[PATCH 4/5] refcount: Introduce refcount_long_t and APIs

Kees Cook
2024-05-02T22:33:47Z

Duplicate the refcount_t types and APIs gain refcount_long_t. This is
needed for larger counters that while currently very unlikely to overflow,
still want to detect and mitigate underflow.

Generate refcount-long.h via direct string replacements. Doing macros
like compat_binfmt_elf doesn't appear to work well.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
Cc: Will Deacon <will@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: Nicolas Schier <nicolas@fjasle.eu>
Cc: linux-kbuild@vger.kernel.org
---
MAINTAINERS | 2 +-
Makefile | 11 +-
include/linux/refcount-impl.h | 344 +++++++++++++++++++++++++++++++++
include/linux/refcount.h | 341 +-------------------------------
include/linux/refcount_types.h | 12 ++
lib/refcount.c | 17 +-
6 files changed, 385 insertions(+), 342 deletions(-)
create mode 100644 include/linux/refcount-impl.h

diff --git a/MAINTAINERS b/MAINTAINERS
index 7c121493f43d..2e6c8eaab194 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -3360,7 +3360,7 @@ S: Maintained
F: Documentation/atomic_*.txt
F: arch/*/include/asm/atomic*.h
F: include/*/atomic*.h
-F: include/linux/refcount.h
+F: include/linux/refcount*.h
F: scripts/atomic/

ATTO EXPRESSSAS SAS/SATA RAID SCSI DRIVER
diff --git a/Makefile b/Makefile
index 4bef6323c47d..a4bdcd34f323 100644
--- a/Makefile
+++ b/Makefile
@@ -1190,7 +1190,9 @@ PHONY += prepare archprepare

archprepare: outputmakefile archheaders archscripts scripts include/config/kernel.release \
asm-generic $(version_h) include/generated/utsrelease.h \
- include/generated/compile.h include/generated/autoconf.h remove-stale-files
+ include/generated/compile.h include/generated/autoconf.h \
+ include/generated/refcount-long.h \
+ remove-stale-files

prepare0: archprepare
$(Q)$(MAKE) $(build)=scripts/mod
@@ -1262,6 +1264,13 @@ filechk_compile.h = $(srctree)/scripts/mkcompile_h \
include/generated/compile.h: FORCE
$(call filechk,compile.h)

