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Subject[PATCHv2] refcount: always allow checked forms
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In many cases, it would be useful to be able to use the full
sanity-checked refcount helpers regardless of CONFIG_REFCOUNT_FULL, as
this would help to avoid duplicate warnings where callers try to
sanity-check refcount manipulation.

This patch refactors things such that the full refcount helpers were
always built, as refcount_${op}_checked(), such that they can be used
regardless of CONFIG_REFCOUNT_FULL. This will allow code which *always*
wants a checked refcount to opt-in, avoiding the need to duplicate the
logic for warnings.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Kees Cook <keescook@chromium.org>
Reviewed-by: David Sterba <dsterba@suse.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will.deacon@arm.com>
---
include/linux/refcount.h | 27 +++++++++++++++++-------
lib/refcount.c | 53 +++++++++++++++++++++++-------------------------
2 files changed, 45 insertions(+), 35 deletions(-)

Since v1 [1]:
* Fix refcount_inc_checked() name
* Accumulate acks

Kees, per your reply [2], I'm assuming that either you or David will end up
picking this up as part of a series usingthe checked forms.

Mark.

[1] https://lkml.kernel.org/r/20180703100102.16615-1-mark.rutland@arm.com
[2] https://lkml.kernel.org/r/CAGXu5jLATGcq_mgetUurBriCaPmBQmBwxVW7aa9fAKM2XeSjHw@mail.gmail.com

diff --git a/include/linux/refcount.h b/include/linux/refcount.h
index a685da2c4522..b505f75ccf68 100644
--- a/include/linux/refcount.h
+++ b/include/linux/refcount.h
@@ -42,17 +42,30 @@ static inline unsigned int refcount_read(const refcount_t *r)
return atomic_read(&r->refs);
}

+extern __must_check bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r);
+extern void refcount_add_checked(unsigned int i, refcount_t *r);
+
+extern __must_check bool refcount_inc_not_zero_checked(refcount_t *r);
+extern void refcount_inc_checked(refcount_t *r);
+
+extern __must_check bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r);
+
+extern __must_check bool refcount_dec_and_test_checked(refcount_t *r);
+extern void refcount_dec_checked(refcount_t *r);
+
#ifdef CONFIG_REFCOUNT_FULL
-extern __must_check bool refcount_add_not_zero(unsigned int i, refcount_t *r);
-extern void refcount_add(unsigned int i, refcount_t *r);

-extern __must_check bool refcount_inc_not_zero(refcount_t *r);
-extern void refcount_inc(refcount_t *r);
+#define refcount_add_not_zero refcount_add_not_zero_checked
+#define refcount_add refcount_add_checked
+
+#define refcount_inc_not_zero refcount_inc_not_zero_checked
+#define refcount_inc refcount_inc_checked
+
+#define refcount_sub_and_test refcount_sub_and_test_checked

-extern __must_check bool refcount_sub_and_test(unsigned int i, refcount_t *r);
+#define refcount_dec_and_test refcount_dec_and_test_checked
+#define refcount_dec refcount_dec_checked

-extern __must_check bool refcount_dec_and_test(refcount_t *r);
-extern void refcount_dec(refcount_t *r);
#else
# ifdef CONFIG_ARCH_HAS_REFCOUNT
# include <asm/refcount.h>
diff --git a/lib/refcount.c b/lib/refcount.c
index d3b81cefce91..c042e0c90462 100644
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -38,10 +38,8 @@
#include <linux/refcount.h>
#include <linux/bug.h>

-#ifdef CONFIG_REFCOUNT_FULL
-
/**
- * refcount_add_not_zero - add a value to a refcount unless it is 0
+ * refcount_add_not_zero_checked - add a value to a refcount unless it is 0
* @i: the value to add to the refcount
* @r: the refcount
*
@@ -58,7 +56,7 @@
*
* Return: false if the passed refcount is 0, true otherwise
*/
-bool refcount_add_not_zero(unsigned int i, refcount_t *r)
+bool refcount_add_not_zero_checked(unsigned int i, refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -79,10 +77,10 @@ bool refcount_add_not_zero(unsigned int i, refcount_t *r)

return true;
}
-EXPORT_SYMBOL(refcount_add_not_zero);
+EXPORT_SYMBOL(refcount_add_not_zero_checked);

