* [PATCH] idr: Prevent unintended underflow for the idr index
@ 2019-09-17 21:48 Jordan Crouse
2019-09-18 11:50 ` Matthew Wilcox
0 siblings, 1 reply; 3+ messages in thread
From: Jordan Crouse @ 2019-09-17 21:48 UTC (permalink / raw)
To: freedreno; +Cc: linux-arm-msm, linux-fsdevel, Matthew Wilcox, linux-kernel
It is possible for unaware callers of several idr functions to accidentally
underflow the index by specifying a id that is less than the idr base.
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
---
lib/idr.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/lib/idr.c b/lib/idr.c
index 66a3748..d9e180c 100644
--- a/lib/idr.c
+++ b/lib/idr.c
@@ -151,6 +151,9 @@ EXPORT_SYMBOL(idr_alloc_cyclic);
*/
void *idr_remove(struct idr *idr, unsigned long id)
{
+ if (id < idr->idr_base)
+ return NULL;
+
return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
}
EXPORT_SYMBOL_GPL(idr_remove);
@@ -171,6 +174,9 @@ EXPORT_SYMBOL_GPL(idr_remove);
*/
void *idr_find(const struct idr *idr, unsigned long id)
{
+ if (id < idr->idr_base)
+ return NULL;
+
return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
}
EXPORT_SYMBOL_GPL(idr_find);
@@ -302,6 +308,9 @@ void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
void __rcu **slot = NULL;
void *entry;
+ if (id < idr->idr_base)
+ return ERR_PTR(-ENOENT);
+
id -= idr->idr_base;
entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
--
2.7.4
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] idr: Prevent unintended underflow for the idr index
2019-09-17 21:48 [PATCH] idr: Prevent unintended underflow for the idr index Jordan Crouse
@ 2019-09-18 11:50 ` Matthew Wilcox
2019-09-18 15:32 ` Jordan Crouse
0 siblings, 1 reply; 3+ messages in thread
From: Matthew Wilcox @ 2019-09-18 11:50 UTC (permalink / raw)
To: Jordan Crouse; +Cc: freedreno, linux-arm-msm, linux-fsdevel, linux-kernel
On Tue, Sep 17, 2019 at 03:48:42PM -0600, Jordan Crouse wrote:
> It is possible for unaware callers of several idr functions to accidentally
> underflow the index by specifying a id that is less than the idr base.
Hi Jordan. Thanks for the patch, but this seems like a distinction
without a difference.
> void *idr_remove(struct idr *idr, unsigned long id)
> {
> + if (id < idr->idr_base)
> + return NULL;
> +
> return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
If this underflows, we'll try to delete an index which doesn't exist,
which will return NULL.
> void *idr_find(const struct idr *idr, unsigned long id)
> {
> + if (id < idr->idr_base)
> + return NULL;
> +
> return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
If this underflows, we'll look up an entry which doesn't exist, which
will return NULL.
> @@ -302,6 +308,9 @@ void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
> void __rcu **slot = NULL;
> void *entry;
>
> + if (id < idr->idr_base)
> + return ERR_PTR(-ENOENT);
> +
> id -= idr->idr_base;
>
> entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
... just outside the context is this line:
if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
return ERR_PTR(-ENOENT);
Looking up an index which doesn't exist gets you a NULL slot, so you get
-ENOENT anyway.
I did think about these possibilities when I was writing the code and
convinced myself I didn't need them. If you have an example of a case
where I got thast wrong, I'd love to see it.
More generally, the IDR is deprecated; I'm trying to convert users to
the XArray. If you're adding a new user, can you use the XArray API
instead?
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] idr: Prevent unintended underflow for the idr index
2019-09-18 11:50 ` Matthew Wilcox
@ 2019-09-18 15:32 ` Jordan Crouse
0 siblings, 0 replies; 3+ messages in thread
From: Jordan Crouse @ 2019-09-18 15:32 UTC (permalink / raw)
To: Matthew Wilcox; +Cc: freedreno, linux-arm-msm, linux-fsdevel, linux-kernel
On Wed, Sep 18, 2019 at 04:50:58AM -0700, Matthew Wilcox wrote:
> On Tue, Sep 17, 2019 at 03:48:42PM -0600, Jordan Crouse wrote:
> > It is possible for unaware callers of several idr functions to accidentally
> > underflow the index by specifying a id that is less than the idr base.
>
> Hi Jordan. Thanks for the patch, but this seems like a distinction
> without a difference.
>
> > void *idr_remove(struct idr *idr, unsigned long id)
> > {
> > + if (id < idr->idr_base)
> > + return NULL;
> > +
> > return radix_tree_delete_item(&idr->idr_rt, id - idr->idr_base, NULL);
>
> If this underflows, we'll try to delete an index which doesn't exist,
> which will return NULL.
>
> > void *idr_find(const struct idr *idr, unsigned long id)
> > {
> > + if (id < idr->idr_base)
> > + return NULL;
> > +
> > return radix_tree_lookup(&idr->idr_rt, id - idr->idr_base);
>
> If this underflows, we'll look up an entry which doesn't exist, which
> will return NULL.
>
> > @@ -302,6 +308,9 @@ void *idr_replace(struct idr *idr, void *ptr, unsigned long id)
> > void __rcu **slot = NULL;
> > void *entry;
> >
> > + if (id < idr->idr_base)
> > + return ERR_PTR(-ENOENT);
> > +
> > id -= idr->idr_base;
> >
> > entry = __radix_tree_lookup(&idr->idr_rt, id, &node, &slot);
>
> ... just outside the context is this line:
> if (!slot || radix_tree_tag_get(&idr->idr_rt, id, IDR_FREE))
> return ERR_PTR(-ENOENT);
>
> Looking up an index which doesn't exist gets you a NULL slot, so you get
> -ENOENT anyway.
>
> I did think about these possibilities when I was writing the code and
> convinced myself I didn't need them. If you have an example of a case
> where I got thast wrong, I'd love to see it.
>
> More generally, the IDR is deprecated; I'm trying to convert users to
> the XArray. If you're adding a new user, can you use the XArray API
> instead?
Thanks for the explanation. I happened to walk by while code inspecting an
existing out-of-tree user and thought there might be a small hole to fill
but I agree it is unlikely that the underflow is likely to be a valid id.
Jordan
--
The Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-09-17 21:48 [PATCH] idr: Prevent unintended underflow for the idr index Jordan Crouse
2019-09-18 11:50 ` Matthew Wilcox
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