linux-kernel - Re: [RFC PATCH] coredump: fix incomplete core file created when dump

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Message-ID: <CAA3XUr0N_fcOqmSnT2Y=Dz+5uH1YN+qrJ=2-fJrQaHcnu1cQXw@mail.gmail.com>
Date:	Wed, 22 Oct 2014 16:21:49 -0700
From:	Victor Kamensky <victor.kamensky@...aro.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Alexander Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] coredump: fix incomplete core file created when
 dump_skip was used last

On 22 October 2014 09:55, Oleg Nesterov <oleg@...hat.com> wrote:
> On 10/21, Victor Kamensky wrote:
>>
>> +static int dump_write_last_byte(struct coredump_params *cprm)
>> +{
>> +     char lastbyte = 0;
>> +     struct file *file = cprm->file;
>> +
>> +     if (file->f_op->llseek && file->f_op->llseek != no_llseek) {
>> +             if (dump_interrupted() ||
>> +                 file->f_op->llseek(file, -1, SEEK_CUR) < 0)
>> +                     return 0;
>> +             if (!dump_emit(cprm, &lastbyte, 1))
>> +                     return 0;
>> +     }
>> +     return 1;
>> +}
>
> Perhaps do_truncate(cprm.file->f_path.dentry, ->f_pos) makes more sense?
>
> and unless I missed something cprm->last_op_status can be avoided, we can
> simply check f_pos != i_size_read() at the end?

Oleg, nice advise! Thanks.

So the whole fix becomes something like this:

diff --git a/fs/coredump.c b/fs/coredump.c
index a93f7e6..8c17f1d 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -664,6 +664,14 @@ void do_coredump(const siginfo_t *siginfo)
        if (!dump_interrupted()) {
                file_start_write(cprm.file);
                core_dumped = binfmt->core_dump(&cprm);
+               /*
+                * If last operation was dump_skip with llseek, we need to
+                * truncate file up to f_pos to match expected size.
+                */
+               if (!ispipe &&
+                   (cprm.file->f_pos > i_size_read(file_inode(cprm.file))))
+                       do_truncate(cprm.file->f_path.dentry,
+                                   cprm.file->f_pos, 0, cprm.file);
                file_end_write(cprm.file);
        }
        if (ispipe && core_pipe_limit)

May I use your name with Suggested-by tag?

Thanks,
Victor

> Oleg.
>
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