linux-kernel - [PATCH 1/3] kallsyms: don't leak address when symbol not found

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Date:   Mon, 18 Dec 2017 10:53:30 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     kernel-hardening@...ts.openwall.com
Cc:     "Tobin C. Harding" <me@...in.cc>,
        Steven Rostedt <rostedt@...dmis.org>,
        Tycho Andersen <tycho@...ho.ws>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexei Starovoitov <ast@...nel.org>,
        linux-kernel@...r.kernel.org,
        Network Development <netdev@...r.kernel.org>
Subject: [PATCH 1/3] kallsyms: don't leak address when symbol not found

Currently if kallsyms_lookup() fails to find the symbol then the address
is printed. This potentially leaks sensitive information. Instead of
printing the address we can return an error, giving the calling code the
option to print the address or print some sanitized message.

Return error instead of printing address to argument buffer. Leave
buffer in a sane state.

Signed-off-by: Tobin C. Harding <me@...in.cc>
---
 kernel/kallsyms.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index d5fa4116688a..23b9336c1461 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -394,8 +394,10 @@ static int __sprint_symbol(char *buffer, unsigned long address,
 
 	address += symbol_offset;
 	name = kallsyms_lookup(address, &size, &offset, &modname, buffer);
-	if (!name)
-		return sprintf(buffer, "0x%lx", address - symbol_offset);
+	if (!name) {
+		buffer[0] = '\0';
+		return -1;
+	}
 
 	if (name != buffer)
 		strcpy(buffer, name);
-- 
2.7.4