+include/generated/refcount-long.h: $(srctree)/include/linux/refcount-impl.h
+ $(Q)$(PERL) -pe 's/\b(atomic|(__)?refcount)_/\1_long_/g; \
+ s/ATOMIC_/ATOMIC_LONG_/g; \
+ s/(REFCOUNT)_(IMPL|INIT|MAX|SAT)/\1_LONG_\2/g; \
+ s/\b(U?)INT_/\1LONG_/g; \
+ s/\bint\b/long/g;' $< >$@
+
PHONY += headerdep
headerdep:
$(Q)find $(srctree)/include/ -name '*.h' | xargs --max-args 1 \
diff --git a/include/linux/refcount-impl.h b/include/linux/refcount-impl.h
new file mode 100644
index 000000000000..f5c73a0f46a4
--- /dev/null
+++ b/include/linux/refcount-impl.h
@@ -0,0 +1,344 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Variant of atomic_t specialized for reference counts.
+ *
+ * The interface matches the atomic_t interface (to aid in porting) but only
+ * provides the few functions one should use for reference counting.
+ *
+ * Saturation semantics
+ * ====================
+ *
+ * refcount_t differs from atomic_t in that the counter saturates at
+ * REFCOUNT_SATURATED and will not move once there. This avoids wrapping the
+ * counter and causing 'spurious' use-after-free issues. In order to avoid the
+ * cost associated with introducing cmpxchg() loops into all of the saturating
+ * operations, we temporarily allow the counter to take on an unchecked value
+ * and then explicitly set it to REFCOUNT_SATURATED on detecting that underflow
+ * or overflow has occurred. Although this is racy when multiple threads
+ * access the refcount concurrently, by placing REFCOUNT_SATURATED roughly
+ * equidistant from 0 and INT_MAX we minimise the scope for error:
+ *
+ * INT_MAX REFCOUNT_SATURATED UINT_MAX
+ * 0 (0x7fff_ffff) (0xc000_0000) (0xffff_ffff)
+ * +--------------------------------+----------------+----------------+
+ * <---------- bad value! ---------->
+ *
+ * (in a signed view of the world, the "bad value" range corresponds to
+ * a negative counter value).
+ *
+ * As an example, consider a refcount_inc() operation that causes the counter
+ * to overflow:
+ *
+ * int old = atomic_fetch_add_relaxed(r);
+ * // old is INT_MAX, refcount now INT_MIN (0x8000_0000)
+ * if (old < 0)
+ * atomic_set(r, REFCOUNT_SATURATED);
+ *
+ * If another thread also performs a refcount_inc() operation between the two
+ * atomic operations, then the count will continue to edge closer to 0. If it
+ * reaches a value of 1 before /any/ of the threads reset it to the saturated
+ * value, then a concurrent refcount_dec_and_test() may erroneously free the
+ * underlying object.
+ * Linux limits the maximum number of tasks to PID_MAX_LIMIT, which is currently
+ * 0x400000 (and can't easily be raised in the future beyond FUTEX_TID_MASK).
+ * With the current PID limit, if no batched refcounting operations are used and
+ * the attacker can't repeatedly trigger kernel oopses in the middle of refcount
+ * operations, this makes it impossible for a saturated refcount to leave the
+ * saturation range, even if it is possible for multiple uses of the same
+ * refcount to nest in the context of a single task:
+ *
+ * (UINT_MAX+1-REFCOUNT_SATURATED) / PID_MAX_LIMIT =
+ * 0x40000000 / 0x400000 = 0x100 = 256
+ *
+ * If hundreds of references are added/removed with a single refcounting
+ * operation, it may potentially be possible to leave the saturation range; but
+ * given the precise timing details involved with the round-robin scheduling of
+ * each thread manipulating the refcount and the need to hit the race multiple
+ * times in succession, there doesn't appear to be a practical avenue of attack
+ * even if using refcount_add() operations with larger increments.
+ *
+ * Memory ordering
+ * ===============
+ *
+ * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
+ * and provide only what is strictly required for refcounts.
+ *
+ * The increments are fully relaxed; these will not provide ordering. The
+ * rationale is that whatever is used to obtain the object we're increasing the
+ * reference count on will provide the ordering. For locked data structures,
+ * its the lock acquire, for RCU/lockless data structures its the dependent
+ * load.
+ *
+ * Do note that inc_not_zero() provides a control dependency which will order
+ * future stores against the inc, this ensures we'll never modify the object
+ * if we did not in fact acquire a reference.
+ *
+ * The decrements will provide release order, such that all the prior loads and
+ * stores will be issued before, it also provides a control dependency, which
+ * will order us against the subsequent free().
+ *
+ * The control dependency is against the load of the cmpxchg (ll/sc) that
+ * succeeded. This means the stores aren't fully ordered, but this is fine
+ * because the 1->0 transition indicates no concurrency.
+ *
+ * Note that the allocator is responsible for ordering things between free()
+ * and alloc().
