[PATCH v7 10/10] vsprintf: Limit the length of inlined error messages

[Petr Mladek]

The inlined error messages must be used carefully because
they need to fit into the given buffer.

Handle them using a custom wrapper that makes people aware
of the problem. Also define a reasonable hard limit to
avoid a completely insane usage.

Suggested-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Signed-off-by: Petr Mladek <pmla...@suse.com>
---
 lib/vsprintf.c | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 4e5666035b74..1f367f3a7e2b 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -612,6 +612,21 @@ static char *string_nocheck(char *buf, char *end, const 
char *s,
        return widen_string(buf, len, end, spec);
 }
 
+/* Be careful: error messages must fit into the given buffer. */
+static char *error_string(char *buf, char *end, const char *s,
+                         struct printf_spec spec)
+{
+       /*
+        * Hard limit to avoid a completely insane messages. It actually
+        * works pretty well because most error messages are in
+        * the many pointer format modifiers.
+        */
+       if (spec.precision == -1)
+               spec.precision = 2 * sizeof(void *);
+
+       return string_nocheck(buf, end, s, spec);
+}
+
 /*
  * This is not a fool-proof test. 99% of the time that this will fault is
  * due to a bad pointer, not one that crosses into bad memory. Just test
@@ -638,7 +653,7 @@ static int check_pointer(char **buf, char *end, const void 
*ptr,
 
        err_msg = check_pointer_msg(ptr);
        if (err_msg) {
-               *buf = string_nocheck(*buf, end, err_msg, spec);
+               *buf = error_string(*buf, end, err_msg, spec);
                return -EFAULT;
        }
 
@@ -741,7 +756,7 @@ static char *ptr_to_id(char *buf, char *end, const void 
*ptr,
        if (static_branch_unlikely(&not_filled_random_ptr_key)) {
                spec.field_width = 2 * sizeof(ptr);
                /* string length must be less than default_width */
-               return string_nocheck(buf, end, str, spec);
+               return error_string(buf, end, str, spec);
        }
 
 #ifdef CONFIG_64BIT
@@ -777,7 +792,7 @@ char *restricted_pointer(char *buf, char *end, const void 
*ptr,
                if (in_irq() || in_serving_softirq() || in_nmi()) {
                        if (spec.field_width == -1)
                                spec.field_width = 2 * sizeof(ptr);
-                       return string_nocheck(buf, end, "pK-error", spec);
+                       return error_string(buf, end, "pK-error", spec);
                }
 
                /*
@@ -1511,12 +1526,12 @@ char *ip_addr_string(char *buf, char *end, const void 
*ptr,
                case AF_INET6:
                        return ip6_addr_string_sa(buf, end, &sa->v6, spec, fmt);
                default:
-                       return string_nocheck(buf, end, "(einval)", spec);
+                       return error_string(buf, end, "(einval)", spec);
                }}
        }
 
        err_fmt_msg = fmt[0] == 'i' ? "(%pi?)" : "(%pI?)";
-       return string_nocheck(buf, end, err_fmt_msg, spec);
+       return error_string(buf, end, err_fmt_msg, spec);
 }
 
 static noinline_for_stack
@@ -1653,7 +1668,7 @@ char *netdev_bits(char *buf, char *end, const void *addr,
                size = sizeof(netdev_features_t);
                break;
        default:
-               return string_nocheck(buf, end, "(%pN?)", spec);
+               return error_string(buf, end, "(%pN?)", spec);
        }
 
        return special_hex_number(buf, end, num, size);
@@ -1765,7 +1780,7 @@ char *time_and_date(char *buf, char *end, void *ptr, 
struct printf_spec spec,
        case 'R':
                return rtc_str(buf, end, (const struct rtc_time *)ptr, spec, 
fmt);
        default:
-               return string_nocheck(buf, end, "(%ptR?)", spec);
+               return error_string(buf, end, "(%ptR?)", spec);
        }
 }
 
@@ -1774,7 +1789,7 @@ char *clock(char *buf, char *end, struct clk *clk, struct 
printf_spec spec,
            const char *fmt)
 {
        if (!IS_ENABLED(CONFIG_HAVE_CLK))
-               return string_nocheck(buf, end, "(%pC?)", spec);
+               return error_string(buf, end, "(%pC?)", spec);
 
        if (check_pointer(&buf, end, clk, spec))
                return buf;
@@ -1785,7 +1800,7 @@ char *clock(char *buf, char *end, struct clk *clk, struct 
printf_spec spec,
 #ifdef CONFIG_COMMON_CLK
                return string(buf, end, __clk_get_name(clk), spec);
 #else
-               return string_nocheck(buf, end, "(%pC?)", spec);
+               return error_string(buf, end, "(%pC?)", spec);
 #endif
        }
 }
@@ -1843,7 +1858,7 @@ char *flags_string(char *buf, char *end, void *flags_ptr,
                names = gfpflag_names;
                break;
        default:
-               return string_nocheck(buf, end, "(%pG?)", spec);
+               return error_string(buf, end, "(%pG?)", spec);
        }
 
        return format_flags(buf, end, flags, names);
@@ -1899,7 +1914,7 @@ char *device_node_string(char *buf, char *end, struct 
device_node *dn,
        str_spec.field_width = -1;
 
        if (!IS_ENABLED(CONFIG_OF))
-               return string_nocheck(buf, end, "(%pOF?)", spec);
+               return error_string(buf, end, "(%pOF?)", spec);
 
        if (check_pointer(&buf, end, dn, spec))
                return buf;
@@ -1978,7 +1993,7 @@ static char *kobject_string(char *buf, char *end, void 
*ptr,
                return device_node_string(buf, end, ptr, spec, fmt + 1);
        }
 
-       return string_nocheck(buf, end, "(%pO?)", spec);
+       return error_string(buf, end, "(%pO?)", spec);
 }
 
 /*
-- 
2.16.4