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SubjectRe: [PATCH v2 3/5] ptrace: make PTRACE_SEIZE set ptrace options specified in 'data' parameter
On 02/10, Denys Vlasenko wrote:
>
> 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 ops.
> This was probably ok (not a bug), but let's be on a safer side.
>
> Changes in v2: update ptrace_attach() call in compat_sys_ptrace() too.
>
> Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
> Acked-by: Tejun Heo <tj@kernel.org>

Reviewed-by: Oleg Nesterov <oleg@redhat.com>

> ---
> kernel/ptrace.c | 31 +++++++++++++++++++++----------
> 1 files changed, 21 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 9acd07a..4661c5b 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -231,6 +231,7 @@ 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);
> @@ -238,19 +239,29 @@ 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 & PTRACE_SEIZE_DEVEL))
> + goto out;
> + flags &= ~(unsigned long)PTRACE_SEIZE_DEVEL;
> + if (flags & ~(unsigned long)PTRACE_O_MASK)
> + goto out;
> + flags = PT_PTRACED | PT_SEIZED | (flags << PT_OPT_FLAG_SHIFT);
> + } else {
> + flags = PT_PTRACED;
> + }
>
> audit_ptrace(task);
>
> @@ -282,11 +293,11 @@ 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;
> + flags |= PT_SEIZED;
> if (ns_capable(task_user_ns(task), CAP_SYS_PTRACE))
> - task->ptrace |= PT_PTRACE_CAP;
> + flags |= PT_PTRACE_CAP;
> + task->ptrace = flags;
>
> __ptrace_link(task, current);
>
> @@ -879,7 +890,7 @@ 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.
> @@ -1022,7 +1033,7 @@ asmlinkage long compat_sys_ptrace(compat_long_t request, compat_long_t pid,
> }
>
> 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.
> --
> 1.7.7.6
>



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