+ *
+ * The decrements dec_and_test() and sub_and_test() also provide acquire
+ * ordering on success.
+ *
+ */
+#ifndef _LINUX_REFCOUNT_IMPL_H
+#define _LINUX_REFCOUNT_IMPL_H
+
+#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
+#define REFCOUNT_MAX INT_MAX
+#define REFCOUNT_SATURATED (INT_MIN / 2)
+
+void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t);
+
+/**
+ * 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, 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);
+}
+
+static inline __must_check __signed_wrap
+bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
+{
+ int old = refcount_read(r);
+
+ do {
+ if (!old)
+ break;
+ } while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));
+
+ if (oldp)
+ *oldp = old;
+
+ if (unlikely(old < 0 || old + i < 0))
+ refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
+
+ return old;
+}
+
+/**
+ * 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 REFCOUNT_SATURATED 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
+ */
+static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
+{
+ return __refcount_add_not_zero(i, r, NULL);
+}
+
+static inline __signed_wrap
+void __refcount_add(int i, refcount_t *r, int *oldp)
+{
+ int old = atomic_fetch_add_relaxed(i, &r->refs);
+
+ if (oldp)
+ *oldp = old;
+
+ if (unlikely(!old))
+ refcount_warn_saturate(r, REFCOUNT_ADD_UAF);
+ else if (unlikely(old < 0 || old + i < 0))
+ refcount_warn_saturate(r, REFCOUNT_ADD_OVF);
+}
+
+/**
+ * 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 REFCOUNT_SATURATED 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.
+ */
+static inline void refcount_add(int i, refcount_t *r)
+{
+ __refcount_add(i, r, NULL);
+}
+
+static inline __must_check bool __refcount_inc_not_zero(refcount_t *r, int *oldp)
+{
+ return __refcount_add_not_zero(1, r, oldp);
+}
+
+/**
+ * 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 REFCOUNT_SATURATED
+ * 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
+ */
+static inline __must_check bool refcount_inc_not_zero(refcount_t *r)
+{
+ return __refcount_inc_not_zero(r, NULL);
+}
+
+static inline void __refcount_inc(refcount_t *r, int *oldp)
+{
+ __refcount_add(1, r, oldp);
+}
+
+/**
+ * refcount_inc - increment a refcount
+ * @r: the refcount to increment
+ *
+ * Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
+ *
+ * Provides no memory ordering, it is assumed the caller already has a
+ * reference on the object.
+ *
+ * Will WARN if the refcount is 0, as this represents a possible use-after-free
+ * condition.
+ */
+static inline void refcount_inc(refcount_t *r)
+{
+ __refcount_inc(r, NULL);
+}
+
+static inline __must_check __signed_wrap
+bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp)
+{
+ int old = atomic_fetch_sub_release(i, &r->refs);
+
+ if (oldp)
+ *oldp = old;
+
+ if (old == i) {
+ smp_acquire__after_ctrl_dep();
+ return true;
+ }
+
+ if (unlikely(old < 0 || old - i < 0))
+ refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
+
+ return false;
+}
+
+/**
+ * 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 REFCOUNT_SATURATED.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before, and provides an acquire ordering on success such that free()
+ * must come after.
+ *
+ * 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
+ */
+static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)
+{
+ return __refcount_sub_and_test(i, r, NULL);
+}
+
+static inline __must_check bool __refcount_dec_and_test(refcount_t *r, int *oldp)
+{
+ return __refcount_sub_and_test(1, r, oldp);
+}
+
+/**
+ * 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 REFCOUNT_SATURATED.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before, and provides an acquire ordering on success such that free()
+ * must come after.
+ *
+ * Return: true if the resulting refcount is 0, false otherwise
+ */
+static inline __must_check bool refcount_dec_and_test(refcount_t *r)
+{
+ return __refcount_dec_and_test(r, NULL);
+}
+
+static inline void __refcount_dec(refcount_t *r, int *oldp)
+{
+ int old = atomic_fetch_sub_release(1, &r->refs);
+
+ if (oldp)
+ *oldp = old;
+
+ if (unlikely(old <= 1))
+ refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);
+}
+
+/**
+ * refcount_dec - decrement a refcount
+ * @r: the refcount
+ *
+ * Similar to atomic_dec(), it will WARN on underflow and fail to decrement
+ * when saturated at REFCOUNT_SATURATED.
+ *
+ * Provides release memory ordering, such that prior loads and stores are done
+ * before.
+ */
+static inline void refcount_dec(refcount_t *r)
+{
+ __refcount_dec(r, NULL);
+}
+
+extern __must_check bool refcount_dec_if_one(refcount_t *r);
+extern __must_check bool refcount_dec_not_one(refcount_t *r);
+extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) __cond_acquires(lock);
+extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(lock);
+extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
+ spinlock_t *lock,
+ unsigned long *flags) __cond_acquires(lock);
+
+#endif /* _LINUX_REFCOUNT_IMPL_H */
diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index 59b3b752394d..a744f814374f 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -1,94 +1,4 @@
/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Variant of atomic_t specialized for reference counts.
- *
- * The interface matches the atomic_t interface (to aid in porting) but only
- * provides the few functions one should use for reference counting.
- *
- * Saturation semantics
- * ====================
- *
- * refcount_t differs from atomic_t in that the counter saturates at
- * REFCOUNT_SATURATED and will not move once there. This avoids wrapping the
- * counter and causing 'spurious' use-after-free issues. In order to avoid the
- * cost associated with introducing cmpxchg() loops into all of the saturating
- * operations, we temporarily allow the counter to take on an unchecked value
- * and then explicitly set it to REFCOUNT_SATURATED on detecting that underflow
- * or overflow has occurred. Although this is racy when multiple threads
- * access the refcount concurrently, by placing REFCOUNT_SATURATED roughly
- * equidistant from 0 and INT_MAX we minimise the scope for error:
- *
- * INT_MAX REFCOUNT_SATURATED UINT_MAX
- * 0 (0x7fff_ffff) (0xc000_0000) (0xffff_ffff)
- * +--------------------------------+----------------+----------------+
- * <---------- bad value! ---------->
- *
- * (in a signed view of the world, the "bad value" range corresponds to
- * a negative counter value).
- *
- * As an example, consider a refcount_inc() operation that causes the counter
- * to overflow:
- *
- * int old = atomic_fetch_add_relaxed(r);
- * // old is INT_MAX, refcount now INT_MIN (0x8000_0000)
- * if (old < 0)
- * atomic_set(r, REFCOUNT_SATURATED);
- *
- * If another thread also performs a refcount_inc() operation between the two
- * atomic operations, then the count will continue to edge closer to 0. If it
- * reaches a value of 1 before /any/ of the threads reset it to the saturated
- * value, then a concurrent refcount_dec_and_test() may erroneously free the
- * underlying object.
- * Linux limits the maximum number of tasks to PID_MAX_LIMIT, which is currently
- * 0x400000 (and can't easily be raised in the future beyond FUTEX_TID_MASK).
- * With the current PID limit, if no batched refcounting operations are used and
- * the attacker can't repeatedly trigger kernel oopses in the middle of refcount
- * operations, this makes it impossible for a saturated refcount to leave the
- * saturation range, even if it is possible for multiple uses of the same
- * refcount to nest in the context of a single task:
- *
- * (UINT_MAX+1-REFCOUNT_SATURATED) / PID_MAX_LIMIT =
- * 0x40000000 / 0x400000 = 0x100 = 256
- *
- * If hundreds of references are added/removed with a single refcounting
- * operation, it may potentially be possible to leave the saturation range; but
- * given the precise timing details involved with the round-robin scheduling of
- * each thread manipulating the refcount and the need to hit the race multiple
- * times in succession, there doesn't appear to be a practical avenue of attack
- * even if using refcount_add() operations with larger increments.
- *
- * Memory ordering
- * ===============
- *
- * Memory ordering rules are slightly relaxed wrt regular atomic_t functions
- * and provide only what is strictly required for refcounts.
- *
- * The increments are fully relaxed; these will not provide ordering. The
- * rationale is that whatever is used to obtain the object we're increasing the
- * reference count on will provide the ordering. For locked data structures,
- * its the lock acquire, for RCU/lockless data structures its the dependent
- * load.
- *
- * Do note that inc_not_zero() provides a control dependency which will order
- * future stores against the inc, this ensures we'll never modify the object
- * if we did not in fact acquire a reference.
- *
- * The decrements will provide release order, such that all the prior loads and
- * stores will be issued before, it also provides a control dependency, which
- * will order us against the subsequent free().
- *
- * The control dependency is against the load of the cmpxchg (ll/sc) that
- * succeeded. This means the stores aren't fully ordered, but this is fine
- * because the 1->0 transition indicates no concurrency.
- *
- * Note that the allocator is responsible for ordering things between free()
- * and alloc().
- *
- * The decrements dec_and_test() and sub_and_test() also provide acquire
- * ordering on success.
- *
- */
-
#ifndef _LINUX_REFCOUNT_H
#define _LINUX_REFCOUNT_H

