pstore/ram: Do not treat empty buffers as valid

The ramoops backend currently calls persistent_ram_save_old() even
if a buffer is empty. While this appears to work, it is does not seem
like the right thing to do and could lead to future bugs so lets avoid
that. It also prevents misleading prints in the logs which claim the
buffer is valid.

I got something like:

	found existing buffer, size 0, start 0

When I was expecting:

	no valid data in buffer (sig = ...)

This bails out early (and reports with pr_debug()), since it's an
acceptable state.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Co-developed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index e6375439c5aca25d172c3105ecc18d053c088429..c11711c2cc83676f687942b9bfdeb748c4f7e32c 100644 (file)
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -511,6 +511,11 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
        sig ^= PERSISTENT_RAM_SIG;
 
        if (prz->buffer->sig == sig) {
+               if (buffer_size(prz) == 0) {
+                       pr_debug("found existing empty buffer\n");
+                       return 0;
+               }
+
                if (buffer_size(prz) > prz->buffer_size ||
                    buffer_start(prz) > buffer_size(prz)) {
                        pr_info("found existing invalid buffer, size %zu, start %zu\n",