/**
- * refcount_add - add a value to a refcount
+ * refcount_add_checked - add a value to a refcount
* @i: the value to add to the refcount
* @r: the refcount
*
@@ -97,14 +95,14 @@ EXPORT_SYMBOL(refcount_add_not_zero);
* 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)
+void refcount_add_checked(unsigned int i, refcount_t *r)
{
- WARN_ONCE(!refcount_add_not_zero(i, r), "refcount_t: addition on 0; use-after-free.\n");
+ WARN_ONCE(!refcount_add_not_zero_checked(i, r), "refcount_t: addition on 0; use-after-free.\n");
}
-EXPORT_SYMBOL(refcount_add);
+EXPORT_SYMBOL(refcount_add_checked);

/**
- * refcount_inc_not_zero - increment a refcount unless it is 0
+ * refcount_inc_not_zero_checked - 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.
@@ -115,7 +113,7 @@ EXPORT_SYMBOL(refcount_add);
*
* Return: true if the increment was successful, false otherwise
*/
-bool refcount_inc_not_zero(refcount_t *r)
+bool refcount_inc_not_zero_checked(refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -134,10 +132,10 @@ bool refcount_inc_not_zero(refcount_t *r)

return true;
}
-EXPORT_SYMBOL(refcount_inc_not_zero);
+EXPORT_SYMBOL(refcount_inc_not_zero_checked);

/**
- * refcount_inc - increment a refcount
+ * refcount_inc_checked - increment a refcount
* @r: the refcount to increment
*
* Similar to atomic_inc(), but will saturate at UINT_MAX and WARN.
@@ -148,14 +146,14 @@ EXPORT_SYMBOL(refcount_inc_not_zero);
* Will WARN if the refcount is 0, as this represents a possible use-after-free
* condition.
*/
-void refcount_inc(refcount_t *r)
+void refcount_inc_checked(refcount_t *r)
{
- WARN_ONCE(!refcount_inc_not_zero(r), "refcount_t: increment on 0; use-after-free.\n");
+ WARN_ONCE(!refcount_inc_not_zero_checked(r), "refcount_t: increment on 0; use-after-free.\n");
}
-EXPORT_SYMBOL(refcount_inc);
+EXPORT_SYMBOL(refcount_inc_checked);

/**
- * refcount_sub_and_test - subtract from a refcount and test if it is 0
+ * refcount_sub_and_test_checked - subtract from a refcount and test if it is 0
* @i: amount to subtract from the refcount
* @r: the refcount
*
@@ -174,7 +172,7 @@ EXPORT_SYMBOL(refcount_inc);
*
* Return: true if the resulting refcount is 0, false otherwise
*/
-bool refcount_sub_and_test(unsigned int i, refcount_t *r)
+bool refcount_sub_and_test_checked(unsigned int i, refcount_t *r)
{
unsigned int new, val = atomic_read(&r->refs);

@@ -192,10 +190,10 @@ bool refcount_sub_and_test(unsigned int i, refcount_t *r)

return !new;
}
-EXPORT_SYMBOL(refcount_sub_and_test);
+EXPORT_SYMBOL(refcount_sub_and_test_checked);

/**
- * refcount_dec_and_test - decrement a refcount and test if it is 0
+ * refcount_dec_and_test_checked - 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
@@ -207,14 +205,14 @@ EXPORT_SYMBOL(refcount_sub_and_test);
*
* Return: true if the resulting refcount is 0, false otherwise
*/
-bool refcount_dec_and_test(refcount_t *r)
+bool refcount_dec_and_test_checked(refcount_t *r)
{
- return refcount_sub_and_test(1, r);
+ return refcount_sub_and_test_checked(1, r);
}
-EXPORT_SYMBOL(refcount_dec_and_test);
+EXPORT_SYMBOL(refcount_dec_and_test_checked);

/**
- * refcount_dec - decrement a refcount
+ * refcount_dec_checked - decrement a refcount
* @r: the refcount
*
* Similar to atomic_dec(), it will WARN on underflow and fail to decrement
@@ -223,12 +221,11 @@ EXPORT_SYMBOL(refcount_dec_and_test);
* Provides release memory ordering, such that prior loads and stores are done
* before.
*/
-void refcount_dec(refcount_t *r)
+void refcount_dec_checked(refcount_t *r)
{
- WARN_ONCE(refcount_dec_and_test(r), "refcount_t: decrement hit 0; leaking memory.\n");
+ WARN_ONCE(refcount_dec_and_test_checked(r), "refcount_t: decrement hit 0; leaking memory.\n");
}
-EXPORT_SYMBOL(refcount_dec);
-#endif /* CONFIG_REFCOUNT_FULL */
+EXPORT_SYMBOL(refcount_dec_checked);

/**
* refcount_dec_if_one - decrement a refcount if it is 1
--
2.11.0
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