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

[Adam Borowski]

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 <kilob...@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