Re: [PATCH] pstore/ram: fix for adding dumps to non-empty zone
From: Kees Cook
Date: Thu Jan 02 2020 - 17:05:28 EST
On Tue, Dec 31, 2019 at 10:00:34AM +0200, Nikolai Merinov wrote:
> On Dec 31, 2019, at 1:37 AM, Kees Cook keescook@xxxxxxxxxxxx wrote:
> > On Mon, Dec 23, 2019 at 06:38:16PM +0500, Nikolai Merinov wrote:
> >> From: Aleksandr Yashkin <a.yashkin@xxxxxxxxxxxxxxxxxx>
> >> The circle buffer in ramoops zones has a problem for adding a new
> >> oops dump to already an existing one.
> >> The solution to this problem is to reset the circle buffer state before
> >> writing a new oops dump.
> > Ah, I see it now. When the crashes wrap around, the header is written at
> > the end of the (possibly incompletely filled) buffer, instead of at the
> > start, since it wasn't explicitly zapped.
> Yes, you are right. We observed this issue when we got two consecutive
> reboots with a kernel panic: After the first reboot the pstore was able
> to parse the saved data, but after the second we got a part of the
> previous compressed message and the new compressed message with the
> ramoops message header at the middle of the file.
> According to our analysis the same issue can occur if we get more
> than (rampoops.mem_size/ramoops.record_size) kernel oops during work.
Yup, perfect. Thanks for confirming! I've tested the patches with this
in mind and everything seems to be working correctly.
> > Yes, this is important; thank you for tracking this down! This bug has
> > existed for a very long time. I'll try to find the right Fixes tag for
> > it...
> We would like to see this changes in the LTS kernel releases. Could you
> please point me the manual about propagation such fixes?
You don't need to do anything. :) I have already marked it for -stable,
and it'll end up there as it makes its way through the development
> > -Kees
> >> Signed-off-by: Aleksandr Yashkin <a.yashkin@xxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Nikolay Merinov <n.merinov@xxxxxxxxxxxxxxxxxx>
> >> Signed-off-by: Ariel Gilman <a.gilman@xxxxxxxxxxxxxxxxxx>
> >> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> >> index 8caff834f002..33fceadbf515 100644
> >> --- a/fs/pstore/ram.c
> >> +++ b/fs/pstore/ram.c
> >> @@ -407,6 +407,13 @@ static int notrace ramoops_pstore_write(struct
> >> pstore_record *record)
> >> prz = cxt->dprzs[cxt->dump_write_cnt];
> >> + /* Clean the buffer from old info.
> >> + * `ramoops_read_kmsg_hdr' expects to find a header in the beginning of
> >> + * buffer data, so we must to reset the buffer values, in order to
> >> + * ensure that the header will be written to the beginning of the buffer
> >> + */
> >> + persistent_ram_zap(prz);
> >> +
> >> /* Build header and append record contents. */
> >> hlen = ramoops_write_kmsg_hdr(prz, record);
> >> if (!hlen)
> >> --
> >> 2.17.1
> > --
> > Kees Cook
> Nikolai Merinov