From 4617721c502b2ddaa4e324e86da4997edf738fa5 Mon Sep 17 00:00:00 2001 From: Steven Rostedt Date: Wed, 2 Sep 2026 09:55:01 -0400 Subject: ftrace: Synchronize the initialization of ftrace_ops There's some internal state that ftrace_ops needs to have set, but since it can be declared outside of the ftrace.c code, it calls ftrace_ops_init() on the ops in every global function. The issue is that if two tasks call it on the same ops at the same time it is possible to have the initialization of one corrupt the initialization of the other call. Create a ops_mutex to use to synchronize every initialization of the ftrace_ops. The mutex is taken within checking the ftrace_ops flag that states it was initializied but the flag is checked again after the mutex has been taken. Checking first outside the mutex allows it to shortcut having to take the mutex. But then the check needs to be done again after the mute is taken in case of races. Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260902095501.6b59af20@gandalf.local.home Fixes: f04f24fb7e48d ("ftrace, kprobes: Fix a deadlock on ftrace_regex_lock") Reported-by: sashiko-bot@kernel.org Close: https://lore.kernel.org/all/20260829025528.49A831F000E9@smtp.kernel.org/ Signed-off-by: Steven Rostedt --- lib/refcount.c | 186 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 186 insertions(+) create mode 100644 lib/refcount.c (limited to 'lib/refcount.c') diff --git a/lib/refcount.c b/lib/refcount.c new file mode 100644 index 000000000..a207a8f22 --- /dev/null +++ b/lib/refcount.c @@ -0,0 +1,186 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Out-of-line refcount functions. + */ + +#include +#include +#include +#include + +#define REFCOUNT_WARN(str) WARN_ONCE(1, "refcount_t: " str ".\n") + +void refcount_warn_saturate(refcount_t *r, enum refcount_saturation_type t) +{ + refcount_set(r, REFCOUNT_SATURATED); + + switch (t) { + case REFCOUNT_ADD_NOT_ZERO_OVF: + REFCOUNT_WARN("saturated; leaking memory"); + break; + case REFCOUNT_ADD_OVF: + REFCOUNT_WARN("saturated; leaking memory"); + break; + case REFCOUNT_ADD_UAF: + REFCOUNT_WARN("addition on 0; use-after-free"); + break; + case REFCOUNT_SUB_UAF: + REFCOUNT_WARN("underflow; use-after-free"); + break; + case REFCOUNT_DEC_LEAK: + REFCOUNT_WARN("decrement hit 0; leaking memory"); + break; + default: + REFCOUNT_WARN("unknown saturation event!?"); + } +} +EXPORT_SYMBOL(refcount_warn_saturate); + +/** + * 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. + * + * Like all decrement operations, it provides release memory order and provides + * a control dependency. + * + * 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) +{ + int val = 1; + + return atomic_try_cmpxchg_release(&r->refs, &val, 0); +} +EXPORT_SYMBOL(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) +{ + unsigned int new, val = atomic_read(&r->refs); + + do { + if (unlikely(val == REFCOUNT_SATURATED)) + return true; + + if (val == 1) + return false; + + new = val - 1; + if (new > val) { + WARN_ONCE(new > val, "refcount_t: underflow; use-after-free.\n"); + return true; + } + + } while (!atomic_try_cmpxchg_release(&r->refs, &val, new)); + + return true; +} +EXPORT_SYMBOL(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 REFCOUNT_SATURATED. + * + * 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) +{ + if (refcount_dec_not_one(r)) + return false; + + mutex_lock(lock); + if (!refcount_dec_and_test(r)) { + mutex_unlock(lock); + return false; + } + + return true; +} +EXPORT_SYMBOL(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 REFCOUNT_SATURATED. + * + * 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) +{ + if (refcount_dec_not_one(r)) + return false; + + spin_lock(lock); + if (!refcount_dec_and_test(r)) { + spin_unlock(lock); + return false; + } + + return true; +} +EXPORT_SYMBOL(refcount_dec_and_lock); + +/** + * refcount_dec_and_lock_irqsave - return holding spinlock with disabled + * interrupts if able to decrement refcount to 0 + * @r: the refcount + * @lock: the spinlock to be locked + * @flags: saved IRQ-flags if the is acquired + * + * Same as refcount_dec_and_lock() above except that the spinlock is acquired + * with disabled interrupts. + * + * Return: true and hold spinlock if able to decrement refcount to 0, false + * otherwise + */ +bool refcount_dec_and_lock_irqsave(refcount_t *r, spinlock_t *lock, + unsigned long *flags) +{ + if (refcount_dec_not_one(r)) + return false; + + spin_lock_irqsave(lock, *flags); + if (!refcount_dec_and_test(r)) { + spin_unlock_irqrestore(lock, *flags); + return false; + } + + return true; +} +EXPORT_SYMBOL(refcount_dec_and_lock_irqsave); -- cgit v1.3.1