@@ -101,10 +11,6 @@

struct mutex;

-#define REFCOUNT_INIT(n) { .refs = ATOMIC_INIT(n), }
-#define REFCOUNT_MAX INT_MAX
-#define REFCOUNT_SATURATED (INT_MIN / 2)
-
enum refcount_saturation_type {
REFCOUNT_ADD_NOT_ZERO_OVF,
REFCOUNT_ADD_OVF,
@@ -113,249 +19,10 @@ enum refcount_saturation_type {
REFCOUNT_DEC_LEAK,
};

-void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t);
-
-/**
- * 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, 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);
-}
-
-static inline __must_check __signed_wrap
-bool __refcount_add_not_zero(int i, refcount_t *r, int *oldp)
-{
- int old = refcount_read(r);
-
- do {
- if (!old)
- break;
- } while (!atomic_try_cmpxchg_relaxed(&r->refs, &old, old + i));
-
- if (oldp)
- *oldp = old;
-
- if (unlikely(old < 0 || old + i < 0))
- refcount_warn_saturate(r, REFCOUNT_ADD_NOT_ZERO_OVF);
-
- return old;
-}
-
-/**
- * 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 REFCOUNT_SATURATED 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
- */
-static inline __must_check bool refcount_add_not_zero(int i, refcount_t *r)
-{
- return __refcount_add_not_zero(i, r, NULL);
-}
-
-static inline __signed_wrap
-void __refcount_add(int i, refcount_t *r, int *oldp)
-{
- int old = atomic_fetch_add_relaxed(i, &r->refs);
-
- if (oldp)
- *oldp = old;
-
- if (unlikely(!old))
- refcount_warn_saturate(r, REFCOUNT_ADD_UAF);
- else if (unlikely(old < 0 || old + i < 0))
- refcount_warn_saturate(r, REFCOUNT_ADD_OVF);
-}
-
-/**
- * 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 REFCOUNT_SATURATED 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.
- */
-static inline void refcount_add(int i, refcount_t *r)
-{
- __refcount_add(i, r, NULL);
-}
-
-static inline __must_check bool __refcount_inc_not_zero(refcount_t *r, int *oldp)
-{
- return __refcount_add_not_zero(1, r, oldp);
-}
-
-/**
- * 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 REFCOUNT_SATURATED
- * 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
- */
-static inline __must_check bool refcount_inc_not_zero(refcount_t *r)
-{
- return __refcount_inc_not_zero(r, NULL);
-}
-
-static inline void __refcount_inc(refcount_t *r, int *oldp)
-{
- __refcount_add(1, r, oldp);
-}
-
-/**
- * refcount_inc - increment a refcount
- * @r: the refcount to increment
- *
- * Similar to atomic_inc(), but will saturate at REFCOUNT_SATURATED and WARN.
- *
- * Provides no memory ordering, it is assumed the caller already has a
- * reference on the object.
- *
- * Will WARN if the refcount is 0, as this represents a possible use-after-free
- * condition.
- */
-static inline void refcount_inc(refcount_t *r)
-{
- __refcount_inc(r, NULL);
-}
-
-static inline __must_check __signed_wrap
-bool __refcount_sub_and_test(int i, refcount_t *r, int *oldp)
-{
- int old = atomic_fetch_sub_release(i, &r->refs);
-
- if (oldp)
- *oldp = old;
-
- if (old == i) {
- smp_acquire__after_ctrl_dep();
- return true;
- }
-
- if (unlikely(old < 0 || old - i < 0))
- refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
-
- return false;
-}
-
-/**
- * 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 REFCOUNT_SATURATED.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before, and provides an acquire ordering on success such that free()
- * must come after.
- *
- * 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
- */
-static inline __must_check bool refcount_sub_and_test(int i, refcount_t *r)
-{
- return __refcount_sub_and_test(i, r, NULL);
-}
-
-static inline __must_check bool __refcount_dec_and_test(refcount_t *r, int *oldp)
-{
- return __refcount_sub_and_test(1, r, oldp);
-}
-
-/**
- * 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 REFCOUNT_SATURATED.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before, and provides an acquire ordering on success such that free()
- * must come after.
- *
- * Return: true if the resulting refcount is 0, false otherwise
- */
-static inline __must_check bool refcount_dec_and_test(refcount_t *r)
-{
- return __refcount_dec_and_test(r, NULL);
-}
-
-static inline void __refcount_dec(refcount_t *r, int *oldp)
-{
- int old = atomic_fetch_sub_release(1, &r->refs);
-
- if (oldp)
- *oldp = old;
-
- if (unlikely(old <= 1))
- refcount_warn_saturate(r, REFCOUNT_DEC_LEAK);
-}
+/* Make the generation of refcount_long_t easier. */
+#define refcount_long_saturation_type refcount_saturation_type

