path: root/kernel/irq/proc.c
diff options
authorThomas Gleixner <tglx@linutronix.de>2014-12-11 23:01:41 +0100
committerThomas Gleixner <tglx@linutronix.de>2014-12-13 13:33:07 +0100
commitc291ee622165cb2c8d4e7af63fffd499354a23be (patch)
tree40737c5d5d419d35ed386d46b77f979dd5900312 /kernel/irq/proc.c
parent3a5dc1fafb016560315fe45bb4ef8bde259dd1bc (diff)
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 <tglx@linutronix.de> Cc: stable@vger.kernel.org
Diffstat (limited to 'kernel/irq/proc.c')
1 files changed, 21 insertions, 1 deletions
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index ac1ba2f11032..9dc9bfd8a678 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -15,6 +15,23 @@
#include "internals.h"
+ * Access rules:
+ *
+ * procfs protects read/write of /proc/irq/N/ files against a
+ * concurrent free of the interrupt descriptor. remove_proc_entry()
+ * immediately prevents new read/writes to happen and waits for
+ * already running read/write functions to complete.
+ *
+ * We remove the proc entries first and then delete the interrupt
+ * descriptor from the radix tree and free it. So it is guaranteed
+ * that irq_to_desc(N) is valid as long as the read/writes are
+ * permitted by procfs.
+ *
+ * The read from /proc/interrupts is a different problem because there
+ * is no protection. So the lookup and the access to irqdesc
+ * information must be protected by sparse_irq_lock.
+ */
static struct proc_dir_entry *root_irq_dir;
@@ -437,9 +454,10 @@ int show_interrupts(struct seq_file *p, void *v)
seq_putc(p, '\n');
+ irq_lock_sparse();
desc = irq_to_desc(i);
if (!desc)
- return 0;
+ goto outsparse;
raw_spin_lock_irqsave(&desc->lock, flags);
@@ -479,6 +497,8 @@ int show_interrupts(struct seq_file *p, void *v)
seq_putc(p, '\n');
raw_spin_unlock_irqrestore(&desc->lock, flags);
+ irq_unlock_sparse();
return 0;