From patchwork Wed Mar 1 03:34:45 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: David Windsor X-Patchwork-Id: 9597395 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id C41E660414 for ; Wed, 1 Mar 2017 03:35:11 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id BC8B828452 for ; Wed, 1 Mar 2017 03:35:11 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id B14C6284DA; Wed, 1 Mar 2017 03:35:11 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.1 required=2.0 tests=BAYES_00, DKIM_ADSP_CUSTOM_MED, DKIM_SIGNED, FREEMAIL_FROM, RCVD_IN_DNSWL_MED, T_DKIM_INVALID autolearn=ham version=3.3.1 Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.wl.linuxfoundation.org (Postfix) with SMTP id 58A0328452 for ; Wed, 1 Mar 2017 03:35:09 +0000 (UTC) Received: (qmail 1702 invoked by uid 550); 1 Mar 2017 03:35:07 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Delivered-To: mailing list kernel-hardening@lists.openwall.com Received: (qmail 1657 invoked from network); 1 Mar 2017 03:35:06 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id; bh=QkGJiec5mlUhjs9RPUqH8m15xgj6c00EqLItt/iy/rA=; b=jIpwhS1kjEa8tsu6Dvw2N6993clKBqeWMpD2lKOxgVqMumGBE1wXPcMiaKl4kjeiVQ IVWw9+hB/FtL9rqLesShsbYn9oxB1p7goPEGGXmfbiaCtOOOJlhkaIf17gI6L5hXR1jz REH775/zj9xvwxmrSpJCVsMho38cM4hg3hQOqzl7hQRpEGRjeJjDeSa0R/roY+JOF3Tz xM5urAYCC89hPzo3cKTxIUFOa/eywm80aNj5s0IHOYUWi6rIukZtnu1HxwVxyf3+3xv2 u/iNVXYdBmnuWrd9pwlPJWPEJu4DXv1HlPP9js+vlff8KPhBvjROR4rCdLaipYrR8TMp HqNQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id; bh=QkGJiec5mlUhjs9RPUqH8m15xgj6c00EqLItt/iy/rA=; b=JR4QGAYSLnvf8MF3hsoCfLvXUnqWW6uV4ftgi6ybb7DNBKkvO458+Z459ejwLc4WRL ksLbzI9+XLGT94eA8WD2l6zELq5VJo8asItZfDE7yl9DTPnS3jKY+7LcvRzZ1OqVmG5U taBENnnPRf76VZR50zp2D/Die9K39uYgQhXc8jPWreX3dAzg/Cp4iIjUfxNb0Sw4WS+e dW3sy3NziR1aLUcg9WfW47cj6lu6GIEAdEoQ8ff04b9MT2L5nZsDfbyDJ1ncZtM5xw3k VCWSF1Hge16u80oCFyoOAB2h4RI5DWyuJhXeyHb/k0t9tPlv1y+nr7WJJF2ddNGme+4X j+Gw== X-Gm-Message-State: AMke39kLVSWep7ofiCeyzf0nQV7T/S7gufL9LKFJhiso4mGQeFez/8tvI4W7E5Z4+NB1Og== X-Received: by 10.37.165.102 with SMTP id h93mr2046432ybi.48.1488339293956; Tue, 28 Feb 2017 19:34:53 -0800 (PST) From: David Windsor To: peterz@infradead.org, mingo@kernel.org, elena.reshetova@intel.com, dwindsor@gmail.com Cc: linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com Date: Tue, 28 Feb 2017 22:34:45 -0500 Message-Id: <1488339285-23777-1-git-send-email-dwindsor@gmail.com> X-Mailer: git-send-email 2.7.4 Subject: [kernel-hardening] [PATCH] refcount: add refcount_t API kernel-doc comments X-Virus-Scanned: ClamAV using ClamSMTP This adds kernel-doc comments for the new refcount_t API. Signed-off-by: David Windsor Acked-by: Kees Cook --- 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 #include +/** + * 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 #include +/** + * 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) {