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authorFrederic Weisbecker <fweisbec@gmail.com>2011-04-07 16:53:20 +0200
committerNicolas Pitre <nicolas.pitre@linaro.org>2011-05-16 13:31:31 -0400
commit2b2b095909d79cbc3378dc31d86dec4eb8174504 (patch)
treeb3fabed1ba5748692a256e120b777a561f503028
parent11d9d0e35ad08fe4d2a59f0ab931ca147649a4eb (diff)
downloadlinux-linaro-android-2b2b095909d79cbc3378dc31d86dec4eb8174504.tar.gz
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 (cherry picked from commit bf26c018490c2fce7fe9b629083b96ce0e6ad019)
-rw-r--r--include/linux/ptrace.h13
-rw-r--r--include/linux/sched.h3
-rw-r--r--kernel/exit.c2
-rw-r--r--kernel/ptrace.c17
4 files changed, 33 insertions, 2 deletions
diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index a1147e5dd24..9178d5cc0b0 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -189,6 +189,10 @@ static inline void ptrace_init_task(struct task_struct *child, bool ptrace)
child->ptrace = current->ptrace;
__ptrace_link(child, current->parent);
}
+
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+ atomic_set(&child->ptrace_bp_refcnt, 1);
+#endif
}
/**
@@ -350,6 +354,13 @@ extern int task_current_syscall(struct task_struct *target, long *callno,
unsigned long args[6], unsigned int maxargs,
unsigned long *sp, unsigned long *pc);
-#endif
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+extern int ptrace_get_breakpoints(struct task_struct *tsk);
+extern void ptrace_put_breakpoints(struct task_struct *tsk);
+#else
+static inline void ptrace_put_breakpoints(struct task_struct *tsk) { }
+#endif /* CONFIG_HAVE_HW_BREAKPOINT */
+
+#endif /* __KERNEL */
#endif
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 6a7dfd8d272..bfe61550866 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1531,6 +1531,9 @@ struct task_struct {
unsigned long memsw_bytes; /* uncharged mem+swap usage */
} memcg_batch;
#endif
+#ifdef CONFIG_HAVE_HW_BREAKPOINT
+ atomic_t ptrace_bp_refcnt;
+#endif
};
/* Future-safe accessor for struct task_struct's cpus_allowed. */
diff --git a/kernel/exit.c b/kernel/exit.c
index 0d9a3444614..7cdb3a6ef7d 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1019,7 +1019,7 @@ 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 e2302e40b36..254ad5b5251 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>
/*
@@ -876,3 +877,19 @@ 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 */