v3: rebase against latest Linus tree; re-add include/linux/refcount.h
missing from v2 series
Signed-off-by: David Windsor <[email protected]>
---
include/linux/refcount.h | 19 ++++++++
lib/refcount.c | 124 ++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 130 insertions(+), 13 deletions(-)
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 0023fee..b34aa64 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 bugs.
+ */
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 aa09ad3..8d5d680 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);
@@ -64,19 +82,40 @@ 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_ONCE(!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)
{
unsigned int old, new, val = atomic_read(&r->refs);
@@ -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_ONCE(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
Commit-ID: bd174169c7a12a37b3b4aa2221f084ade010b182
Gitweb: http://git.kernel.org/tip/bd174169c7a12a37b3b4aa2221f084ade010b182
Author: David Windsor <[email protected]>
AuthorDate: Fri, 10 Mar 2017 10:34:12 -0500
Committer: Ingo Molnar <[email protected]>
CommitDate: Mon, 13 Mar 2017 07:41:08 +0100
locking/refcount: Add refcount_t API kernel-doc comments
Signed-off-by: David Windsor <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
---
include/linux/refcount.h | 19 ++++++++
lib/refcount.c | 122 ++++++++++++++++++++++++++++++++++++++++++-----
2 files changed, 129 insertions(+), 12 deletions(-)
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 0023fee..b34aa64 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 bugs.
+ */
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 aa09ad3..8e206ce5 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_ONCE(!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_ONCE(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)
{
On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <[email protected]> wrote:
> v3: rebase against latest Linus tree; re-add include/linux/refcount.h
> missing from v2 series
>
> Signed-off-by: David Windsor <[email protected]>
Reviewed-by: Kees Cook <[email protected]>
Ingo, can you pull this into tip? I like having more documentation here. :)
-Kees
> ---
> include/linux/refcount.h | 19 ++++++++
> lib/refcount.c | 124 ++++++++++++++++++++++++++++++++++++++++++-----
> 2 files changed, 130 insertions(+), 13 deletions(-)
>
> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> index 0023fee..b34aa64 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 bugs.
> + */
> 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 aa09ad3..8d5d680 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);
> @@ -64,19 +82,40 @@ 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_ONCE(!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)
> {
> unsigned int old, new, val = atomic_read(&r->refs);
> @@ -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_ONCE(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
* Kees Cook <[email protected]> wrote:
> On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <[email protected]> wrote:
> > v3: rebase against latest Linus tree; re-add include/linux/refcount.h
> > missing from v2 series
> >
> > Signed-off-by: David Windsor <[email protected]>
>
> Reviewed-by: Kees Cook <[email protected]>
>
> Ingo, can you pull this into tip? I like having more documentation here. :)
So I hopped into my time machine and applied it to tip:locking/core as of March
13th:
commit bd174169c7a12a37b3b4aa2221f084ade010b182
Author: David Windsor <[email protected]>
AuthorDate: Fri Mar 10 10:34:12 2017 -0500
Commit: Ingo Molnar <[email protected]>
CommitDate: Mon Mar 13 07:41:08 2017 +0100
You are welcome! ;-)
Thanks,
Ingo
On Thu, Mar 23, 2017 at 12:40 AM, Ingo Molnar <[email protected]> wrote:
>
> * Kees Cook <[email protected]> wrote:
>
>> On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <[email protected]> wrote:
>> > v3: rebase against latest Linus tree; re-add include/linux/refcount.h
>> > missing from v2 series
>> >
>> > Signed-off-by: David Windsor <[email protected]>
>>
>> Reviewed-by: Kees Cook <[email protected]>
>>
>> Ingo, can you pull this into tip? I like having more documentation here. :)
>
> So I hopped into my time machine and applied it to tip:locking/core as of March
> 13th:
>
> commit bd174169c7a12a37b3b4aa2221f084ade010b182
> Author: David Windsor <[email protected]>
> AuthorDate: Fri Mar 10 10:34:12 2017 -0500
> Commit: Ingo Molnar <[email protected]>
> CommitDate: Mon Mar 13 07:41:08 2017 +0100
>
> You are welcome! ;-)
I love time-travelling maintainers! They are very tolerant of people
who don't double-check -next first. :)
Thanks!
-Kees
--
Kees Cook
Pixel Security