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Date: Tue, 19 Dec 2017 14:28:13 +1100
From: "Tobin C. Harding" <>
Cc: "Tobin C. Harding" <>,
	Steven Rostedt <>,
	Tycho Andersen <>,
	Linus Torvalds <>,
	Kees Cook <>,
	Andrew Morton <>,
	Daniel Borkmann <>,
	Masahiro Yamada <>,
	Alexei Starovoitov <>,,
	Network Development <>
Subject: [PATCH v2 2/3] vsprintf: print <no-symbol> if symbol not found

Depends on: commit 40eee173a35e ("kallsyms: don't leak address when
symbol not found")

Currently vsprintf for specifiers %p[SsB] relies on the behaviour of
kallsyms (sprint_symbol()) and prints the actual address if a symbol is
not found. Previous patch changes this behaviour so that sprint_symbol()
returns an error if symbol not found. With this patch in place we can
print a sanitized message '<symbol not found>' instead of leaking the

Print '<symbol not found>' for printk specifier %p[sSB] if symbol look
up fails.

Signed-off-by: Tobin C. Harding <>
 lib/vsprintf.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 01c3957b2de6..820ed4fe6e6c 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -674,6 +674,8 @@ char *symbol_string(char *buf, char *end, void *ptr,
 	unsigned long value;
 	char sym[KSYM_SYMBOL_LEN];
+	const char *sym_not_found = "<symbol not found>";
+	int ret;
 	if (fmt[1] == 'R')
@@ -682,11 +684,14 @@ char *symbol_string(char *buf, char *end, void *ptr,
 	if (*fmt == 'B')
-		sprint_backtrace(sym, value);
+		ret = sprint_backtrace(sym, value);
 	else if (*fmt != 'f' && *fmt != 's')
-		sprint_symbol(sym, value);
+		ret = sprint_symbol(sym, value);
-		sprint_symbol_no_offset(sym, value);
+		ret = sprint_symbol_no_offset(sym, value);
+	if (ret == -1)
+		strcpy(sym, sym_not_found);
 	return string(buf, end, sym, spec);

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