Messages in this thread Patch in this message | | | From | Denys Vlasenko <> | Subject | [PATCH v2] Make PTRACE_SEIZE set ptrace options specified in 'data' parameter | Date | Wed, 7 Sep 2011 23:40:31 +0200 |
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Make PTRACE_SEIZE set ptrace options specified in 'data' parameter
This can be used to close a few corner cases in strace where we get unwanted racy behavior after attach, but before we have a chance to set options (the notorious post-execve SIGTRAP comes to mind), and removes the need to track "did we set opts for this task" state in strace internals.
While we are at it:
Make it possible to extend SEIZE in the future with more functionality by passing non-zero 'addr' parameter. To that end, error out if 'addr' is non-zero. PTRACE_ATTACH did not (and still does not) have such check, and users (strace) do pass garbage there... let's avoid repeating this mistake with SEIZE.
Set all task->ptrace bits in one operation - before this change, we were adding PT_SEIZED and PT_PTRACE_CAP with task->ptrace |= BIT. This was probably ok (not a bug), but let's be on a safer side. Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
diff --git a/kernel/ptrace.c b/kernel/ptrace.c index 0316200..43aa09c 100644 --- a/kernel/ptrace.c +++ b/kernel/ptrace.c @@ -212,6 +212,7 @@ bool ptrace_may_access(struct task_struct *task, unsigned int mode) } static int ptrace_attach(struct task_struct *task, long request, + unsigned long addr, unsigned long flags) { bool seize = (request == PTRACE_SEIZE); @@ -219,19 +220,27 @@ static int ptrace_attach(struct task_struct *task, long request, /* * SEIZE will enable new ptrace behaviors which will be implemented - * gradually. SEIZE_DEVEL is used to prevent applications + * gradually. SEIZE_DEVEL bit is used to prevent applications * expecting full SEIZE behaviors trapping on kernel commits which * are still in the process of implementing them. * * Only test programs for new ptrace behaviors being implemented * should set SEIZE_DEVEL. If unset, SEIZE will fail with -EIO. * - * Once SEIZE behaviors are completely implemented, this flag and - * the following test will be removed. + * Once SEIZE behaviors are completely implemented, this flag + * will be removed. */ retval = -EIO; - if (seize && !(flags & PTRACE_SEIZE_DEVEL)) - goto out; + if (seize) { + if (addr != 0) + goto out; + if ((flags & ~(long)PTRACE_O_MASK) != PTRACE_SEIZE_DEVEL) + goto out; + flags &= ~PTRACE_SEIZE_DEVEL; + flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT); + } else { + flags = PT_PTRACED; + } audit_ptrace(task); @@ -263,11 +272,9 @@ static int ptrace_attach(struct task_struct *task, long request, if (task->ptrace) goto unlock_tasklist; - task->ptrace = PT_PTRACED; - if (seize) - task->ptrace |= PT_SEIZED; if (task_ns_capable(task, CAP_SYS_PTRACE)) - task->ptrace |= PT_PTRACE_CAP; + flags |= PT_PTRACE_CAP; + task->ptrace = flags; __ptrace_link(task, current); @@ -865,7 +872,7 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr, } if (request == PTRACE_ATTACH || request == PTRACE_SEIZE) { - ret = ptrace_attach(child, request, data); + ret = ptrace_attach(child, request, addr, data); /* * Some architectures need to do book-keeping after * a ptrace attach.
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