linux-kernel - [PATCH 5.4 39/78] pstore/ram: Regularize prz label allocation lifetime

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Date:   Tue, 14 Jan 2020 11:01:13 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Cengiz Can <cengiz@...nel.wtf>,
        Kees Cook <keescook@...omium.org>
Subject: [PATCH 5.4 39/78] pstore/ram: Regularize prz label allocation lifetime

From: Kees Cook <keescook@...omium.org>

commit e163fdb3f7f8c62dccf194f3f37a7bcb3c333aa8 upstream.

In my attempt to fix a memory leak, I introduced a double-free in the
pstore error path. Instead of trying to manage the allocation lifetime
between persistent_ram_new() and its callers, adjust the logic so
persistent_ram_new() always takes a kstrdup() copy, and leaves the
caller's allocation lifetime up to the caller. Therefore callers are
_always_ responsible for freeing their label. Before, it only needed
freeing when the prz itself failed to allocate, and not in any of the
other prz failure cases, which callers would have no visibility into,
which is the root design problem that lead to both the leak and now
double-free bugs.

Reported-by: Cengiz Can <cengiz@...nel.wtf>
Link: https://lore.kernel.org/lkml/d4ec59002ede4aaf9928c7f7526da87c@kernel.wtf
Fixes: 8df955a32a73 ("pstore/ram: Fix error-path memory leak in persistent_ram_new() callers")
Cc: stable@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 fs/pstore/ram.c      |    4 ++--
 fs/pstore/ram_core.c |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -583,12 +583,12 @@ static int ramoops_init_przs(const char
 		prz_ar[i] = persistent_ram_new(*paddr, zone_sz, sig,
 					       &cxt->ecc_info,
 					       cxt->memtype, flags, label);
+		kfree(label);
 		if (IS_ERR(prz_ar[i])) {
 			err = PTR_ERR(prz_ar[i]);
 			dev_err(dev, "failed to request %s mem region (0x%zx@...llx): %d\n",
 				name, record_size,
 				(unsigned long long)*paddr, err);
-			kfree(label);
 
 			while (i > 0) {
 				i--;
@@ -629,12 +629,12 @@ static int ramoops_init_prz(const char *
 	label = kasprintf(GFP_KERNEL, "ramoops:%s", name);
 	*prz = persistent_ram_new(*paddr, sz, sig, &cxt->ecc_info,
 				  cxt->memtype, PRZ_FLAG_ZAP_OLD, label);
+	kfree(label);
 	if (IS_ERR(*prz)) {
 		int err = PTR_ERR(*prz);
 
 		dev_err(dev, "failed to request %s mem region (0x%zx@...llx): %d\n",
 			name, sz, (unsigned long long)*paddr, err);
-		kfree(label);
 		return err;
 	}
 
--- a/fs/pstore/ram_core.c
+++ b/fs/pstore/ram_core.c
@@ -574,7 +574,7 @@ struct persistent_ram_zone *persistent_r
 	/* Initialize general buffer state. */
 	raw_spin_lock_init(&prz->buffer_lock);
 	prz->flags = flags;
-	prz->label = label;
+	prz->label = kstrdup(label, GFP_KERNEL);
 
 	ret = persistent_ram_buffer_map(start, size, prz, memtype);
 	if (ret)