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[PATCH 4/4] x86/dumpstack: add recursion checking for all stacks

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in_exception_stack() has some recursion checking which makes sure the
stack trace code never traverses a given exception stack more than once.
This prevents an infinite loop if corruption somehow causes a stack's
"next stack" pointer to point to itself (directly or indirectly).

The recursion checking can be useful for other stacks in addition to the
exception stack, so extend it to work for all stacks.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
---
 arch/x86/kernel/dumpstack_32.c | 22 +++++++++++++++++++---
 arch/x86/kernel/dumpstack_64.c | 35 +++++++++++++++++++----------------
 2 files changed, 38 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 50076d4..2d65cfa 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -89,16 +89,32 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	task = task ? : current;
 
 	if (in_task_stack(stack, task, info))
-		return 0;
+		goto recursion_check;
 
 	if (task != current)
 		goto unknown;
 
 	if (in_hardirq_stack(stack, info))
-		return 0;
+		goto recursion_check;
 
 	if (in_softirq_stack(stack, info))
-		return 0;
+		goto recursion_check;
+
+	goto unknown;
+
+recursion_check:
+	/*
+	 * Make sure we don't iterate through any given stack more than once.
+	 * If it comes up a second time then there's something wrong going on:
+	 * just break out and report an unknown stack type.
+	 */
+	if (visit_mask) {
+		if (*visit_mask & (1UL << info->type))
+			goto unknown;
+		*visit_mask |= 1UL << info->type;
+	}
+
+	return 0;
 
 unknown:
 	info->type = STACK_TYPE_UNKNOWN;
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 2e708af..8cb6004 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -47,8 +47,7 @@ void stack_type_str(enum stack_type type, const char **begin, const char **end)
 	}
 }
 
-static bool in_exception_stack(unsigned long *stack, struct stack_info *info,
-			       unsigned long *visit_mask)
+static bool in_exception_stack(unsigned long *stack, struct stack_info *info)
 {
 	unsigned long *begin, *end;
 	struct pt_regs *regs;
@@ -64,16 +63,6 @@ static bool in_exception_stack(unsigned long *stack, struct stack_info *info,
 		if (stack < begin || stack >= end)
 			continue;
 
-		/*
-		 * Make sure we don't iterate through an exception stack more
-		 * than once.  If it comes up a second time then there's
-		 * something wrong going on - just break out and report an
-		 * unknown stack type.
-		 */
-		if (*visit_mask & (1U << k))
-			break;
-		*visit_mask |= 1U << k;
-
 		info->type	= STACK_TYPE_EXCEPTION + k;
 		info->begin	= begin;
 		info->end	= end;
@@ -119,16 +108,30 @@ int get_stack_info(unsigned long *stack, struct task_struct *task,
 	task = task ? : current;
 
 	if (in_task_stack(stack, task, info))
-		return 0;
+		goto recursion_check;
 
 	if (task != current)
 		goto unknown;
 
-	if (in_exception_stack(stack, info, visit_mask))
-		return 0;
+	if (in_exception_stack(stack, info))
+		goto recursion_check;
 
 	if (in_irq_stack(stack, info))
-		return 0;
+		goto recursion_check;
+
+	goto unknown;
+
+recursion_check:
+	/*
+	 * Make sure we don't iterate through any given stack more than once.
+	 * If it comes up a second time then there's something wrong going on:
+	 * just break out and report an unknown stack type.
+	 */
+	if (visit_mask) {
+		if (*visit_mask & (1UL << info->type))
+			goto unknown;
+		*visit_mask |= 1UL << info->type;
+	}
 
 	return 0;
 
-- 
2.7.4

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[PATCH 0/4] x86/dumpstack: yet more stack dump improvements Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-15 04:10 +0200
  [PATCH 4/4] x86/dumpstack: add recursion checking for all stacks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-15 04:10 +0200
    [tip:x86/asm] x86/dumpstack: Add recursion checking for all stacks tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-09-15 12:50 +0200
  [PATCH 2/4] x86/dumpstack: add get_stack_info() interface Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-15 04:10 +0200
    [tip:x86/asm] x86/dumpstack: Add get_stack_info() interface tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-09-15 12:50 +0200
  [PATCH 3/4] x86/dumpstack: support for unwinding empty irq stacks Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-15 04:10 +0200
    [tip:x86/asm] x86/dumpstack: Add support for unwinding empty IRQ  stacks tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-09-15 12:50 +0200
  [PATCH 1/4] x86/dumpstack: simplify in_exception_stack() Josh Poimboeuf <jpoimboe@redhat.com> - 2016-09-15 04:10 +0200
    [tip:x86/asm] x86/dumpstack: Simplify in_exception_stack() tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-09-15 12:50 +0200

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