* [PATCH] refcount: add refcount_t API kernel-doc comments
@ 2017-03-03 1:55 David Windsor
2017-03-09 22:58 ` [kernel-hardening] " Kees Cook
2017-03-10 7:25 ` Ingo Molnar
0 siblings, 2 replies; 6+ messages in thread
From: David Windsor @ 2017-03-03 1:55 UTC (permalink / raw)
To: peterz, mingo, elena.reshetova, dwindsor; +Cc: linux-kernel, kernel-hardening
This adds kernel-doc comments for the new refcount_t API.
v2: incorporate fixes from Peter Zijlstra and Ingo Molnar
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
lib/refcount.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 110 insertions(+), 12 deletions(-)
diff --git a/lib/refcount.c b/lib/refcount.c
index 1d33366..d6e317a 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -37,6 +37,24 @@
#include <linux/refcount.h>
#include <linux/bug.h>
+/**
+ * refcount_add_not_zero - add a value to a refcount unless it is 0
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Will saturate at UINT_MAX and WARN.
+ *
+ * Provides no memory ordering, it is assumed the caller has guaranteed the
+ * object memory to be stable (RCU, etc.). It does provide a control dependency
+ * and thereby orders future stores. See the comment on top.
+ *
+ * Use of this function is not recommended for the normal reference counting
+ * use case in which references are taken and released one at a time. In these
+ * cases, refcount_inc(), or one of its variants, should instead be used to
+ * increment a reference count.
+ *
+ * Return: false if the passed refcount is 0, true otherwise
+ */
bool refcount_add_not_zero(unsigned int i, refcount_t *r)
{
unsigned int old, new, val = atomic_read(&r->refs);
@@ -64,18 +82,39 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_add_not_zero);
+/**
+ * refcount_add - add a value to a refcount
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
+ *
+ * Provides no memory ordering, it is assumed the caller has guaranteed the
+ * object memory to be stable (RCU, etc.). It does provide a control dependency
+ * and thereby orders future stores. See the comment on top.
+ *
+ * Use of this function is not recommended for the normal reference counting
+ * use case in which references are taken and released one at a time. In these
+ * cases, refcount_inc(), or one of its variants, should instead be used to
+ * increment a reference count.
+ */
void refcount_add(unsigned int i, refcount_t *r)
{
WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
EXPORT_SYMBOL_GPL(refcount_add);
-/*
- * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
+/**
+ * refcount_inc_not_zero - increment a refcount unless it is 0
+ * @r: the refcount to increment
+ *
+ * Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
* and thereby orders future stores. See the comment on top.
+ *
+ * Return: true if the increment was successful, false otherwise
*/
bool refcount_inc_not_zero(refcount_t *r)
{
@@ -103,11 +142,17 @@ bool refcount_inc_not_zero(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
-/*
- * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
+/**
+ * refcount_inc - increment a refcount
+ * @r: the refcount to increment
+ *
+ * Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
- * reference on the object, will WARN when this is not so.
+ * reference on the object.
+ *
+ * Will WARN if the refcount is 0, as this represents a possible use-after-free
+ * condition.
*/
void refcount_inc(refcount_t *r)
{
@@ -115,6 +160,26 @@ void refcount_inc(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_inc);
+/**
+ * refcount_sub_and_test - subtract from a refcount and test if it is 0
+ * @i: amount to subtract from the refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_dec_and_test(), but it will WARN, return false and
+ * ultimately leak on underflow and will fail to decrement when saturated
+ * at UINT_MAX.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before, and provides a control dependency such that free() must come after.
+ * See the comment on top.
+ *
+ * Use of this function is not recommended for the normal reference counting
+ * use case in which references are taken and released one at a time. In these
+ * cases, refcount_dec(), or one of its variants, should instead be used to
+ * decrement a reference count.
+ *
+ * Return: true if the resulting refcount is 0, false otherwise
+ */
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
{
unsigned int old, new, val = atomic_read(&r->refs);
@@ -140,13 +205,18 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_sub_and_test);
-/*
+/**
+ * refcount_dec_and_test - decrement a refcount and test if it is 0
+ * @r: the refcount
+ *
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true if the resulting refcount is 0, false otherwise
*/
bool refcount_dec_and_test(refcount_t *r)
{
@@ -154,21 +224,26 @@ bool refcount_dec_and_test(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_and_test);
-/*
+/**
+ * refcount_dec - decrement a refcount
+ * @r: the refcount
+ *
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
* when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before.
*/
-
void refcount_dec(refcount_t *r)
{
WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
EXPORT_SYMBOL_GPL(refcount_dec);
-/*
+/**
+ * refcount_dec_if_one - decrement a refcount if it is 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
* success thereof.
*
@@ -178,6 +253,8 @@ EXPORT_SYMBOL_GPL(refcount_dec);
* It can be used like a try-delete operator; this explicit case is provided
* and not cmpxchg in generic, because that would allow implementing unsafe
* operations.
+ *
+ * Return: true if the resulting refcount is 0, false otherwise
*/
bool refcount_dec_if_one(refcount_t *r)
{
@@ -185,11 +262,16 @@ bool refcount_dec_if_one(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_if_one);
-/*
+/**
+ * refcount_dec_not_one - decrement a refcount if it is not 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it decrements unless the value is 1, in which case
* it will return false.
*
* Was often done like: atomic_add_unless(&var, -1, 1)
+ *
+ * Return: true if the decrement operation was successful, false otherwise
*/
bool refcount_dec_not_one(refcount_t *r)
{
@@ -219,13 +301,21 @@ bool refcount_dec_not_one(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_not_one);
-/*
+/**
+ * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the mutex to be locked
+ *
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
* to decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true and hold mutex if able to decrement refcount to 0, false
+ * otherwise
*/
bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
{
@@ -242,13 +332,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
}
EXPORT_SYMBOL_GPL(refcount_dec_and_mutex_lock);
-/*
+/**
+ * refcount_dec_and_lock - return holding spinlock if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the spinlock to be locked
+ *
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true and hold spinlock if able to decrement refcount to 0, false
+ * otherwise
*/
bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
{
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [kernel-hardening] [PATCH] refcount: add refcount_t API kernel-doc comments
2017-03-03 1:55 [PATCH] refcount: add refcount_t API kernel-doc comments David Windsor
@ 2017-03-09 22:58 ` Kees Cook
2017-03-10 7:25 ` Ingo Molnar
1 sibling, 0 replies; 6+ messages in thread
From: Kees Cook @ 2017-03-09 22:58 UTC (permalink / raw)
To: David Windsor
Cc: Peter Zijlstra, Ingo Molnar, Reshetova, Elena, LKML, kernel-hardening
On Thu, Mar 2, 2017 at 5:55 PM, David Windsor <dwindsor@gmail.com> wrote:
> This adds kernel-doc comments for the new refcount_t API.
>
> v2: incorporate fixes from Peter Zijlstra and Ingo Molnar
Thanks for the update!
>
> Signed-off-by: David Windsor <dwindsor@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Can this go via the tip locking tree, or should I take it in my kspp tree?
Thanks,
-Kees
> ---
> lib/refcount.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 110 insertions(+), 12 deletions(-)
>
> diff --git a/lib/refcount.c b/lib/refcount.c
> index 1d33366..d6e317a 100644
> --- a/lib/refcount.c
> +++ b/lib/refcount.c
> @@ -37,6 +37,24 @@
> #include <linux/refcount.h>
> #include <linux/bug.h>
>
> +/**
> + * refcount_add_not_zero - add a value to a refcount unless it is 0
> + * @i: the value to add to the refcount
> + * @r: the refcount
> + *
> + * Will saturate at UINT_MAX and WARN.
> + *
> + * Provides no memory ordering, it is assumed the caller has guaranteed the
> + * object memory to be stable (RCU, etc.). It does provide a control dependency
> + * and thereby orders future stores. See the comment on top.
> + *
> + * Use of this function is not recommended for the normal reference counting
> + * use case in which references are taken and released one at a time. In these
> + * cases, refcount_inc(), or one of its variants, should instead be used to
> + * increment a reference count.
> + *
> + * Return: false if the passed refcount is 0, true otherwise
> + */
> bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -64,18 +82,39 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_add_not_zero);
>
> +/**
> + * refcount_add - add a value to a refcount
> + * @i: the value to add to the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
> + *
> + * Provides no memory ordering, it is assumed the caller has guaranteed the
> + * object memory to be stable (RCU, etc.). It does provide a control dependency
> + * and thereby orders future stores. See the comment on top.
> + *
> + * Use of this function is not recommended for the normal reference counting
> + * use case in which references are taken and released one at a time. In these
> + * cases, refcount_inc(), or one of its variants, should instead be used to
> + * increment a reference count.
> + */
> void refcount_add(unsigned int i, refcount_t *r)
> {
> WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_add);
>
> -/*
> - * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
> +/**
> + * refcount_inc_not_zero - increment a refcount unless it is 0
> + * @r: the refcount to increment
> + *
> + * Similar to atomic_inc_not_zero(), but will saturate at UINT_MAX and WARN.
> *
> * Provides no memory ordering, it is assumed the caller has guaranteed the
> * object memory to be stable (RCU, etc.). It does provide a control dependency
> * and thereby orders future stores. See the comment on top.
> + *
> + * Return: true if the increment was successful, false otherwise
> */
> bool refcount_inc_not_zero(refcount_t *r)
> {
> @@ -103,11 +142,17 @@ bool refcount_inc_not_zero(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
>
> -/*
> - * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
> +/**
> + * refcount_inc - increment a refcount
> + * @r: the refcount to increment
> + *
> + * Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
> *
> * Provides no memory ordering, it is assumed the caller already has a
> - * reference on the object, will WARN when this is not so.
> + * reference on the object.
> + *
> + * Will WARN if the refcount is 0, as this represents a possible use-after-free
> + * condition.
> */
> void refcount_inc(refcount_t *r)
> {
> @@ -115,6 +160,26 @@ void refcount_inc(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc);
>
> +/**
> + * refcount_sub_and_test - subtract from a refcount and test if it is 0
> + * @i: amount to subtract from the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_dec_and_test(), but it will WARN, return false and
> + * ultimately leak on underflow and will fail to decrement when saturated
> + * at UINT_MAX.
> + *
> + * Provides release memory ordering, such that prior loads and stores are done
> + * before, and provides a control dependency such that free() must come after.
> + * See the comment on top.
> + *
> + * Use of this function is not recommended for the normal reference counting
> + * use case in which references are taken and released one at a time. In these
> + * cases, refcount_dec(), or one of its variants, should instead be used to
> + * decrement a reference count.
> + *
> + * Return: true if the resulting refcount is 0, false otherwise
> + */
> bool refcount_sub_and_test(unsigned int i, refcount_t *r)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -140,13 +205,18 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_sub_and_test);
>
> -/*
> +/**
> + * refcount_dec_and_test - decrement a refcount and test if it is 0
> + * @r: the refcount
> + *
> * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
> * decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true if the resulting refcount is 0, false otherwise
> */
> bool refcount_dec_and_test(refcount_t *r)
> {
> @@ -154,21 +224,26 @@ bool refcount_dec_and_test(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_and_test);
>
> -/*
> +/**
> + * refcount_dec - decrement a refcount
> + * @r: the refcount
> + *
> * Similar to atomic_dec(), it will WARN on underflow and fail to decrement
> * when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before.
> */
> -
> void refcount_dec(refcount_t *r)
> {
> WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_dec);
>
> -/*
> +/**
> + * refcount_dec_if_one - decrement a refcount if it is 1
> + * @r: the refcount
> + *
> * No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
> * success thereof.
> *
> @@ -178,6 +253,8 @@ EXPORT_SYMBOL_GPL(refcount_dec);
> * It can be used like a try-delete operator; this explicit case is provided
> * and not cmpxchg in generic, because that would allow implementing unsafe
> * operations.
