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SubjectRe: [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory
Date
Kawai, Hidehiro <hidehiro.kawai.ez@hitachi.com> wrote:

> Core dumping is separated two phases, one is the phase of writing
> headers, the other is the phase of writing memory segments. If the
> coredump_omit_anon_shared setting is changed between these two phases,
> a corrupted core file will be generated because the offsets written
> in headers don't match their bodies. So we need to use the same
> setting in both phases.

Hmmm... Okay.

> I think that locking makes codes complex and generates overhead.
> So I wouldn't like to use lock as far as possible. I think passing
> the flag as an extra argument is the simplest implementation to
> avoid the core file corruption.

Actually, I don't think the locking is that hard or that complex.

int do_coredump(long signr, int exit_code, struct pt_regs * regs)
{
<setup vars>

down_read(&coredump_settings_sem);

...

fail:
up_read(&coredump_settings_sem);
return retval;
}

And:

static ssize_t proc_coredump_omit_anon_shared_write(struct file *file,
const char __user *buf,
size_t count,
loff_t *ppos)
{
<setup vars>

down_write(&coredump_settings_sem);

...

out_no_task:
up_write(&coredump_settings_sem);
return ret;
}

The same could be applied to all controls that change the coredumping
variables, in particular the sysctl for core_pattern could be wrapped so as to
remove one of the reliances on lock_kernel() and the lock_kernel pair could be
removed from do_coredump().

David
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