Re: [PATCH AUTOSEL 4.19 104/123] pstore/ram: Correctly calculate usable PRZ bytes

Kees Cook
2018-12-05T22:57:30Z

On Wed, Dec 5, 2018 at 1:41 AM Sasha Levin <sashal@kernel.org> wrote:
>
> From: Kees Cook <keescook@chromium.org>
>
> [ Upstream commit 89d328f637b9904b6d4c9af73c8a608b8dd4d6f8 ]
>
> The actual number of bytes stored in a PRZ is smaller than the
> bytes requested by platform data, since there is a header on each
> PRZ. Additionally, if ECC is enabled, there are trailing bytes used
> as well. Normally this mismatch doesn't matter since PRZs are circular
> buffers and the leading "overflow" bytes are just thrown away. However, in
> the case of a compressed record, this rather badly corrupts the results.
>
> This corruption was visible with "ramoops.mem_size=204800 ramoops.ecc=1".
> Any stored crashes would not be uncompressable (producing a pstorefs
> "dmesg-*.enc.z" file), and triggering errors at boot:
>
> [ 2.790759] pstore: crypto_comp_decompress failed, ret = -22!
>
> Backporting this depends on commit 70ad35db3321 ("pstore: Convert console
> write to use ->write_buf")

Please note the above. If this gets backported, this one is needed too.

-Kees

>
> Reported-by: Joel Fernandes <joel@joelfernandes.org>
> Fixes: b0aad7a99c1d ("pstore: Add compression support to pstore")
> Signed-off-by: Kees Cook <keescook@chromium.org>
> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> fs/pstore/ram.c | 15 ++++++---------
> include/linux/pstore.h | 5 ++++-
> 2 files changed, 10 insertions(+), 10 deletions(-)
>
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index f4fd2e72add4..03cd59375abe 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -806,17 +806,14 @@ static int ramoops_probe(struct platform_device *pdev)
>
> cxt->pstore.data = cxt;
> /*
> - * Console can handle any buffer size, so prefer LOG_LINE_MAX. If we
> - * have to handle dumps, we must have at least record_size buffer. And
> - * for ftrace, bufsize is irrelevant (if bufsize is 0, buf will be
> - * ZERO_SIZE_PTR).
> + * Since bufsize is only used for dmesg crash dumps, it
> + * must match the size of the dprz record (after PRZ header
> + * and ECC bytes have been accounted for).
> */
> - if (cxt->console_size)
> - cxt->pstore.bufsize = 1024; /* LOG_LINE_MAX */
> - cxt->pstore.bufsize = max(cxt->record_size, cxt->pstore.bufsize);
> - cxt->pstore.buf = kmalloc(cxt->pstore.bufsize, GFP_KERNEL);
> + cxt->pstore.bufsize = cxt->dprzs[0]->buffer_size;
> + cxt->pstore.buf = kzalloc(cxt->pstore.bufsize, GFP_KERNEL);
> if (!cxt->pstore.buf) {
> - pr_err("cannot allocate pstore buffer\n");
> + pr_err("cannot allocate pstore crash dump buffer\n");
> err = -ENOMEM;
> goto fail_clear;
> }
> diff --git a/include/linux/pstore.h b/include/linux/pstore.h
> index a15bc4d48752..30fcec375a3a 100644
> --- a/include/linux/pstore.h
> +++ b/include/linux/pstore.h
> @@ -90,7 +90,10 @@ struct pstore_record {
> *
> * @buf_lock: spinlock to serialize access to @buf
> * @buf: preallocated crash dump buffer
> - * @bufsize: size of @buf available for crash dump writes
> + * @bufsize: size of @buf available for crash dump bytes (must match
> + * smallest number of bytes available for writing to a
> + * backend entry, since compressed bytes don't take kindly
> + * to being truncated)
> *
> * @read_mutex: serializes @open, @read, @close, and @erase callbacks
> * @flags: bitfield of frontends the backend can accept writes for
> --
> 2.17.1
>

--
Kees Cook