[PATCH V11 2/5] vsprintf: refactor %pK code out of pointer()

Tobin C. Harding
2017-11-29T02:06:44Z

Currently code to handle %pK is all within the switch statement in
pointer(). This is the wrong level of abstraction. Each of the other switch
clauses call a helper function, pK should do the same.

Refactor code out of pointer() to new function restricted_pointer().

Signed-off-by: Tobin C. Harding <me@tobin.cc>
---
lib/vsprintf.c | 97 ++++++++++++++++++++++++++++++++--------------------------
1 file changed, 54 insertions(+), 43 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 1746bae94d41..8dc5cf85cef4 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1343,6 +1343,59 @@ char *uuid_string(char *buf, char *end, const u8 *addr,
return string(buf, end, uuid, spec);
}

+int kptr_restrict __read_mostly;
+
+static noinline_for_stack
+char *restricted_pointer(char *buf, char *end, const void *ptr,
+ struct printf_spec spec)
+{
+ spec.base = 16;
+ spec.flags |= SMALL;
+ if (spec.field_width == -1) {
+ spec.field_width = 2 * sizeof(ptr);
+ spec.flags |= ZEROPAD;
+ }
+
+ switch (kptr_restrict) {
+ case 0:
+ /* Always print %pK values */
+ break;
+ case 1: {
+ const struct cred *cred;
+
+ /*
+ * kptr_restrict==1 cannot be used in IRQ context
+ * because its test for CAP_SYSLOG would be meaningless.
+ */
+ if (in_irq() || in_serving_softirq() || in_nmi())
+ return string(buf, end, "pK-error", spec);
+
+ /*
+ * Only print the real pointer value if the current
+ * process has CAP_SYSLOG and is running with the
+ * same credentials it started with. This is because
+ * access to files is checked at open() time, but %pK
+ * checks permission at read() time. We don't want to
+ * leak pointer values if a binary opens a file using
+ * %pK and then elevates privileges before reading it.
+ */
+ cred = current_cred();
+ if (!has_capability_noaudit(current, CAP_SYSLOG) ||
+ !uid_eq(cred->euid, cred->uid) ||
+ !gid_eq(cred->egid, cred->gid))
+ ptr = NULL;
+ break;
+ }
+ case 2:
+ default:
+ /* Always print 0's for %pK */
+ ptr = NULL;
+ break;
+ }
+
+ return number(buf, end, (unsigned long)ptr, spec);
+}
+
static noinline_for_stack
char *netdev_bits(char *buf, char *end, const void *addr, const char *fmt)
{
@@ -1591,8 +1644,6 @@ char *device_node_string(char *buf, char *end, struct device_node *dn,
return widen_string(buf, buf - buf_start, end, spec);
}

-int kptr_restrict __read_mostly;
-
/*
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
@@ -1792,47 +1843,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
return buf;
}
case 'K':
- switch (kptr_restrict) {
- case 0:
- /* Always print %pK values */
- break;
- case 1: {
- const struct cred *cred;
-
- /*
- * kptr_restrict==1 cannot be used in IRQ context
- * because its test for CAP_SYSLOG would be meaningless.
- */
- if (in_irq() || in_serving_softirq() || in_nmi()) {
- if (spec.field_width == -1)
- spec.field_width = default_width;
- return string(buf, end, "pK-error", spec);
- }
-
- /*
- * Only print the real pointer value if the current
- * process has CAP_SYSLOG and is running with the
- * same credentials it started with. This is because
- * access to files is checked at open() time, but %pK
- * checks permission at read() time. We don't want to
- * leak pointer values if a binary opens a file using
- * %pK and then elevates privileges before reading it.
- */
- cred = current_cred();
- if (!has_capability_noaudit(current, CAP_SYSLOG) ||
- !uid_eq(cred->euid, cred->uid) ||
- !gid_eq(cred->egid, cred->gid))
- ptr = NULL;
- break;
- }
- case 2:
- default:
- /* Always print 0's for %pK */
- ptr = NULL;
- break;
- }
- break;
-
+ return restricted_pointer(buf, end, ptr, spec);
case 'N':
return netdev_bits(buf, end, ptr, fmt);
case 'a':
--
2.7.4