pstore/ram: Write new dumps to start of recycled zones

The ram_core.c routines treat przs as circular buffers. When writing a
new crash dump, the old buffer needs to be cleared so that the new dump
doesn't end up in the wrong place (i.e. at the end).

The solution to this problem is to reset the circular buffer state before
writing a new Oops dump.

Signed-off-by: Aleksandr Yashkin <[email protected]>
Signed-off-by: Nikolay Merinov <[email protected]>
Signed-off-by: Ariel Gilman <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Fixes: 896fc1f ("pstore/ram: Switch to persistent_ram routines")
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>

Author: Aleksandr Yashkin

fs/pstore/ram.c

@@ -407,6 +407,17 @@ static int notrace ramoops_pstore_write(struct pstore_record *record)
 
 	prz = cxt->dprzs[cxt->dump_write_cnt];
 
+	/*
+	 * Since this is a new crash dump, we need to reset the buffer in
+	 * case it still has an old dump present. Without this, the new dump
+	 * will get appended, which would seriously confuse anything trying
+	 * to check dump file contents. Specifically, ramoops_read_kmsg_hdr()
+	 * expects to find a dump 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)