From 9f339e7028e2855717af3193c938f9960ad13b38 Mon Sep 17 00:00:00 2001 From: Markus Metzger Date: Wed, 11 Feb 2009 15:10:27 +0100 Subject: x86, ptrace, mm: fix double-free on race Ptrace_detach() races with __ptrace_unlink() if the traced task is reaped while detaching. This might cause a double-free of the BTS buffer. Change the ptrace_detach() path to only do the memory accounting in ptrace_bts_detach() and leave the buffer free to ptrace_bts_untrace() which will be called from __ptrace_unlink(). The fix follows a proposal from Oleg Nesterov. Reported-by: Oleg Nesterov Signed-off-by: Markus Metzger Signed-off-by: Ingo Molnar --- arch/x86/kernel/ptrace.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) (limited to 'arch/x86/kernel') diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index 0a5df5f82fb..5a4c23d8989 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -810,12 +810,16 @@ static void ptrace_bts_untrace(struct task_struct *child) static void ptrace_bts_detach(struct task_struct *child) { - if (unlikely(child->bts)) { - ds_release_bts(child->bts); - child->bts = NULL; - - ptrace_bts_free_buffer(child); - } + /* + * Ptrace_detach() races with ptrace_untrace() in case + * the child dies and is reaped by another thread. + * + * We only do the memory accounting at this point and + * leave the buffer deallocation and the bts tracer + * release to ptrace_bts_untrace() which will be called + * later on with tasklist_lock held. + */ + release_locked_buffer(child->bts_buffer, child->bts_size); } #else static inline void ptrace_bts_fork(struct task_struct *tsk) {} -- cgit v1.2.3