/hfsplus/btree.c
> > +++ b/fs/hfsplus/btree.c
> > @@ -337,6 +337,11 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
> >  			pr_err("invalid catalog btree flag\n");
> >  			goto fail_page;
> >  		}
> > +		if (tree->node_size < 2) {
> 
> Every node starts from BTree node descriptor: struct hfs_bnode_desc. So, the
> size of node cannot be lesser than that. However, technical specification
> declares that: "The node size (which is expressed in bytes) must be power of
> two, from 512 through 32,768, inclusive.". So, we can add more smart check here.
Perhaps it could be adjusted as follows:
diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
index 61050ffe425e..287cef5b5c56 100644
--- a/fs/hfsplus/btree.c
+++ b/fs/hfsplus/btree.c
@@ -370,6 +370,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
        }
 
        size = tree->node_size;
+       if (size < sb->s_blocksize || size > HFSPLUS_NODE_MXSZ)
+               goto fail_page;
        if (!is_power_of_2(size))
                goto fail_page;
        if (!tree->node_count)

> 
> And, maybe, it makes sense to check the node size value at the places of using
> it. What do you think?
> 
> But we have this check of node_size in hfs_btree_open() [1]:
> 
> 	size = tree->node_size;
> 	if (!is_power_of_2(size))
> 		goto fail_page;
> 
> If node size is 1, for example, then this check should fail to execute the
> hfs_btree_open(). How, finally, do we have node_size == 1 during the
> hfs_bnode_find()? I don't quite follow.
You overlooked that 2 to the power of 0 is 1.

Edward
BR

[PATCH v2] hfsplus: Add a sanity check for btree node size

[Edward Adam Davis]

Syzbot reported an uninit-value bug in [1] with a corrupted HFS+ image,
during the file system mounting process, specifically while loading the
catalog, a corrupted node_size value of 1 caused the rec_off argument
passed to hfs_bnode_read_u16() (within hfs_bnode_find()) to be excessively
large. Consequently, the function failed to return a valid value to
initialize the off variable, triggering the bug [1].

Every node starts from BTree node descriptor: struct hfs_bnode_desc.
So, the size of node cannot be lesser than that. However, technical
specification declares that: "The node size (which is expressed in bytes)
must be power of two, from 512 through 32,768, inclusive." Add a check
for btree node size base on technical specification.

[1]
BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
 hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]

Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
v1 -> v2: change check base on technical specification

 fs/hfsplus/btree.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
index 761c74ccd653..857705c3fe0d 100644
--- a/fs/hfsplus/btree.c
+++ b/fs/hfsplus/btree.c
@@ -365,6 +365,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
 	}
 
 	size = tree->node_size;
+	if (size < sb->s_blocksize || size > HFSPLUS_NODE_MXSZ)
+		goto fail_page;
 	if (!is_power_of_2(size))
 		goto fail_page;
 	if (!tree->node_count)
-- 
2.43.0

Re: [PATCH v2] hfsplus: Add a sanity check for btree node size

[Viacheslav Dubeyko]

On Thu, 2026-04-16 at 17:53 +0800, Edward Adam Davis wrote:
> Syzbot reported an uninit-value bug in [1] with a corrupted HFS+ image,
> during the file system mounting process, specifically while loading the
> catalog, a corrupted node_size value of 1 caused the rec_off argument
> passed to hfs_bnode_read_u16() (within hfs_bnode_find()) to be excessively
> large. Consequently, the function failed to return a valid value to
> initialize the off variable, triggering the bug [1].
> 
> Every node starts from BTree node descriptor: struct hfs_bnode_desc.
> So, the size of node cannot be lesser than that. However, technical
> specification declares that: "The node size (which is expressed in bytes)
> must be power of two, from 512 through 32,768, inclusive." Add a check
> for btree node size base on technical specification.
> 
> [1]
> BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
>  hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
>  get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
>  get_tree_bdev+0x38/0x50 fs/super.c:1717
>  hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
>  vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
>  fc_mount fs/namespace.c:1193 [inline]
> 
> Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> v1 -> v2: change check base on technical specification
> 
>  fs/hfsplus/btree.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> index 761c74ccd653..857705c3fe0d 100644
> --- a/fs/hfsplus/btree.c
> +++ b/fs/hfsplus/btree.c
> @@ -365,6 +365,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
>  	}
>  
>  	size = tree->node_size;
> +	if (size < sb->s_blocksize || size > HFSPLUS_NODE_MXSZ)

Technically speaking, you are right that b-tree node size should be aligned on
logical block size. However, I am not sure that mkfs.hfsplus restricts the
creation of volume with b-tree's node size smaller than logical block size but
still in the required range of sizes.

