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SubjectRe: [PATCH] hfs: do not free node before using
On Fri, 2018-11-23 at 17:04 +0800, Pan Bian wrote:
> The function hfs_bmap_free frees node via hfs_bnode_put(node). However,
> it then reads node->this when dumping error message on an error path,
> which may result in a use-after-free bug. This patch frees node only
> when it is never used.
> Fixes: d614267329f("hfs/hfsplus: convert printks to pr_<level>")


While this may indeed be a defect, and the "/* panic */" comment
may be unwarranted, this isn't really a fix of a printk conversion.

This dereference goes back to 2004, the printk(KERN_CRIT to pr_crit(
conversion did not introduce it.

So this patch is only a possible use after free fix.

From a full history git tree:
(similar to

commit a1185ffa2fc491e23f3107a39f66ee703d102153
Author: Andrew Morton <>
Date: Wed Feb 25 16:17:36 2004 -0800

[PATCH] HFS rewrite

From: Roman Zippel <>

This is a complete rewrite of the HFS driver, it gets rid of a all the
special conversion options, which belong in user space. The driver uses now
a btree support very similiar to HFS+, so that both could be merged at some

Thanks to Ethan Benson <> for a number of patches to make
the driver more compliant with the spec and Christoph Hellwig <>
for fixing up the documentation.

> diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
> @@ -338,13 +338,14 @@ void hfs_bmap_free(struct hfs_bnode *node)
> nidx -= len * 8;
> i = node->next;
> - hfs_bnode_put(node);
> if (!i) {
> /* panic */;
> pr_crit("unable to free bnode %u. bmap not found!\n",
> node->this);
> + hfs_bnode_put(node);
> return;
> }
> + hfs_bnode_put(node);
> node = hfs_bnode_find(tree, i);
> if (IS_ERR(node))
> return;

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