> + *
> + * Return: true if the resulting refcount is 0, false otherwise
> */
> bool refcount_dec_if_one(refcount_t *r)
> {
> @@ -185,11 +262,16 @@ bool refcount_dec_if_one(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_if_one);
>
> -/*
> +/**
> + * refcount_dec_not_one - decrement a refcount if it is not 1
> + * @r: the refcount
> + *
> * No atomic_t counterpart, it decrements unless the value is 1, in which case
> * it will return false.
> *
> * Was often done like: atomic_add_unless(&var, -1, 1)
> + *
> + * Return: true if the decrement operation was successful, false otherwise
> */
> bool refcount_dec_not_one(refcount_t *r)
> {
> @@ -219,13 +301,21 @@ bool refcount_dec_not_one(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_not_one);
>
> -/*
> +/**
> + * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
> + * refcount to 0
> + * @r: the refcount
> + * @lock: the mutex to be locked
> + *
> * Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
> * to decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true and hold mutex if able to decrement refcount to 0, false
> + * otherwise
> */
> bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
> {
> @@ -242,13 +332,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_and_mutex_lock);
>
> -/*
> +/**
> + * refcount_dec_and_lock - return holding spinlock if able to decrement
> + * refcount to 0
> + * @r: the refcount
> + * @lock: the spinlock to be locked
> + *
> * Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
> * decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true and hold spinlock if able to decrement refcount to 0, false
> + * otherwise
> */
> bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
> {
> --
> 2.7.4
>
--
Kees Cook
Pixel Security
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] refcount: add refcount_t API kernel-doc comments
2017-03-03 1:55 [PATCH] refcount: add refcount_t API kernel-doc comments David Windsor
2017-03-09 22:58 ` [kernel-hardening] " Kees Cook
@ 2017-03-10 7:25 ` Ingo Molnar
1 sibling, 0 replies; 6+ messages in thread
From: Ingo Molnar @ 2017-03-10 7:25 UTC (permalink / raw)
To: David Windsor
Cc: peterz, elena.reshetova, linux-kernel, kernel-hardening, Kees Cook
* David Windsor <dwindsor@gmail.com> wrote:
> This adds kernel-doc comments for the new refcount_t API.
>
> v2: incorporate fixes from Peter Zijlstra and Ingo Molnar
>
> Signed-off-by: David Windsor <dwindsor@gmail.com>
> ---
> lib/refcount.c | 122 +++++++++++++++++++++++++++++++++++++++++++++++++++------
> 1 file changed, 110 insertions(+), 12 deletions(-)
Patch does not apply cleanly anymore, could you please merge it to Linus's latest
and resend?
Thanks!
Ingo
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] refcount: add refcount_t API kernel-doc comments
2017-03-01 3:34 David Windsor
2017-03-01 7:38 ` Ingo Molnar
@ 2017-03-01 8:47 ` Peter Zijlstra
1 sibling, 0 replies; 6+ messages in thread
From: Peter Zijlstra @ 2017-03-01 8:47 UTC (permalink / raw)
To: David Windsor; +Cc: mingo, elena.reshetova, linux-kernel, kernel-hardening
On Tue, Feb 28, 2017 at 10:34:45PM -0500, David Windsor wrote:
> diff --git a/lib/refcount.c b/lib/refcount.c
> index 1d33366..30e0927 100644
> --- a/lib/refcount.c
> +++ b/lib/refcount.c
> @@ -37,6 +37,15 @@
> #include <linux/refcount.h>
> #include <linux/bug.h>
>
> +/**
> + * refcount_add_not_zero - add a value to a refcount unless the refcount is 0
> + * @i: the value to add to the refcount
> + * @r: the refcount
> + *
> + * Will saturate at UINT_MAX and WARN.
> + *
> + * Return: false if the refcount is 0, true otherwise.
> + */
> bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -64,18 +73,30 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_add_not_zero);
>
> +/**
> + * refcount_add - add a value to a refcount
> + * @i: the value to add to the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_add(), will saturate at UINT_MAX and WARN.
> + */
> void refcount_add(unsigned int i, refcount_t *r)
> {
> WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_add);
Usage of both of these should be discouraged, add/sub on refcounts is
'odd'. Also, both these lack the comment on memory ordering, copy/paste
from inc_not_zero/inc.
