[PATCH 3/3] lib/vsprintf: Hash printed address for netdev bits fallback

[Geert Uytterhoeven]

The handler for "%pN" falls back to printing the raw pointer value when
using a different format than the (sole supported) special format
"%pNF", potentially leaking sensitive information regarding the kernel
layout in memory.

Avoid this leak by printing the hashed address instead.
Note that there are no in-tree users of the fallback.

Fixes: ad67b74d2469d9b8 ("printk: hash addresses printed with %p")
Signed-off-by: Geert Uytterhoeven <geert+rene...@glider.be>
---
 lib/vsprintf.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 1fb36260a44289e8..a3dc15c89c217b79 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1424,7 +1424,8 @@ char *restricted_pointer(char *buf, char *end, const void 
*ptr,
 }
 
 static noinline_for_stack
-char *netdev_bits(char *buf, char *end, const void *addr, const char *fmt)
+char *netdev_bits(char *buf, char *end, const void *addr,
+                 struct printf_spec spec,  const char *fmt)
 {
        unsigned long long num;
        int size;
@@ -1435,9 +1436,7 @@ char *netdev_bits(char *buf, char *end, const void *addr, 
const char *fmt)
                size = sizeof(netdev_features_t);
                break;
        default:
-               num = (unsigned long)addr;
-               size = sizeof(unsigned long);
-               break;
+               return ptr_to_id(buf, end, addr, spec);
        }
 
        return special_hex_number(buf, end, num, size);
@@ -1952,7 +1951,7 @@ char *pointer(const char *fmt, char *buf, char *end, void 
*ptr,
                        break;
                return restricted_pointer(buf, end, ptr, spec);
        case 'N':
-               return netdev_bits(buf, end, ptr, fmt);
+               return netdev_bits(buf, end, ptr, spec, fmt);
        case 'a':
                return address_val(buf, end, ptr, fmt);
        case 'd':
-- 
2.17.1