| Message ID | 1488339285-23777-1-git-send-email-dwindsor@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, Feb 28, 2017 at 7:34 PM, 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> Yay docs! :) Acked-by: Kees Cook <keescook@chromium.org> -Kees
* 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
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);
On Tue, Feb 28, 2017 at 09:44:40PM -0800, Kees Cook wrote: > On Tue, Feb 28, 2017 at 7:34 PM, 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> > > Yay docs! :) > > Acked-by: Kees Cook <keescook@chromium.org> Now if only they were accurate ;-)
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) {
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(-)