> -/*
> +/**
> + * refcount_inc_not_zero - increment a refcount unless it is 0
> + * @r: the refcount to increment
> + *
> * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
> *
> * Provides no memory ordering, it is assumed the caller has guaranteed the
> * object memory to be stable (RCU, etc.). It does provide a control dependency
> * and thereby orders future stores. See the comment on top.
> + *
> + * Return: false if the refcount is 0, true otherwise
An alternative interpretation is: return true if the increment happened,
false otherwise. But given the saturation semantics that might be
awkward, but its the one I find easier to work with.
> */
> bool refcount_inc_not_zero(refcount_t *r)
> {
> @@ -103,11 +124,16 @@ bool refcount_inc_not_zero(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
>
> -/*
> +/**
> + * refcount_inc - increment a refcount
> + * @r: the refcount to increment
> + *
> * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
> *
> * Provides no memory ordering, it is assumed the caller already has a
> * reference on the object, will WARN when this is not so.
> + *
> + * Will WARN if refcount is 0.
I think that duplicates the final part of the prior sentence in intent.
Also, it might be useful to explain why.
> */
> void refcount_inc(refcount_t *r)
> {
> @@ -115,6 +141,22 @@ void refcount_inc(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc);
>
> +/**
> + * refcount_sub_and_test - subtract from a refcount and test if it is 0
> + * @i: amount to subtract from the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
> + * decrement when saturated at UINT_MAX.
It will equally fail the subtraction on underflow and return false
(didn't hit 0) and leak.
> + *
> + * Provides release memory ordering, such that prior loads and stores are done
> + * before, and provides a control dependency such that free() must come after.
> + * See the comment on top.
> + *
> + * Return: true if the resulting refcount is greater than 0, false if the
> + * resulting refcount is 0, the refcount is saturated at UINT_MAX or the
> + * subtraction operation causes an underflow.
I think you got that wrong, will return true when we hit 0, false
otherwise.
Remember; one writes:
if (dec_and_test(&obj->ref))
free(obj);
> + */
> bool refcount_sub_and_test(unsigned int i, refcount_t *r)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -140,13 +182,20 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_sub_and_test);
As with add, sub should be discouraged.
> -/*
> +/**
> + * refcount_dec_and_test - decrement a refcount and test if it is 0
> + * @r: the refcount
> + *
> * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
> * decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true if the resulting refcount is greater than 0, false if the
> + * resulting refcount is 0, the refcount is saturated at UINT_MAX or the
> + * decrement operation causes an underflow.
got that similarly wrong.
> */
> bool refcount_dec_and_test(refcount_t *r)
> {
> @@ -154,21 +203,26 @@ bool refcount_dec_and_test(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_and_test);
>
> -/*
> +/**
> + * refcount_dec - decrement a refcount
> + * @r: the refcount
> + *
> * Similar to atomic_dec(), it will WARN on underflow and fail to decrement
> * when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before.
> */
> -
> void refcount_dec(refcount_t *r)
> {
> WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_dec);
>
> -/*
> +/**
> + * refcount_dec_if_one - decrement a refcount if it is 1
> + * @r: the refcount
> + *
> * No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
> * success thereof.
> *
> @@ -178,6 +232,8 @@ EXPORT_SYMBOL_GPL(refcount_dec);
> * It can be used like a try-delete operator; this explicit case is provided
> * and not cmpxchg in generic, because that would allow implementing unsafe
> * operations.
> + *
> + * Return: true if the 1 -> 0 transition was successful, false otherwise
I'd formulate it differently, to match dec_and_test, return true if 0.
> */
> bool refcount_dec_if_one(refcount_t *r)
> {
> @@ -185,11 +241,16 @@ bool refcount_dec_if_one(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_if_one);
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] refcount: add refcount_t API kernel-doc comments
2017-03-01 3:34 David Windsor
@ 2017-03-01 7:38 ` Ingo Molnar
2017-03-01 8:47 ` Peter Zijlstra
1 sibling, 0 replies; 6+ messages in thread
From: Ingo Molnar @ 2017-03-01 7:38 UTC (permalink / raw)
To: David Windsor; +Cc: peterz, elena.reshetova, linux-kernel, kernel-hardening
* David Windsor <dwindsor@gmail.com> wrote:
> This adds kernel-doc comments for the new refcount_t API.
