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

[Geert Uytterhoeven <geert+renesas@glider.be>]

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+renesas@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