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Re: [PATCH -tip 1/3] Pass mm->flags to binfmt core_dump for bitflag consistency
- From: Masami Hiramatsu <mhiramat at redhat dot com>
- To: Ingo Molnar <mingo at elte dot hu>
- Cc: Andrew Morton <akpm at linux-foundation dot org>, lkml <linux-kernel at vger dot kernel dot org>, systemtap <systemtap at sources dot redhat dot com>, DLE <dle-develop at lists dot sourceforge dot net>, Hidehiro Kawai <hidehiro dot kawai dot ez at hitachi dot com>, Oleg Nesterov <oleg at redhat dot com>, Roland McGrath <roland at redhat dot com>
- Date: Fri, 13 Nov 2009 18:44:53 -0500
- Subject: Re: [PATCH -tip 1/3] Pass mm->flags to binfmt core_dump for bitflag consistency
- References: <20091113225226.15079.90813.stgit@harusame> <20091113150904.56c15910.akpm@linux-foundation.org> <20091113232457.GC21666@elte.hu>
Ingo Molnar wrote:
* Andrew Morton<akpm@linux-foundation.org> wrote:
On Fri, 13 Nov 2009 17:52:27 -0500
Masami Hiramatsu<mhiramat@redhat.com> wrote:
Pass mm->flags to binfmt core_dump for bitflag consistency.
Since mm->flags bit flags is not protected by locks, it will be
changed while dumping core. This patch copies mm->flags to a
mm_flags local variable at the beginning of do_coredump() and
use it while dumping. mm_flags also includes dump_filter which
filters elf sections from core file in elf_core_dump().
So, this patch also passes mm_flags to each binfmt->core_dump().
I can kind-of guess the answer, but it would be much more reliable if
we were to hear this from yourself:
Why did you write this patch? What problem is being observed?
i'm not Masami so i'm only guessing that while writing the tracepoint a
race got noticed but that otherwise there's no big practical effect,
'just' a cleanliness problem fixed.
Right, I'd like to add a tracepoint of coredump event with
its information. And also, this patch may fix a small
dumpable inconsistency issue below code
---
1787 if (mm->core_state || !get_dumpable(mm)) { <- (1)
1788 up_write(&mm->mmap_sem);
1789 put_cred(cred);
1790 goto fail;
1791 }
1792
[...]
1798 if (get_dumpable(mm) == 2) { /* Setuid core dump mode */ <-(2)
1799 flag = O_EXCL; /* Stop rewrite attacks */
1800 cred->fsuid = 0; /* Dump root private */
1801 }
Since dumpable bits are not protected by lock, there is a
chance to change these bits between (1) and (2).
This patch copies mm->flags to a local variable and check the variable
for consistency.
Thank you,
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America), Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com