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>")
Signed-off-by: Pan Bian <[email protected]>
---
fs/hfs/btree.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
index 98b96ff..19017d2 100644
--- 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;
--
2.7.4
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>")
Hi.
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 https://archive.org/details/git-history-of-linux)
commit a1185ffa2fc491e23f3107a39f66ee703d102153
Author: Andrew Morton <[email protected]>
Date: Wed Feb 25 16:17:36 2004 -0800
[PATCH] HFS rewrite
From: Roman Zippel <[email protected]>
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
point.
Thanks to Ethan Benson <[email protected]> for a number of patches to make
the driver more compliant with the spec and Christoph Hellwig <[email protected]>
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;
On Fri, Nov 23, 2018 at 04:51:49PM -0800, Viacheslav Dubeyko wrote:
> 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>")
> >
> > Signed-off-by: Pan Bian <[email protected]>
> > ---
> > ?fs/hfs/btree.c | 3 ++-
> > ?1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
> > index 98b96ff..19017d2 100644
> > --- 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);
>
>
> What's about simply to store node->this into the local variable in the
> beginning of the cycle? In this case, it is possible to use the node ID
> in the pr_crit() and to use the hfs_bnode_put(node) in the same place
> without to use it twice. What do you think?
Of course, it is a solution. But I think doing like that does not really
simplify the code, as we have to declare an extra local variable, and
assign node->this to it...
Best,
Pan
>
> Thanks,
> Vyacheslav Dubeyko.
>
>
> > + hfs_bnode_put(node);
> > ? return;
> > ? }
> > + hfs_bnode_put(node);
> > ? node = hfs_bnode_find(tree, i);
> > ? if (IS_ERR(node))
> > ? return;
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>")
>
> Signed-off-by: Pan Bian <[email protected]>
> ---
> fs/hfs/btree.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/hfs/btree.c b/fs/hfs/btree.c
> index 98b96ff..19017d2 100644
> --- 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);
What's about simply to store node->this into the local variable in the
beginning of the cycle? In this case, it is possible to use the node ID
in the pr_crit() and to use the hfs_bnode_put(node) in the same place
without to use it twice. What do you think?
Thanks,
Vyacheslav Dubeyko.
> + hfs_bnode_put(node);
> return;
> }
> + hfs_bnode_put(node);
> node = hfs_bnode_find(tree, i);
> if (IS_ERR(node))
> return;