[PATCH v3 2/3] vsprintf: print <symbol not found> if symbol not found

From: Tobin C. Harding
Date: Tue Dec 19 2017 - 16:40:00 EST

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 <me@xxxxxxxx>
lib/vsprintf.c | 9 +++++----
1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 01c3957b2de6..503402a44ffe 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -674,6 +674,7 @@ char *symbol_string(char *buf, char *end, void *ptr,
unsigned long value;
char sym[KSYM_SYMBOL_LEN];
+ int ret;

if (fmt[1] == 'R')
@@ -682,13 +683,13 @@ 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);

- return string(buf, end, sym, spec);
+ return string(buf, end, ret == -1 ? "<symbol not found>" : sym, spec);
return special_hex_number(buf, end, value, sizeof(void *));