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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Dan Carpenter <dan.carpenter@oracle.com>,
        "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Kees Cook <keescook@chromium.org>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 169/243] pstore/ram: Avoid NULL deref in ftrace merging failure path
Date:   Wed, 11 Dec 2019 16:05:31 +0100
Message-Id: <20191211150350.589883633@linuxfoundation.org>
In-Reply-To: <20191211150339.185439726@linuxfoundation.org>
References: <20191211150339.185439726@linuxfoundation.org>
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From: Kees Cook <keescook@chromium.org>

[ Upstream commit 8665569e97dd52920713b95675409648986b5b0d ]

Given corruption in the ftrace records, it might be possible to allocate
tmp_prz without assigning prz to it, but still marking it as needing to
be freed, which would cause at least a NULL dereference.

smatch warnings:
fs/pstore/ram.c:340 ramoops_pstore_read() error: we previously assumed 'prz' could be null (see line 255)

https://lists.01.org/pipermail/kbuild-all/2018-December/055528.html

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 2fbea82bbb89 ("pstore: Merge per-CPU ftrace records into one")
Cc: "Joel Fernandes (Google)" <joel@joelfernandes.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/pstore/ram.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 015d74ee31a03..631ae057ab537 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -301,6 +301,7 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 					  GFP_KERNEL);
 			if (!tmp_prz)
 				return -ENOMEM;
+			prz = tmp_prz;
 			free_prz = true;
 
 			while (cxt->ftrace_read_cnt < cxt->max_ftrace_cnt) {
@@ -323,7 +324,6 @@ static ssize_t ramoops_pstore_read(struct pstore_record *record)
 					goto out;
 			}
 			record->id = 0;
-			prz = tmp_prz;
 		}
 	}
 
-- 
2.20.1