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Commit 71434f2f authored by Oleg Nesterov's avatar Oleg Nesterov
Browse files

uprobes: Fix the racy uprobe->flags manipulation 



Multiple threads can manipulate uprobe->flags, this is obviously
unsafe. For example mmap can set UPROBE_COPY_INSN while register
tries to set UPROBE_RUN_HANDLER, the latter can also race with
can_skip_sstep() which clears UPROBE_SKIP_SSTEP.

Change this code to use bitops.

Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Acked-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
parent 4710f05f

kernel/events/uprobes.c

+14 −14
Original line number Diff line number Diff line
@@ -79,11 +79,11 @@ static struct mutex uprobes_mmap_mutex[UPROBES_HASH_SZ]; 
static atomic_t uprobe_events = ATOMIC_INIT(0);



/* Have a copy of original instruction */

#define UPROBE_COPY_INSN	0x1

#define UPROBE_COPY_INSN	0

/* Dont run handlers when first register/ last unregister in progress*/

#define UPROBE_RUN_HANDLER	0x2

#define UPROBE_RUN_HANDLER	1

/* Can skip singlestep */

#define UPROBE_SKIP_SSTEP	0x4

#define UPROBE_SKIP_SSTEP	2



struct uprobe {

	struct rb_node		rb_node;	/* node in the rb tree */
@@ -94,7 +94,7 @@ struct uprobe { 
	struct uprobe_consumer	*consumers;

	struct inode		*inode;		/* Also hold a ref to inode */

	loff_t			offset;

	int			flags;

	unsigned long		flags;

	struct arch_uprobe	arch;

};
@@ -423,7 +423,7 @@ static struct uprobe *insert_uprobe(struct uprobe *uprobe) 
	spin_unlock(&uprobes_treelock);



	/* For now assume that the instruction need not be single-stepped */

	uprobe->flags |= UPROBE_SKIP_SSTEP;

	__set_bit(UPROBE_SKIP_SSTEP, &uprobe->flags);



	return u;

}
@@ -466,7 +466,7 @@ static void handler_chain(struct uprobe *uprobe, struct pt_regs *regs) 
{

	struct uprobe_consumer *uc;



	if (!(uprobe->flags & UPROBE_RUN_HANDLER))

	if (!test_bit(UPROBE_RUN_HANDLER, &uprobe->flags))

		return;



	down_read(&uprobe->consumer_rwsem);
@@ -577,11 +577,11 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file, 
{

	int ret = 0;



	if (uprobe->flags & UPROBE_COPY_INSN)

	if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))

		return ret;



	mutex_lock(&uprobe->copy_mutex);

	if (uprobe->flags & UPROBE_COPY_INSN)

	if (test_bit(UPROBE_COPY_INSN, &uprobe->flags))

		goto out;



	ret = copy_insn(uprobe, file);
@@ -601,7 +601,7 @@ static int prepare_uprobe(struct uprobe *uprobe, struct file *file, 
			UPROBE_SWBP_INSN_SIZE > PAGE_SIZE);



	smp_wmb(); /* pairs with rmb() in find_active_uprobe() */

	uprobe->flags |= UPROBE_COPY_INSN;

	set_bit(UPROBE_COPY_INSN, &uprobe->flags);



 out:

	mutex_unlock(&uprobe->copy_mutex);
@@ -852,7 +852,7 @@ int uprobe_register(struct inode *inode, loff_t offset, struct uprobe_consumer * 
			uprobe->consumers = NULL;

			__uprobe_unregister(uprobe);

		} else {

			uprobe->flags |= UPROBE_RUN_HANDLER;

			set_bit(UPROBE_RUN_HANDLER, &uprobe->flags);

		}

	}
@@ -885,7 +885,7 @@ void uprobe_unregister(struct inode *inode, loff_t offset, struct uprobe_consume 
	if (consumer_del(uprobe, uc)) {

		if (!uprobe->consumers) {

			__uprobe_unregister(uprobe);

			uprobe->flags &= ~UPROBE_RUN_HANDLER;

			clear_bit(UPROBE_RUN_HANDLER, &uprobe->flags);

		}

	}
@@ -1346,10 +1346,10 @@ bool uprobe_deny_signal(void) 
 */

static bool can_skip_sstep(struct uprobe *uprobe, struct pt_regs *regs)

{

	if (uprobe->flags & UPROBE_SKIP_SSTEP) {

	if (test_bit(UPROBE_SKIP_SSTEP, &uprobe->flags)) {

		if (arch_uprobe_skip_sstep(&uprobe->arch, regs))

			return true;

		uprobe->flags &= ~UPROBE_SKIP_SSTEP;

		clear_bit(UPROBE_SKIP_SSTEP, &uprobe->flags);

	}

	return false;

}
@@ -1473,7 +1473,7 @@ static void handle_swbp(struct pt_regs *regs) 
	 * new and not-yet-analyzed uprobe at the same address, restart.

	 */

	smp_rmb(); /* pairs with wmb() in install_breakpoint() */

	if (unlikely(!(uprobe->flags & UPROBE_COPY_INSN)))

	if (unlikely(!test_bit(UPROBE_COPY_INSN, &uprobe->flags)))

		goto restart;



	utask = current->utask;