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Date: Fri, 5 May 2017 21:06:56 -0700
From: Greg KH <gregkh@...uxfoundation.org>
To: kernel-hardening@...ts.openwall.com, Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc: linux-kernel@...r.kernel.org, Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will.deacon@....com>,
Steven Rostedt <rostedt@...dmis.org>,
William Roberts <william.c.roberts@...el.com>,
Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>
Subject: [RFC 1/6] lib: vsprintf: additional kernel pointer filtering options
From: Dave Weinstein <olorin@...gle.com>
Add the kptr_restrict setting of 3 which results in both
%p and %pK values being replaced by zeros.
Add an additional %pP value inspired by the Grsecurity
option which explicitly whitelists pointers for output.
This patch is based on work by William Roberts
<william.c.roberts@...el.com>
Cc: William Roberts <william.c.roberts@...el.com>
Cc: Chris Fries <cfries@...gle.com>
Signed-off-by: Dave Weinstein <olorin@...gle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
Documentation/printk-formats.txt | 5 +++
Documentation/sysctl/kernel.txt | 3 ++
kernel/sysctl.c | 3 +-
lib/vsprintf.c | 81 ++++++++++++++++++++++++++--------------
4 files changed, 63 insertions(+), 29 deletions(-)
diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 5962949944fd..8994c65aa3b0 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -64,6 +64,11 @@ Kernel Pointers:
users. The behaviour of %pK depends on the kptr_restrict sysctl - see
Documentation/sysctl/kernel.txt for more details.
+ %pP 0x01234567 or 0x0123456789abcdef
+
+ For printing kernel pointers which should always be shown, even to
+ unprivileged users.
+
Struct Resources:
%pr [mem 0x60000000-0x6fffffff flags 0x2200] or
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index bac23c198360..c9f5da409868 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -392,6 +392,9 @@ values to unprivileged users is a concern.
When kptr_restrict is set to (2), kernel pointers printed using
%pK will be replaced with 0's regardless of privileges.
+When kptr_restrict is set to (3), kernel pointers printed using
+%p and %pK will be replaced with 0's regardless of privileges.
+
==============================================================
l2cr: (PPC only)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8c8714fcb53c..1bfdd262c66a 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -129,6 +129,7 @@ static unsigned long one_ul = 1;
static int one_hundred = 100;
static int one_thousand = 1000;
#ifdef CONFIG_PRINTK
+static int three = 3;
static int ten_thousand = 10000;
#endif
#ifdef CONFIG_PERF_EVENTS
@@ -830,7 +831,7 @@ static struct ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = proc_dointvec_minmax_sysadmin,
.extra1 = &zero,
- .extra2 = &two,
+ .extra2 = &three,
},
#endif
{
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index e3bf4e0f10b5..f4e11dade1ab 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -395,6 +395,16 @@ struct printf_spec {
#define FIELD_WIDTH_MAX ((1 << 23) - 1)
#define PRECISION_MAX ((1 << 15) - 1)
+int kptr_restrict __read_mostly;
+
+/*
+ * Always cleanse %p and %pK specifiers
+ */
+static inline int kptr_restrict_always_cleanse_pointers(void)
+{
+ return kptr_restrict >= 3;
+}
+
static noinline_for_stack
char *number(char *buf, char *end, unsigned long long num,
struct printf_spec spec)
@@ -1470,8 +1480,6 @@ char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt)
return format_flags(buf, end, flags, names);
}
-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
@@ -1540,6 +1548,7 @@ int kptr_restrict __read_mostly;
* Do not use this feature without some mechanism to verify the
* correctness of the format string and va_list arguments.
* - 'K' For a kernel pointer that should be hidden from unprivileged users
+ * - 'P' For a kernel pointer that should be shown to all users
* - 'NF' For a netdev_features_t
* - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
* a certain separator (' ' by default):
@@ -1569,6 +1578,9 @@ int kptr_restrict __read_mostly;
* Note: The difference between 'S' and 'F' is that on ia64 and ppc64
* function pointers are really function descriptors, which contain a
* pointer to the real address.
+ *
+ * Note: That for kptr_restrict set to 3, %p and %pK have the same
+ * meaning.
*/
static noinline_for_stack
char *pointer(const char *fmt, char *buf, char *end, void *ptr,
@@ -1576,7 +1588,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
{
const int default_width = 2 * sizeof(void *);
- if (!ptr && *fmt != 'K') {
+ if (!ptr && *fmt != 'K' && !kptr_restrict_always_cleanse_pointers()) {
/*
* Print (null) with the same width as a pointer so it makes
* tabular output look nice.
@@ -1657,10 +1669,43 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
va_end(va);
return buf;
}
+ case 'N':
+ return netdev_bits(buf, end, ptr, fmt);
+ case 'a':
+ return address_val(buf, end, ptr, fmt);
+ case 'd':
+ return dentry_name(buf, end, ptr, spec, fmt);
+ case 'C':
+ return clock(buf, end, ptr, spec, fmt);
+ case 'D':
+ return dentry_name(buf, end,
+ ((const struct file *)ptr)->f_path.dentry,
+ spec, fmt);
+#ifdef CONFIG_BLOCK
+ case 'g':
+ return bdev_name(buf, end, ptr, spec, fmt);
+#endif
+
+ case 'G':
+ return flags_string(buf, end, ptr, fmt);
+ case 'P':
+ /*
+ * an explicitly whitelisted kernel pointer should never be
+ * cleansed
+ */
+ break;
+ default:
+ /*
+ * plain %p, no extension, check if we should always cleanse and
+ * treat like %pK.
+ */
+ if (!kptr_restrict_always_cleanse_pointers())
+ break;
+ /* fallthrough */
case 'K':
switch (kptr_restrict) {
case 0:
- /* Always print %pK values */
+ /* Always print %p values */
break;
case 1: {
const struct cred *cred;
@@ -1679,7 +1724,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
* 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
+ * access to files is checked at open() time, but %p
* 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.
@@ -1691,33 +1736,13 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
ptr = NULL;
break;
}
- case 2:
+ case 2: /* restrict only %pK */
+ case 3: /* restrict all non-extensioned %p and %pK */
default:
- /* Always print 0's for %pK */
ptr = NULL;
break;
}
break;
-
- case 'N':
- return netdev_bits(buf, end, ptr, fmt);
- case 'a':
- return address_val(buf, end, ptr, fmt);
- case 'd':
- return dentry_name(buf, end, ptr, spec, fmt);
- case 'C':
- return clock(buf, end, ptr, spec, fmt);
- case 'D':
- return dentry_name(buf, end,
- ((const struct file *)ptr)->f_path.dentry,
- spec, fmt);
-#ifdef CONFIG_BLOCK
- case 'g':
- return bdev_name(buf, end, ptr, spec, fmt);
-#endif
-
- case 'G':
- return flags_string(buf, end, ptr, fmt);
}
spec.flags |= SMALL;
if (spec.field_width == -1) {
@@ -1726,7 +1751,7 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
}
spec.base = 16;
- return number(buf, end, (unsigned long) ptr, spec);
+ return number(buf, end, (unsigned long long) ptr, spec);
}
/*
--
2.12.2
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