linux-kernel - [PATCH v2] vsprintf: protect kernel from panic due to non-canonical pointer dereference

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Date:   Mon, 17 Oct 2022 13:44:47 -0600
From:   Jane Chu <jane.chu@...cle.com>
To:     pmladek@...e.com, rostedt@...dmis.org, senozhatsky@...omium.org,
        andriy.shevchenko@...ux.intel.com, linux@...musvillemoes.dk,
        linux-kernel@...r.kernel.org
Cc:     jane.chu@...cle.com
Subject: [PATCH v2] vsprintf: protect kernel from panic due to non-canonical pointer dereference

While debugging a separate issue, it was found that an invalid string
pointer could very well contain a non-canical address, such as
0x7665645f63616465. In that case, this line of defense isn't enough
to protect the kernel from crashing due to general protection fault

	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
                return "(efault)";

So run one more round of check via kern_addr_valid(). On architectures
that provide meaningful implementation, this line of check effectively
catches non-canonical pointers, etc.

Signed-off-by: Jane Chu <jane.chu@...cle.com>
---
 lib/vsprintf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index c414a8d9f1ea..b38c12ef1e45 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -698,6 +698,9 @@ static const char *check_pointer_msg(const void *ptr)
 	if ((unsigned long)ptr < PAGE_SIZE || IS_ERR_VALUE(ptr))
 		return "(efault)";

+	if (!kern_addr_valid((unsigned long)ptr))
+		return "(efault)";
+
 	return NULL;
 }

-- 
2.18.4