| Message ID | 1489160052-20293-1-git-send-email-dwindsor@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
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On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <dwindsor@gmail.com> wrote: > v3: rebase against latest Linus tree; re-add include/linux/refcount.h > missing from v2 series > > Signed-off-by: David Windsor <dwindsor@gmail.com> Reviewed-by: Kees Cook <keescook@chromium.org> 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 <keescook@chromium.org> wrote: > On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <dwindsor@gmail.com> wrote: > > v3: rebase against latest Linus tree; re-add include/linux/refcount.h > > missing from v2 series > > > > Signed-off-by: David Windsor <dwindsor@gmail.com> > > Reviewed-by: Kees Cook <keescook@chromium.org> > > 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 <dwindsor@gmail.com> AuthorDate: Fri Mar 10 10:34:12 2017 -0500 Commit: Ingo Molnar <mingo@kernel.org> 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 <mingo@kernel.org> wrote: > > * Kees Cook <keescook@chromium.org> wrote: > >> On Fri, Mar 10, 2017 at 7:34 AM, David Windsor <dwindsor@gmail.com> wrote: >> > v3: rebase against latest Linus tree; re-add include/linux/refcount.h >> > missing from v2 series >> > >> > Signed-off-by: David Windsor <dwindsor@gmail.com> >> >> Reviewed-by: Kees Cook <keescook@chromium.org> >> >> 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 <dwindsor@gmail.com> > AuthorDate: Fri Mar 10 10:34:12 2017 -0500 > Commit: Ingo Molnar <mingo@kernel.org> > 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
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) {
v3: rebase against latest Linus tree; re-add include/linux/refcount.h missing from v2 series Signed-off-by: David Windsor <dwindsor@gmail.com> --- include/linux/refcount.h | 19 ++++++++ lib/refcount.c | 124 ++++++++++++++++++++++++++++++++++++++++++----- 2 files changed, 130 insertions(+), 13 deletions(-)