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Subject[PATCH v2 3/5] ptrace: make PTRACE_SEIZE set ptrace options specified in 'data' parameter
Date
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>
---
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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