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Message-Id: <1486569298-5157-1-git-send-email-dwindsor@gmail.com>
Date: Wed, 8 Feb 2017 10:54:58 -0500
From: David Windsor <dwindsor@...il.com>
To: kernel-hardening@...ts.openwall.com,
peterz@...radead.org,
elena.reshetova@...el.com
Cc: keescook@...omium.org,
ishkamiel@...il.com,
dwindsor@...il.com
Subject: [PATCH v2] refcount: add refcount_t API kernel-doc comments
This adds kernel-doc comments for the new refcount_t API. Additional
feature documentation can go in Documentation/security, if needed.
v2: Rebased against PeterZ's refcount series
Signed-off-by: David Windsor <dwindsor@...il.com>
---
include/linux/refcount.h | 111 ++++++++++++++++++++++++++++++++++++++++++-----
1 file changed, 101 insertions(+), 10 deletions(-)
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 5b89cad..82adf2b 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -50,22 +50,50 @@
#define __refcount_check
#endif
+/**
+ * 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 internal counter
+ * @r: the refcount
+ * @n: value to which internal counter 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 internal counter
+ * @r: the refcount
+ *
+ * Return: the value of the refcount's internal counter
+ */
static inline unsigned int refcount_read(const refcount_t *r)
{
return atomic_read(&r->refs);
}
+/**
+ * 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.
+ */
static inline __refcount_check
bool refcount_add_not_zero(unsigned int i, refcount_t *r)
{
@@ -91,17 +119,29 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)
return true;
}
+/**
+ * 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.
+ */
static inline void refcount_add(unsigned int i, refcount_t *r)
{
REFCOUNT_WARN(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
-/*
+/**
+ * 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
*/
static inline __refcount_check
bool refcount_inc_not_zero(refcount_t *r)
@@ -126,24 +166,37 @@ bool refcount_inc_not_zero(refcount_t *r)
return true;
}
-/*
+/**
+ * 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.
*/
static inline void refcount_inc(refcount_t *r)
{
REFCOUNT_WARN(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
}
-/*
+/**
+ * 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.
*/
static inline __refcount_check
bool refcount_sub_and_test(unsigned int i, refcount_t *r)
@@ -167,18 +220,30 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)
return !new;
}
+/**
+ * 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.
+ *
+ * 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.
+ */
static inline __refcount_check
bool refcount_dec_and_test(refcount_t *r)
{
return refcount_sub_and_test(1, r);
}
-/*
+/**
+ * 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.
*/
static inline
void refcount_dec(refcount_t *r)
@@ -186,7 +251,10 @@ void refcount_dec(refcount_t *r)
REFCOUNT_WARN(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
-/*
+/**
+ * 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.
*
@@ -196,6 +264,8 @@ void refcount_dec(refcount_t *r)
* 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 refcount was decremented, false otherwise
*/
static inline __refcount_check
bool refcount_dec_if_one(refcount_t *r)
@@ -205,11 +275,16 @@ bool refcount_dec_if_one(refcount_t *r)
return atomic_try_cmpxchg_release(&r->refs, &val, 0);
}
-/*
+/**
+ * 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: false if the refcount was 1, true otherwise
*/
static inline __refcount_check
bool refcount_dec_not_one(refcount_t *r)
@@ -236,13 +311,21 @@ bool refcount_dec_not_one(refcount_t *r)
return true;
}
-/*
+/**
+ * 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
*/
static inline __refcount_check
bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
@@ -259,13 +342,21 @@ bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock)
return true;
}
-/*
+/**
+ * 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
*/
static inline __refcount_check
bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock)
--
2.7.4
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