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ptrace: make PTRACE_SEIZE set ptrace options specified in 'data' parameter

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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 since v2: use (unsigned long) casts instead of (long) ones, move
PTRACE_SEIZE_DEVEL-related code to separate lines of code.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Pedro Alves <palves@redhat.com>
Reviewed-by: Oleg Nesterov <oleg@redhat.com>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Denys Vlasenko 2012-03-23 15:02:42 -07:00 committed by Linus Torvalds
parent 86b6c1f301
commit aa9147c98f
1 changed files with 21 additions and 10 deletions
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31
kernel/ptrace.c
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@ -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.