[PATCH -next v2 04/12] pstore: Avoid duplicate call of persistent_ram_zap()

[Kees Cook]

From: Peng Wang <wangpeng15@xxxxxxxxxx>

When initialing a prz, if invalid data is found (no PERSISTENT_RAM_SIG),
the function call path looks like this:

ramoops_init_prz ->
    persistent_ram_new -> persistent_ram_post_init -> persistent_ram_zap
    persistent_ram_zap

As we can see, persistent_ram_zap() is called twice.
We can avoid this by adding an option to persistent_ram_new(), and
only call persistent_ram_zap() when it is needed.

Signed-off-by: Peng Wang <wangpeng15@xxxxxxxxxx>
[kees: minor tweak to exit path and commit log]
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/pstore/ram.c            |  4 +---
 fs/pstore/ram_core.c       | 15 +++++++++------
 include/linux/pstore_ram.h |  1 +
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index e02a9039b5ea..768759841491 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -640,7 +640,7 @@ static int ramoops_init_prz(const char *name,
 
 	label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
 	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
-				  cxt->memtype, 0, label);
+				  cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
 	if (IS_ERR(*prz)) {
 		int err = PTR_ERR(*prz);
 
@@ -649,8 +649,6 @@ static int ramoops_init_prz(const char *name,
 		return err;
 	}
 
-	persistent_ram_zap(*prz);
-
 	*paddr += sz;
 
 	return 0;
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index 12e21f789194..23ca6f2c98a0 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -489,6 +489,7 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
 				    struct persistent_ram_ecc_info *ecc_info)
 {
 	int ret;
+	bool zap = !!(prz->flags & PRZ_FLAG_ZAP_OLD);
 
 	ret = persistent_ram_init_ecc(prz, ecc_info);
 	if (ret)
@@ -498,23 +499,25 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
 
 	if (prz->buffer->sig == sig) {
 		if (buffer_size(prz) > prz->buffer_size ||
-		    buffer_start(prz) > buffer_size(prz))
+		    buffer_start(prz) > buffer_size(prz)) {
 			pr_info("found existing invalid buffer, size %zu, start %zu\n",
 				buffer_size(prz), buffer_start(prz));
-		else {
+			zap = true;
+		} else {
 			pr_debug("found existing buffer, size %zu, start %zu\n",
 				 buffer_size(prz), buffer_start(prz));
 			persistent_ram_save_old(prz);
-			return 0;
 		}
 	} else {
 		pr_debug("no valid data in buffer (sig = 0x%08x)\n",
 			 prz->buffer->sig);
+		prz->buffer->sig = sig;
+		zap = true;
 	}
 
-	/* Rewind missing or invalid memory area. */
-	prz->buffer->sig = sig;
-	persistent_ram_zap(prz);
+	/* Reset missing, invalid, or single-use memory area. */
+	if (zap)
+		persistent_ram_zap(prz);
 
 	return 0;
 }
diff --git a/include/linux/pstore_ram.h b/include/linux/pstore_ram.h
index 602d64725222..6e94980357d2 100644
--- a/include/linux/pstore_ram.h
+++ b/include/linux/pstore_ram.h
@@ -30,6 +30,7 @@
  * PRZ_FLAG_NO_LOCK is used. For all other cases, locking is required.
  */
 #define PRZ_FLAG_NO_LOCK	BIT(0)
+#define PRZ_FLAG_ZAP_OLD	BIT(1)
 
 struct persistent_ram_buffer;
 struct rs_control;
-- 
2.17.1