Maybe, we need to declare the constant of HFSPLUS_NODE_MINSZ (512) and to check
this constant instead of logical block size. What do you think?

Thanks,
Slava. 

> +		goto fail_page;
>  	if (!is_power_of_2(size))
>  		goto fail_page;
>  	if (!tree->node_count)

Re: [PATCH v2] hfsplus: Add a sanity check for btree node size

[Edward Adam Davis]

On Thu, 16 Apr 2026 15:16:15 -0700, Viacheslav Dubeyko wrote:
> > Syzbot reported an uninit-value bug in [1] with a corrupted HFS+ image,
> > during the file system mounting process, specifically while loading the
> > catalog, a corrupted node_size value of 1 caused the rec_off argument
> > passed to hfs_bnode_read_u16() (within hfs_bnode_find()) to be excessively
> > large. Consequently, the function failed to return a valid value to
> > initialize the off variable, triggering the bug [1].
> > 
> > Every node starts from BTree node descriptor: struct hfs_bnode_desc.
> > So, the size of node cannot be lesser than that. However, technical
> > specification declares that: "The node size (which is expressed in bytes)
> > must be power of two, from 512 through 32,768, inclusive." Add a check
> > for btree node size base on technical specification.
> > 
> > [1]
> > BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
> >  hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
> >  hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
> >  hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
> >  get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
> >  get_tree_bdev+0x38/0x50 fs/super.c:1717
> >  hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
> >  vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
> >  fc_mount fs/namespace.c:1193 [inline]
> > 
> > Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> > Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> > Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> > ---
> > v1 -> v2: change check base on technical specification
> > 
> >  fs/hfsplus/btree.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> > index 761c74ccd653..857705c3fe0d 100644
> > --- a/fs/hfsplus/btree.c
> > +++ b/fs/hfsplus/btree.c
> > @@ -365,6 +365,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
> >  	}
> >  
> >  	size = tree->node_size;
> > +	if (size < sb->s_blocksize || size > HFSPLUS_NODE_MXSZ)
> 
> Technically speaking, you are right that b-tree node size should be aligned on
> logical block size. However, I am not sure that mkfs.hfsplus restricts the
> creation of volume with b-tree's node size smaller than logical block size but
> still in the required range of sizes.
> 
> Maybe, we need to declare the constant of HFSPLUS_NODE_MINSZ (512) and to check
> this constant instead of logical block size. What do you think?
Hmm, that's much safer.

Edward
BR

[PATCH v3] hfsplus: Add a sanity check for btree node size

[Edward Adam Davis]

Syzbot reported an uninit-value bug in [1] with a corrupted HFS+ image,
during the file system mounting process, specifically while loading the
catalog, a corrupted node_size value of 1 caused the rec_off argument
passed to hfs_bnode_read_u16() (within hfs_bnode_find()) to be excessively
large. Consequently, the function failed to return a valid value to
initialize the off variable, triggering the bug [1].

Every node starts from BTree node descriptor: struct hfs_bnode_desc.
So, the size of node cannot be lesser than that. However, technical
specification declares that: "The node size (which is expressed in bytes)
must be power of two, from 512 through 32,768, inclusive." Add a check
for btree node size base on technical specification.

[1]
BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
 hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
 hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
 get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
 get_tree_bdev+0x38/0x50 fs/super.c:1717
 hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
 vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
 fc_mount fs/namespace.c:1193 [inline]

Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
v1 -> v2: change check base on technical specification
v2 -> v3: using const min size

 fs/hfsplus/btree.c         | 2 ++
 include/linux/hfs_common.h | 1 +
 2 files changed, 3 insertions(+)

diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
index 761c74ccd653..394542a47e60 100644
--- a/fs/hfsplus/btree.c
+++ b/fs/hfsplus/btree.c
@@ -365,6 +365,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
 	}
 