>
> Signed-off-by: David Windsor <dwindsor@gmail.com>
> ---
> include/linux/refcount.h | 19 ++++++++++
> lib/refcount.c | 95 +++++++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 105 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> index 0023fee..3c02135 100644
> --- a/include/linux/refcount.h
> +++ b/include/linux/refcount.h
> @@ -6,17 +6,36 @@
> #include <linux/spinlock.h>
> #include <linux/kernel.h>
>
> +/**
> + * refcount_t - variant of atomic_t specialized for reference counts
> + * @refs: atomic_t counter field
> + *
> + * The counter saturates at UINT_MAX and will not move once
> + * there. This avoids wrapping the counter and causing 'spurious'
> + * use-after-free issues.
Let's not beat around the bush:
s/issues/bugs
> +/**
> + * refcount_add - add a value to a refcount
> + * @i: the value to add to the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_add(), will saturate at UINT_MAX and WARN.
I realize you picked it up from the existing comments, but if we push this into
docbook I'd phrase it this way:
* Similar to atomic_add(), but will saturate at UINT_MAX and WARN.
(The 'but' contasts the main difference to atomic_add().)
> + */
> void refcount_add(unsigned int i, refcount_t *r)
> {
> WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
> }
> EXPORT_SYMBOL_GPL(refcount_add);
>
> -/*
> +/**
> + * refcount_inc_not_zero - increment a refcount unless it is 0
> + * @r: the refcount to increment
So this is slightly different from the phrasing earlier on:
+/**
+ * refcount_add_not_zero - add a value to a refcount unless the refcount is 0
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
Please harmonize it: either use 'a refcount unless it is 0' or 'a refcount unless
the refcount is 0' - but not a mixture of the two.
Same goes for similar occurances further below.
> + *
> * Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
This should be updated similarly as above.
> *
> * Provides no memory ordering, it is assumed the caller has guaranteed the
> * object memory to be stable (RCU, etc.). It does provide a control dependency
> * and thereby orders future stores. See the comment on top.
> + *
> + * Return: false if the refcount is 0, true otherwise
> */
> bool refcount_inc_not_zero(refcount_t *r)
> {
> @@ -103,11 +124,16 @@ bool refcount_inc_not_zero(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
>
> -/*
> +/**
> + * refcount_inc - increment a refcount
> + * @r: the refcount to increment
> + *
> * Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
> *
> * Provides no memory ordering, it is assumed the caller already has a
> * reference on the object, will WARN when this is not so.
> + *
> + * Will WARN if refcount is 0.
s/if refcount/if the refcount
> */
> void refcount_inc(refcount_t *r)
> {
> @@ -115,6 +141,22 @@ void refcount_inc(refcount_t *r)
> }
> EXPORT_SYMBOL_GPL(refcount_inc);
>
> +/**
> + * refcount_sub_and_test - subtract from a refcount and test if it is 0
> + * @i: amount to subtract from the refcount
> + * @r: the refcount
> + *
> + * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
> + * decrement when saturated at UINT_MAX.
I'd insert the 'but' here too to highlight differences to the atomic APIs.
> +/**
> + * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
> + * refcount to 0
> + * @r: the refcount
> + * @lock: the mutex to be locked
> + *
> * Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
> * to decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true and hold lock if able to decrement refcount to 0, false
> + * otherwise
If we refer to a function parameter then it should be quoted as 'lock', but what
mean here is that we'll hold the mutex:
s/lock/mutex
> */
> bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
> {
> @@ -242,13 +311,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
> }
> EXPORT_SYMBOL_GPL(refcount_dec_and_mutex_lock);
>
> -/*
> +/**
> + * refcount_dec_and_lock - return holding spinlock if able to decrement
> + * refcount to 0
> + * @r: the refcount
> + * @lock: the spinlock to be locked
> + *
> * Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
> * decrement when saturated at UINT_MAX.
