| Message ID | 1568756922-2829-1-git-send-email-jcrouse@codeaurora.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | idr: Prevent unintended underflow for the idr index | expand |
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?
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
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);
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(+)