 	size = tree->node_size;
+	if (size < HFSPLUS_NODE_MINSZ || size > HFSPLUS_NODE_MXSZ)
+		goto fail_page;
 	if (!is_power_of_2(size))
 		goto fail_page;
 	if (!tree->node_count)
diff --git a/include/linux/hfs_common.h b/include/linux/hfs_common.h
index 07dfc39630ab..45fb4c9ff9f5 100644
--- a/include/linux/hfs_common.h
+++ b/include/linux/hfs_common.h
@@ -513,6 +513,7 @@ struct hfs_btree_header_rec {
 /* HFS+ BTree misc info */
 #define HFSPLUS_TREE_HEAD			0
 #define HFSPLUS_NODE_MXSZ			32768
+#define HFSPLUS_NODE_MINSZ			512
 #define HFSPLUS_ATTR_TREE_NODE_SIZE		8192
 #define HFSPLUS_BTREE_HDR_NODE_RECS_COUNT	3
 #define HFSPLUS_BTREE_HDR_MAP_REC_INDEX		2	/* Map (bitmap) record in Header node */
-- 
2.43.0

Re: [PATCH v3] hfsplus: Add a sanity check for btree node size

[Viacheslav Dubeyko]

On Fri, 2026-04-17 at 07:44 +0800, Edward Adam Davis wrote:
> Syzbot reported an uninit-value bug in [1] with a corrupted HFS+ image,
> during the file system mounting process, specifically while loading the
> catalog, a corrupted node_size value of 1 caused the rec_off argument
> passed to hfs_bnode_read_u16() (within hfs_bnode_find()) to be excessively
> large. Consequently, the function failed to return a valid value to
> initialize the off variable, triggering the bug [1].
> 
> Every node starts from BTree node descriptor: struct hfs_bnode_desc.
> So, the size of node cannot be lesser than that. However, technical
> specification declares that: "The node size (which is expressed in bytes)
> must be power of two, from 512 through 32,768, inclusive." Add a check
> for btree node size base on technical specification.
> 
> [1]
> BUG: KMSAN: uninit-value in hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_bnode_find+0x141c/0x1600 fs/hfsplus/bnode.c:584
>  hfsplus_btree_open+0x169a/0x1e40 fs/hfsplus/btree.c:382
>  hfsplus_fill_super+0x111f/0x2770 fs/hfsplus/super.c:553
>  get_tree_bdev_flags+0x6e6/0x920 fs/super.c:1694
>  get_tree_bdev+0x38/0x50 fs/super.c:1717
>  hfsplus_get_tree+0x35/0x40 fs/hfsplus/super.c:709
>  vfs_get_tree+0xb3/0x5d0 fs/super.c:1754
>  fc_mount fs/namespace.c:1193 [inline]
> 
> Fixes: 8ad2c6a36ac4 ("hfsplus: validate b-tree node 0 bitmap at mount time")
> Reported-by: syzbot+217eb327242d08197efb@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=217eb327242d08197efb
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
> v1 -> v2: change check base on technical specification
> v2 -> v3: using const min size
> 
>  fs/hfsplus/btree.c         | 2 ++
>  include/linux/hfs_common.h | 1 +
>  2 files changed, 3 insertions(+)
> 
> diff --git a/fs/hfsplus/btree.c b/fs/hfsplus/btree.c
> index 761c74ccd653..394542a47e60 100644
> --- a/fs/hfsplus/btree.c
> +++ b/fs/hfsplus/btree.c
> @@ -365,6 +365,8 @@ struct hfs_btree *hfs_btree_open(struct super_block *sb, u32 id)
>  	}
>  
>  	size = tree->node_size;
> +	if (size < HFSPLUS_NODE_MINSZ || size > HFSPLUS_NODE_MXSZ)
> +		goto fail_page;
>  	if (!is_power_of_2(size))
>  		goto fail_page;
>  	if (!tree->node_count)
> diff --git a/include/linux/hfs_common.h b/include/linux/hfs_common.h
> index 07dfc39630ab..45fb4c9ff9f5 100644
> --- a/include/linux/hfs_common.h
> +++ b/include/linux/hfs_common.h
> @@ -513,6 +513,7 @@ struct hfs_btree_header_rec {
>  /* HFS+ BTree misc info */
>  #define HFSPLUS_TREE_HEAD			0
>  #define HFSPLUS_NODE_MXSZ			32768
> +#define HFSPLUS_NODE_MINSZ			512
>  #define HFSPLUS_ATTR_TREE_NODE_SIZE		8192
>  #define HFSPLUS_BTREE_HDR_NODE_RECS_COUNT	3
>  #define HFSPLUS_BTREE_HDR_MAP_REC_INDEX		2	/* Map (bitmap) record in Header node */

Looks good. Thanks a lot for the fix.

Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>

Thanks,
Slava.