Re: [REGRESSION] coredumps truncated after "new helper: dump_align()"

Al Viro
2013-11-17T06:19:16Z

On Sat, Nov 16, 2013 at 12:04:08AM +0000, Al Viro wrote:
> On Fri, Nov 15, 2013 at 10:34:43PM +0100, Peter Wu wrote:
>
> > Unfortunately, this patch still does not fix the issue. I rm'd the output
> > directory just to be sure, but the bug is still there. What does this commit
> > do anyway? The commit message is quite vague.
>
> Introduces a helper that used to be open-coded in a bunch of places -
> pads the coredump to given alignment. And switches those places
> to that new helper...
>
> FWIW, I haven't tried that on your config yet, but here (with the patch
> in my previous mail) I'm seeing a sane-looking coredump -
> -rw------- 1 root root 315392 Nov 15 17:48 core
> Different userland, presumably, since that static binary is 684349
> bytes long.
>
> I'll try to reproduce with your config...

... and on your config I'm seeing
Inited
Segmentation fault (core dumped)
[ 0.123351] Core size: 315392
in the log. Same size, same apparently sane coredump. Can you check what you
get on mainline + diff below (combination of dump_align() and locking fix)?

diff --git a/fs/coredump.c b/fs/coredump.c
index 62406b6..bc3fbcd 100644
--- a/fs/coredump.c
+++ b/fs/coredump.c
@@ -695,7 +695,7 @@ int dump_emit(struct coredump_params *cprm, const void *addr, int nr)
while (nr) {
if (dump_interrupted())
return 0;
- n = vfs_write(file, addr, nr, &pos);
+ n = __kernel_write(file, addr, nr, &pos);
if (n <= 0)
return 0;
file->f_pos = pos;
@@ -733,7 +733,7 @@ int dump_align(struct coredump_params *cprm, int align)
{
unsigned mod = cprm->written & (align - 1);
if (align & (align - 1))
- return -EINVAL;
- return mod ? dump_skip(cprm, align - mod) : 0;
+ return 0;
+ return mod ? dump_skip(cprm, align - mod) : 1;
}
EXPORT_SYMBOL(dump_align);