From c291ee622165cb2c8d4e7af63fffd499354a23be Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 11 Dec 2014 23:01:41 +0100 Subject: genirq: Prevent proc race against freeing of irq descriptors Since the rework of the sparse interrupt code to actually free the unused interrupt descriptors there exists a race between the /proc interfaces to the irq subsystem and the code which frees the interrupt descriptor. CPU0 CPU1 show_interrupts() desc = irq_to_desc(X); free_desc(desc) remove_from_radix_tree(); kfree(desc); raw_spinlock_irq(&desc->lock); /proc/interrupts is the only interface which can actively corrupt kernel memory via the lock access. /proc/stat can only read from freed memory. Extremly hard to trigger, but possible. The interfaces in /proc/irq/N/ are not affected by this because the removal of the proc file is serialized in procfs against concurrent readers/writers. The removal happens before the descriptor is freed. For architectures which have CONFIG_SPARSE_IRQ=n this is a non issue as the descriptor is never freed. It's merely cleared out with the irq descriptor lock held. So any concurrent proc access will either see the old correct value or the cleared out ones. Protect the lookup and access to the irq descriptor in show_interrupts() with the sparse_irq_lock. Provide kstat_irqs_usr() which is protecting the lookup and access with sparse_irq_lock and switch /proc/stat to use it. Document the existing kstat_irqs interfaces so it's clear that the caller needs to take care about protection. The users of these interfaces are either not affected due to SPARSE_IRQ=n or already protected against removal. Fixes: 1f5a5b87f78f "genirq: Implement a sane sparse_irq allocator" Signed-off-by: Thomas Gleixner Cc: stable@vger.kernel.org --- kernel/irq/internals.h | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'kernel/irq/internals.h') diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h index 4332d766619d..df553b0af936 100644 --- a/kernel/irq/internals.h +++ b/kernel/irq/internals.h @@ -78,8 +78,12 @@ extern void unmask_threaded_irq(struct irq_desc *desc); #ifdef CONFIG_SPARSE_IRQ static inline void irq_mark_irq(unsigned int irq) { } +extern void irq_lock_sparse(void); +extern void irq_unlock_sparse(void); #else extern void irq_mark_irq(unsigned int irq); +static inline void irq_lock_sparse(void) { } +static inline void irq_unlock_sparse(void) { } #endif extern void init_kstat_irqs(struct irq_desc *desc, int node, int nr); -- cgit v1.2.3