-/**
- * refcount_dec - decrement a refcount
- * @r: the refcount
- *
- * Similar to atomic_dec(), it will WARN on underflow and fail to decrement
- * when saturated at REFCOUNT_SATURATED.
- *
- * Provides release memory ordering, such that prior loads and stores are done
- * before.
- */
-static inline void refcount_dec(refcount_t *r)
-{
- __refcount_dec(r, NULL);
-}
+#include <linux/refcount-impl.h>
+#include <generated/refcount-long.h>

-extern __must_check bool refcount_dec_if_one(refcount_t *r);
-extern __must_check bool refcount_dec_not_one(refcount_t *r);
-extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) __cond_acquires(lock);
-extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(lock);
-extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
- spinlock_t *lock,
- unsigned long *flags) __cond_acquires(lock);
#endif /* _LINUX_REFCOUNT_H */
diff --git a/include/linux/refcount_types.h b/include/linux/refcount_types.h
index 162004f06edf..6ea02d6a9623 100644
--- a/include/linux/refcount_types.h
+++ b/include/linux/refcount_types.h
@@ -16,4 +16,16 @@ typedef struct refcount_struct {
atomic_t refs;
} refcount_t;

+/**
+ * typedef refcount_long_t - variant of atomic64_t specialized for reference counts
+ * @refs: atomic_long_t counter field
+ *
+ * The counter saturates at REFCOUNT_LONG_SATURATED and will not move once
+ * there. This avoids wrapping the counter and causing 'spurious'
+ * use-after-free bugs.
+ */
+typedef struct refcount_long_struct {
+ atomic_long_t refs;
+} refcount_long_t;
+
#endif /* _LINUX_REFCOUNT_TYPES_H */
diff --git a/lib/refcount.c b/lib/refcount.c
index a207a8f22b3c..201304b7d7a5 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -10,10 +10,8 @@

#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n")

-void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
+static void refcount_report_saturation(enum refcount_saturation_type t)
{
- refcount_set(r, REFCOUNT_SATURATED);
-
switch (t) {
case REFCOUNT_ADD_NOT_ZERO_OVF:
REFCOUNT_WARN("saturated; leaking memory");
@@ -34,8 +32,21 @@ void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
REFCOUNT_WARN("unknown saturation event!?");
}
}
+
+void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t)
+{
+ refcount_set(r, REFCOUNT_SATURATED);
+ refcount_report_saturation(t);
+}
EXPORT_SYMBOL(refcount_warn_saturate);

+void refcount_long_warn_saturate(refcount_long_t *r, enum refcount_saturation_type t)
+{
+ refcount_long_set(r, REFCOUNT_LONG_SATURATED);
+ refcount_report_saturation(t);
+}
+EXPORT_SYMBOL(refcount_long_warn_saturate);
+
/**
* refcount_dec_if_one - decrement a refcount if it is 1
* @r: the refcount
--
2.34.1