[PATCH 1/2] vsprintf: distinguish between (null), (err) and (invalid) pointer derefs

Adam Borowski
2018-03-06T18:12:03Z

Attempting to print an object pointed to by a bad (usually ERR_PTR) pointer
is a not so surprising error. Our code handles them inconsistently:
* two places print (null) if ptr<PAGE_SIZE
* one place prints (null) if abs(ptr)<PAGE_SIZE
* one place prints (null) only if !ptr

Obviously, saying (null) for a small but non-0 value is misleading.
Thus, let's print:
* (null) for exactly 0
* (err) if last page && abs(ptr)<=MAX_ERRNO
* (invalid) otherwise

Signed-off-by: Adam Borowski <kilobyte@angband.pl>
---
lib/vsprintf.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index d7a708f82559..1c2c3cc5a321 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -47,6 +47,8 @@
#include <linux/string_helpers.h>
#include "kstrtox.h"

+#define BAD_PTR_STRING(x) (!(x) ? "(null)" : IS_ERR(x) ? "(err)" : "(invalid)")
+
/**
* simple_strtoull - convert a string to an unsigned long long
* @cp: The start of the string
@@ -588,7 +590,7 @@ char *string(char *buf, char *end, const char *s, struct printf_spec spec)
size_t lim = spec.precision;

if ((unsigned long)s < PAGE_SIZE)
- s = "(null)";
+ s = BAD_PTR_STRING(s);

while (lim--) {
char c = *s++;
@@ -1582,7 +1584,7 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
return string(buf, end, "(!OF)", spec);

if ((unsigned long)dn < PAGE_SIZE)
- return string(buf, end, "(null)", spec);
+ return string(buf, end, BAD_PTR_STRING(dn), spec);

/* simple case without anything any more format specifiers */
fmt++;
@@ -1851,12 +1853,12 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,

if (!ptr && *fmt != 'K' && *fmt != 'x') {
/*
- * Print (null) with the same width as a pointer so it makes
- * tabular output look nice.
+ * Print (null)/etc with the same width as a pointer so it
+ * makes tabular output look nice.
*/
if (spec.field_width == -1)
spec.field_width = default_width;
- return string(buf, end, "(null)", spec);
+ return string(buf, end, BAD_PTR_STRING(ptr), spec);
}

switch (*fmt) {
@@ -2575,7 +2577,7 @@ int vbin_printf(u32 *bin_buf, size_t size, const char *fmt, va_list args)

if ((unsigned long)save_str > (unsigned long)-PAGE_SIZE
|| (unsigned long)save_str < PAGE_SIZE)
- save_str = "(null)";
+ save_str = BAD_PTR_STRING(save_str);
len = strlen(save_str) + 1;
if (str + len < end)
memcpy(str, save_str, len);
--
2.16.2