> *
> * Provides release memory ordering, such that prior loads and stores are done
> * before, and provides a control dependency such that free() must come after.
> * See the comment on top.
> + *
> + * Return: true and hold lock if able to decrement refcount to 0, false
> + * otherwise
s/lock/spinlock
Looks good otherwise and thanks for the documentation update!
Thanks,
Ingo
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH] refcount: add refcount_t API kernel-doc comments
@ 2017-03-01 3:34 David Windsor
2017-03-01 7:38 ` Ingo Molnar
2017-03-01 8:47 ` Peter Zijlstra
0 siblings, 2 replies; 6+ messages in thread
From: David Windsor @ 2017-03-01 3:34 UTC (permalink / raw)
To: peterz, mingo, elena.reshetova, dwindsor; +Cc: linux-kernel, kernel-hardening
This adds kernel-doc comments for the new refcount_t API.
Signed-off-by: David Windsor <dwindsor@gmail.com>
---
include/linux/refcount.h | 19 ++++++++++
lib/refcount.c | 95 +++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 105 insertions(+), 9 deletions(-)
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 0023fee..3c02135 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -6,17 +6,36 @@
#include <linux/spinlock.h>
#include <linux/kernel.h>
+/**
+ * refcount_t - variant of atomic_t specialized for reference counts
+ * @refs: atomic_t counter field
+ *
+ * The counter saturates at UINT_MAX and will not move once
+ * there. This avoids wrapping the counter and causing 'spurious'
+ * use-after-free issues.
+ */
typedef struct refcount_struct {
atomic_t refs;
} refcount_t;
#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
+/**
+ * refcount_set - set a refcount's value
+ * @r: the refcount
+ * @n: value to which the refcount will be set
+ */
static inline void refcount_set(refcount_t *r, unsigned int n)
{
atomic_set(&r->refs, n);
}
+/**
+ * refcount_read - get a refcount's value
+ * @r: the refcount
+ *
+ * Return: the refcount's value
+ */
static inline unsigned int refcount_read(const refcount_t *r)
{
return atomic_read(&r->refs);
diff --git a/lib/refcount.c b/lib/refcount.c
index 1d33366..30e0927 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -37,6 +37,15 @@
#include <linux/refcount.h>
#include <linux/bug.h>
+/**
+ * refcount_add_not_zero - add a value to a refcount unless the refcount is 0
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Will saturate at UINT_MAX and WARN.
+ *
+ * Return: false if the refcount is 0, true otherwise.
+ */
bool refcount_add_not_zero(unsigned int i, refcount_t *r)
{
unsigned int old, new, val = atomic_read(&r->refs);
@@ -64,18 +73,30 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_add_not_zero);
+/**
+ * refcount_add - add a value to a refcount
+ * @i: the value to add to the refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_add(), will saturate at UINT_MAX and WARN.
+ */
void refcount_add(unsigned int i, refcount_t *r)
{
WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
EXPORT_SYMBOL_GPL(refcount_add);
-/*
+/**
+ * refcount_inc_not_zero - increment a refcount unless it is 0
+ * @r: the refcount to increment
+ *
* Similar to atomic_inc_not_zero(), will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller has guaranteed the
* object memory to be stable (RCU, etc.). It does provide a control dependency
* and thereby orders future stores. See the comment on top.
+ *
+ * Return: false if the refcount is 0, true otherwise
*/
bool refcount_inc_not_zero(refcount_t *r)
{
@@ -103,11 +124,16 @@ bool refcount_inc_not_zero(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_inc_not_zero);
-/*
+/**
+ * refcount_inc - increment a refcount
+ * @r: the refcount to increment
+ *
* Similar to atomic_inc(), will saturate at UINT_MAX and WARN.
*
* Provides no memory ordering, it is assumed the caller already has a
* reference on the object, will WARN when this is not so.
+ *
+ * Will WARN if refcount is 0.
