From: Peter Zijlstra <peterz@infradead.org>
To: will@kernel.org, boqun.feng@gmail.com
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
peterz@infradead.org, mark.rutland@arm.com, elver@google.com,
keescook@chromium.org, hch@infradead.org,
torvalds@linux-foundation.org, axboe@kernel.dk
Subject: [PATCH v2 6/9] refcount: Fix refcount_dec_not_one()
Date: Fri, 10 Dec 2021 17:16:24 +0100 [thread overview]
Message-ID: <20211210162313.682094686@infradead.org> (raw)
In-Reply-To: 20211210161618.645249719@infradead.org
refcount_dec_not_one() misbehaves when racing against the other
refcount ops, notably it directly compares against REFCOUNT_SATURATED,
even though, through aforementioned races, the value might be slightly
off.
Additionally, when refcount_dec_not_one() is used to decrement zero;
which is valid, because 0 is not one, then it behaves differently from
the other refcount_dec*() functions in that it doesn't call
refcount_warn_saturate().
In order to allow some fuzz around the corners of the positive range,
test for saturation slightly differently.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
lib/refcount.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/lib/refcount.c
+++ b/lib/refcount.c
@@ -81,7 +81,8 @@ bool refcount_dec_not_one(refcount_t *r)
unsigned int new, val = atomic_read(&r->refs);
do {
- if (unlikely(val == REFCOUNT_SATURATED))
+ /* SAT+SAT/2 < val < SAT-SAT/2 */
+ if (unlikely(val - (REFCOUNT_SATURATED + REFCOUNT_SATURATED/2) < -REFCOUNT_SATURATED))
return true;
if (val == 1)
@@ -89,7 +90,7 @@ bool refcount_dec_not_one(refcount_t *r)
new = val - 1;
if (new > val) {
- WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n");
+ refcount_warn_saturate(r, REFCOUNT_SUB_UAF);
return true;
}
next prev parent reply other threads:[~2021-12-10 16:27 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-10 16:16 [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-10 16:16 ` [PATCH v2 1/9] atomic: Prepare scripts for macro ops Peter Zijlstra
2021-12-10 17:27 ` Mark Rutland
2021-12-10 17:43 ` Marco Elver
2021-12-10 16:16 ` [PATCH v2 2/9] atomic: Add xchg.tbl Peter Zijlstra
2021-12-13 9:50 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 3/9] atomic: Introduce atomic_{inc,dec,dec_and_test}_overflow() Peter Zijlstra
2021-12-13 10:06 ` Mark Rutland
2021-12-13 10:57 ` Peter Zijlstra
2021-12-13 10:59 ` Peter Zijlstra
2021-12-13 11:09 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 4/9] refcount: Use atomic_*_overflow() Peter Zijlstra
2021-12-13 10:35 ` Mark Rutland
2021-12-10 16:16 ` [PATCH v2 5/9] atomic,x86: Implement atomic_dec_and_test_overflow() Peter Zijlstra
2021-12-13 11:04 ` Mark Rutland
2021-12-10 16:16 ` Peter Zijlstra [this message]
2021-12-10 16:16 ` [PATCH v2 7/9] refcount: Prepare for atomic_*_overflow() offsets Peter Zijlstra
2021-12-10 16:16 ` [PATCH v2 8/9] atomic,x86: Alternative atomic_*_overflow() scheme Peter Zijlstra
2021-12-10 16:53 ` Linus Torvalds
2021-12-10 17:27 ` Linus Torvalds
2021-12-17 3:38 ` Herbert Xu
2021-12-13 16:43 ` Peter Zijlstra
2021-12-13 17:29 ` Marco Elver
2021-12-13 18:11 ` Linus Torvalds
2021-12-13 18:18 ` Marco Elver
2021-12-13 18:24 ` Linus Torvalds
2021-12-13 19:35 ` Marco Elver
2021-12-13 18:21 ` Linus Torvalds
2021-12-10 16:16 ` [PATCH v2 9/9] refcount: Optimize __refcount_add_not_zero(.i=1) Peter Zijlstra
2021-12-10 19:37 ` [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-13 12:15 ` [PATCH v2 10/9] atomic: Document the atomic_{}_overflow() functions Peter Zijlstra
2021-12-13 12:20 ` [PATCH v2 0/9] refcount: Improve code-gen Peter Zijlstra
2021-12-13 14:42 ` Marco Elver
2021-12-13 16:11 ` Peter Zijlstra
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