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Subject[PATCH 17/19] ptrace: don't let PTRACE_SETSIGINFO override __SI_TRAP siginfo
Date
__SI_TRAP siginfo is special in the operation of ptrace.  It reports
group stop related information and will also interact with
notification retraps. Don't let userland mess with it.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/ptrace.c | 31 ++++++++++++++++++++++---------
1 files changed, 22 insertions(+), 9 deletions(-)
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index a205c98..a9b3c67 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -610,16 +610,29 @@ out_unlock:
static int ptrace_setsiginfo(struct task_struct *child, const siginfo_t *info)
{
unsigned long flags;
- int error = -ESRCH;
+ int error;

- if (lock_task_sighand(child, &flags)) {
- error = -EINVAL;
- if (likely(child->last_siginfo != NULL)) {
- *child->last_siginfo = *info;
- error = 0;
- }
- unlock_task_sighand(child, &flags);
- }
+ if (!lock_task_sighand(child, &flags))
+ return -ESRCH;
+
+ error = -EINVAL;
+ if (unlikely(!child->last_siginfo))
+ goto out_unlock;
+
+ /*
+ * If seized, __SI_TRAP siginfo is used to communicate information
+ * regarding traps and contains dynamic information generated on
+ * GETSIGINFO. Don't let userland override or fake it.
+ */
+ if ((child->ptrace & PT_SEIZED) &&
+ unlikely((child->last_siginfo->si_code & __SI_MASK) == __SI_TRAP ||
+ (info->si_code & __SI_MASK) == __SI_TRAP))
+ goto out_unlock;
+
+ *child->last_siginfo = *info;
+ error = 0;
+out_unlock:
+ unlock_task_sighand(child, &flags);
return error;
}

--
1.7.1


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