*/
void refcount_inc(refcount_t *r)
{
@@ -115,6 +141,22 @@ void refcount_inc(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_inc);
+/**
+ * refcount_sub_and_test - subtract from a refcount and test if it is 0
+ * @i: amount to subtract from the refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
+ * decrement when saturated at UINT_MAX.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before, and provides a control dependency such that free() must come after.
+ * See the comment on top.
+ *
+ * Return: true if the resulting refcount is greater than 0, false if the
+ * resulting refcount is 0, the refcount is saturated at UINT_MAX or the
+ * subtraction operation causes an underflow.
+ */
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
{
unsigned int old, new, val = atomic_read(&r->refs);
@@ -140,13 +182,20 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_sub_and_test);
-/*
+/**
+ * refcount_dec_and_test - decrement a refcount and test if it is 0
+ * @r: the refcount
+ *
* Similar to atomic_dec_and_test(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true if the resulting refcount is greater than 0, false if the
+ * resulting refcount is 0, the refcount is saturated at UINT_MAX or the
+ * decrement operation causes an underflow.
*/
bool refcount_dec_and_test(refcount_t *r)
{
@@ -154,21 +203,26 @@ bool refcount_dec_and_test(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_and_test);
-/*
+/**
+ * refcount_dec - decrement a refcount
+ * @r: the refcount
+ *
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
* when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before.
*/
-
void refcount_dec(refcount_t *r)
{
WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
EXPORT_SYMBOL_GPL(refcount_dec);
-/*
+/**
+ * refcount_dec_if_one - decrement a refcount if it is 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it attempts a 1 -> 0 transition and returns the
* success thereof.
*
@@ -178,6 +232,8 @@ EXPORT_SYMBOL_GPL(refcount_dec);
* It can be used like a try-delete operator; this explicit case is provided
* and not cmpxchg in generic, because that would allow implementing unsafe
* operations.
+ *
+ * Return: true if the 1 -> 0 transition was successful, false otherwise
*/
bool refcount_dec_if_one(refcount_t *r)
{
@@ -185,11 +241,16 @@ bool refcount_dec_if_one(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_if_one);
-/*
+/**
+ * refcount_dec_not_one - decrement a refcount if it is not 1
+ * @r: the refcount
+ *
* No atomic_t counterpart, it decrements unless the value is 1, in which case
* it will return false.
*
* Was often done like: atomic_add_unless(&var, -1, 1)
+ *
+ * Return: true if the decrement operation was successful, false otherwise
*/
bool refcount_dec_not_one(refcount_t *r)
{
@@ -219,13 +280,21 @@ bool refcount_dec_not_one(refcount_t *r)
}
EXPORT_SYMBOL_GPL(refcount_dec_not_one);
-/*
+/**
+ * refcount_dec_and_mutex_lock - return holding mutex if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the mutex to be locked
+ *
* Similar to atomic_dec_and_mutex_lock(), it will WARN on underflow and fail
* to decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true and hold lock if able to decrement refcount to 0, false
+ * otherwise
*/
bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
{
@@ -242,13 +311,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
}
EXPORT_SYMBOL_GPL(refcount_dec_and_mutex_lock);
-/*
+/**
+ * refcount_dec_and_lock - return holding spinlock if able to decrement
+ * refcount to 0
+ * @r: the refcount
+ * @lock: the spinlock to be locked
+ *
* Similar to atomic_dec_and_lock(), it will WARN on underflow and fail to
* decrement when saturated at UINT_MAX.
*
* Provides release memory ordering, such that prior loads and stores are done
* before, and provides a control dependency such that free() must come after.
* See the comment on top.
+ *
+ * Return: true and hold lock if able to decrement refcount to 0, false
+ * otherwise
*/
bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
{
--
2.7.4
^ permalink raw reply related [flat|nested] 6+ messages in thread
end of thread, other threads:[~2017-03-10 7:25 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
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2017-03-03 1:55 [PATCH] refcount: add refcount_t API kernel-doc comments David Windsor
2017-03-09 22:58 ` [kernel-hardening] " Kees Cook
2017-03-10 7:25 ` Ingo Molnar
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2017-03-01 7:38 ` Ingo Molnar
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