linux-hardening - [PATCH 4/5] pstore/ram: Set freed addresses to NULL

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Date:   Tue, 11 Oct 2022 13:01:11 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        Paramjit Oberoi <pso@...omium.org>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        Ard Biesheuvel <ardb@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH 4/5] pstore/ram: Set freed addresses to NULL

For good measure, set all the freed addresses to NULL when managing
przs.

Cc: Anton Vorontsov <anton@...msg.org>
Cc: Colin Cross <ccross@...roid.com>
Cc: Tony Luck <tony.luck@...el.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 fs/pstore/ram.c          | 13 ++++++++-----
 fs/pstore/ram_core.c     | 11 +++++++++--
 fs/pstore/ram_internal.h |  2 +-
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index f5bf360cf905..5da31565f93a 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -453,25 +453,27 @@ static void ramoops_free_przs(struct ramoops_context *cxt)
 	int i;
 
 	/* Free pmsg PRZ */
-	persistent_ram_free(cxt->mprz);
+	persistent_ram_free(&cxt->mprz);
 
 	/* Free console PRZ */
-	persistent_ram_free(cxt->cprz);
+	persistent_ram_free(&cxt->cprz);
 
 	/* Free dump PRZs */
 	if (cxt->dprzs) {
 		for (i = 0; i < cxt->max_dump_cnt; i++)
-			persistent_ram_free(cxt->dprzs[i]);
+			persistent_ram_free(&cxt->dprzs[i]);
 
 		kfree(cxt->dprzs);
+		cxt->fprzs = NULL;
 		cxt->max_dump_cnt = 0;
 	}
 
 	/* Free ftrace PRZs */
 	if (cxt->fprzs) {
 		for (i = 0; i < cxt->max_ftrace_cnt; i++)
-			persistent_ram_free(cxt->fprzs[i]);
+			persistent_ram_free(&cxt->fprzs[i]);
 		kfree(cxt->fprzs);
+		cxt->fprzs = NULL;
 		cxt->max_ftrace_cnt = 0;
 	}
 }
@@ -555,9 +557,10 @@ static int ramoops_init_przs(const char *name,
 
 			while (i > 0) {
 				i--;
-				persistent_ram_free(prz_ar[i]);
+				persistent_ram_free(&prz_ar[i]);
 			}
 			kfree(prz_ar);
+			prz_ar = NULL;
 			goto fail;
 		}
 		*paddr += zone_sz;
diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
index 9e1047f4316d..97dde525150a 100644
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -544,8 +544,14 @@ static int persistent_ram_post_init(struct persistent_ram_zone *prz, u32 sig,
 	return 0;
 }
 
-void persistent_ram_free(struct persistent_ram_zone *prz)
+void persistent_ram_free(struct persistent_ram_zone **_prz)
 {
+	struct persistent_ram_zone *prz;
+
+	if (!_prz)
+		return;
+
+	prz = *_prz;
 	if (!prz)
 		return;
 
@@ -569,6 +575,7 @@ void persistent_ram_free(struct persistent_ram_zone *prz)
 	persistent_ram_free_old(prz);
 	kfree(prz->label);
 	kfree(prz);
+	*_prz = NULL;
 }
 
 struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
@@ -605,6 +612,6 @@ struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 
 	return prz;
 err:
-	persistent_ram_free(prz);
+	persistent_ram_free(&prz);
 	return ERR_PTR(ret);
 }
diff --git a/fs/pstore/ram_internal.h b/fs/pstore/ram_internal.h
index 440ee7a35e10..5f694698351f 100644
--- a/fs/pstore/ram_internal.h
+++ b/fs/pstore/ram_internal.h
@@ -82,7 +82,7 @@ struct persistent_ram_zone {
 struct persistent_ram_zone *persistent_ram_new(phys_addr_t start, size_t size,
 			u32 sig, struct persistent_ram_ecc_info *ecc_info,
 			unsigned int memtype, u32 flags, char *label);
-void persistent_ram_free(struct persistent_ram_zone *prz);
+void persistent_ram_free(struct persistent_ram_zone **_prz);
 void persistent_ram_zap(struct persistent_ram_zone *prz);
 
 int persistent_ram_write(struct persistent_ram_zone *prz, const void *s,
-- 
2.34.1