From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Windsor Date: Wed, 8 Feb 2017 10:54:58 -0500 Message-Id: <1486569298-5157-1-git-send-email-dwindsor@gmail.com> Subject: [kernel-hardening] [PATCH v2] refcount: add refcount_t API kernel-doc comments To: kernel-hardening@lists.openwall.com, peterz@infradead.org, elena.reshetova@intel.com Cc: keescook@chromium.org, ishkamiel@gmail.com, dwindsor@gmail.com List-ID: 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 --- 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