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authorFrederic Weisbecker <fweisbec@gmail.com>2011-04-07 16:53:20 +0200
committerFrederic Weisbecker <fweisbec@gmail.com>2011-04-25 17:28:24 +0200
commitbf26c018490c2fce7fe9b629083b96ce0e6ad019 (patch)
treeff595f6268cb6fc675beb6accf6abb0701829443 /kernel
parentf4929bd37208540c2c6f416e9035ff1938f2dbc6 (diff)
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ptrace: Prepare to fix racy accesses on task breakpoints
When a task is traced and is in a stopped state, the tracer may execute a ptrace request to examine the tracee state and get its task struct. Right after, the tracee can be killed and thus its breakpoints released. This can happen concurrently when the tracer is in the middle of reading or modifying these breakpoints, leading to dereferencing a freed pointer. Hence, to prepare the fix, create a generic breakpoint reference holding API. When a reference on the breakpoints of a task is held, the breakpoints won't be released until the last reference is dropped. After that, no more ptrace request on the task's breakpoints can be serviced for the tracer. Reported-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Ingo Molnar <mingo@elte.hu> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Will Deacon <will.deacon@arm.com> Cc: Prasad <prasad@linux.vnet.ibm.com> Cc: Paul Mundt <lethal@linux-sh.org> Cc: v2.6.33.. <stable@kernel.org> Link: http://lkml.kernel.org/r/1302284067-7860-2-git-send-email-fweisbec@gmail.com
Diffstat (limited to 'kernel')
-rw-r--r--kernel/exit.c2
-rw-r--r--kernel/ptrace.c17
2 files changed, 18 insertions, 1 deletions
diff --git a/kernel/exit.c b/kernel/exit.c
index f5d2f63bae0b..8dd874181542 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1016,7 +1016,7 @@ NORET_TYPE void do_exit(long code)
/*
* FIXME: do that only when needed, using sched_exit tracepoint
*/
- flush_ptrace_hw_breakpoint(tsk);
+ ptrace_put_breakpoints(tsk);
exit_notify(tsk, group_dead);
#ifdef CONFIG_NUMA
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 0fc1eed28d27..dc7ab65f3b36 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -22,6 +22,7 @@
#include <linux/syscalls.h>
#include <linux/uaccess.h>
#include <linux/regset.h>
+#include <linux/hw_breakpoint.h>
/*
@@ -879,3 +880,19 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
return ret;
}
#endif /* CONFIG_COMPAT */
+
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+int ptrace_get_breakpoints(struct task_struct *tsk)
+{
+ if (atomic_inc_not_zero(&tsk->ptrace_bp_refcnt))
+ return 0;
+
+ return -1;
+}
+
+void ptrace_put_breakpoints(struct task_struct *tsk)
+{
+ if (atomic_dec_and_test(&tsk->ptrace_bp_refcnt))
+ flush_ptrace_hw_breakpoint(tsk);
+}
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */