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Message-Id: <20251013-jag-sysctl_conv-v1-6-4dc35ceae733@kernel.org>
Date: Mon, 13 Oct 2025 15:24:56 +0200
From: Joel Granados <joel.granados@...nel.org>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
Kees Cook <kees@...nel.org>
Cc: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
Joel Granados <joel.granados@...nel.org>
Subject: [PATCH 6/8] sysctl: Create converter functions with two new macros
Eight converter functions are created using two new macros
(SYSCTL_USER_TO_KERN_INT_CONV & SYSCTL_KERN_TO_USER_INT_CONV); they are
called from four pre-existing converter functions: do_proc_dointvec_conv
and do_proc_dointvec{,_userhz,_ms}_jiffies_conv. The function names
generated by the macros are differentiated by a string suffix passed as
the first macro argument.
The SYSCTL_USER_TO_KERN_INT_CONV macro first executes the u_ptr_op
operation, then checks for overflow, assigns sign (-, +) and finally
writes to the kernel var with WRITE_ONCE; it always returns an -EINVAL
when an overflow is detected. The SYSCTL_KERN_TO_USER_INT_CONV uses
READ_ONCE, casts to unsigned long, then executes the k_ptr_op before
assigning the value to the user space buffer.
The overflow check is always done against MAX_INT after applying
{k,u}_ptr_op. This approach avoids rounding or precision errors that
might occur when using the inverse operations.
Signed-off-by: Joel Granados <joel.granados@...nel.org>
---
kernel/sysctl.c | 131 ++++++++++++++++++++++++++------------------------------
1 file changed, 61 insertions(+), 70 deletions(-)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 2091d2396c83ac68d621b3d158ce1c490c392c4b..f47bb8af33fb1d2d1a2a7c13d7ca093af82c6400 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -368,31 +368,65 @@ static void proc_put_char(void **buf, size_t *size, char c)
}
}
+#define SYSCTL_USER_TO_KERN_INT_CONV(name, u_ptr_op) \
+int sysctl_user_to_kern_int_conv##name(const bool *negp, \
+ const unsigned long *u_ptr,\
+ int *k_ptr) \
+{ \
+ unsigned long u = u_ptr_op(*u_ptr); \
+ if (*negp) { \
+ if (u > (unsigned long) INT_MAX + 1) \
+ return -EINVAL; \
+ WRITE_ONCE(*k_ptr, -u); \
+ } else { \
+ if (u > (unsigned long) INT_MAX) \
+ return -EINVAL; \
+ WRITE_ONCE(*k_ptr, u); \
+ } \
+ return 0; \
+}
+
+#define SYSCTL_KERN_TO_USER_INT_CONV(name, k_ptr_op) \
+int sysctl_kern_to_user_int_conv##name(bool *negp, \
+ unsigned long *u_ptr, \
+ const int *k_ptr) \
+{ \
+ int val = READ_ONCE(*k_ptr); \
+ if (val < 0) { \
+ *negp = true; \
+ *u_ptr = -k_ptr_op((unsigned long)val); \
+ } else { \
+ *negp = false; \
+ *u_ptr = k_ptr_op((unsigned long)val); \
+ } \
+ return 0; \
+}
+
+#define SYSCTL_CONV_IDENTITY(val) val
+#define SYSCTL_CONV_MULT_HZ(val) ((val) * HZ)
+#define SYSCTL_CONV_DIV_HZ(val) ((val) / HZ)
+
+static SYSCTL_USER_TO_KERN_INT_CONV(, SYSCTL_CONV_IDENTITY)
+static SYSCTL_KERN_TO_USER_INT_CONV(, SYSCTL_CONV_IDENTITY)
+
+static SYSCTL_USER_TO_KERN_INT_CONV(_hz, SYSCTL_CONV_MULT_HZ)
+static SYSCTL_KERN_TO_USER_INT_CONV(_hz, SYSCTL_CONV_DIV_HZ)
+
+static SYSCTL_USER_TO_KERN_INT_CONV(_userhz, clock_t_to_jiffies)
+static SYSCTL_KERN_TO_USER_INT_CONV(_userhz, jiffies_to_clock_t)
+
+static SYSCTL_USER_TO_KERN_INT_CONV(_ms, msecs_to_jiffies)
+static SYSCTL_KERN_TO_USER_INT_CONV(_ms, jiffies_to_msecs)
+
static int do_proc_dointvec_conv(bool *negp, unsigned long *u_ptr,
int *k_ptr, int dir,
const struct ctl_table *table)
{
if (SYSCTL_USER_TO_KERN(dir)) {
- if (*negp) {
- if (*u_ptr > (unsigned long) INT_MAX + 1)
- return -EINVAL;
- WRITE_ONCE(*k_ptr, -*u_ptr);
- } else {
- if (*u_ptr > (unsigned long) INT_MAX)
- return -EINVAL;
- WRITE_ONCE(*k_ptr, *u_ptr);
- }
- } else {
- int val = READ_ONCE(*k_ptr);
- if (val < 0) {
- *negp = true;
- *u_ptr = -(unsigned long)val;
- } else {
- *negp = false;
- *u_ptr = (unsigned long)val;
- }
+ return sysctl_user_to_kern_int_conv(negp, u_ptr, k_ptr);
}
- return 0;
+
+ return sysctl_kern_to_user_int_conv(negp, u_ptr, k_ptr);
}
static int do_proc_douintvec_conv(unsigned long *u_ptr,
@@ -952,31 +986,14 @@ int proc_doulongvec_ms_jiffies_minmax(const struct ctl_table *table, int dir,
lenp, ppos, HZ, 1000l);
}
-
static int do_proc_dointvec_jiffies_conv(bool *negp, unsigned long *u_ptr,
int *k_ptr, int dir,
const struct ctl_table *table)
{
if (SYSCTL_USER_TO_KERN(dir)) {
- if (*u_ptr > INT_MAX / HZ)
- return 1;
- if (*negp)
- WRITE_ONCE(*k_ptr, -*u_ptr * HZ);
- else
- WRITE_ONCE(*k_ptr, *u_ptr * HZ);
- } else {
- int val = READ_ONCE(*k_ptr);
- unsigned long lval;
- if (val < 0) {
- *negp = true;
- lval = -(unsigned long)val;
- } else {
- *negp = false;
- lval = (unsigned long)val;
- }
- *u_ptr = lval / HZ;
+ return sysctl_user_to_kern_int_conv_hz(negp, u_ptr, k_ptr);
}
- return 0;
+ return sysctl_kern_to_user_int_conv_hz(negp, u_ptr, k_ptr);
}
static int do_proc_dointvec_userhz_jiffies_conv(bool *negp, unsigned long *u_ptr,
@@ -984,22 +1001,11 @@ static int do_proc_dointvec_userhz_jiffies_conv(bool *negp, unsigned long *u_ptr
const struct ctl_table *table)
{
if (SYSCTL_USER_TO_KERN(dir)) {
- if (USER_HZ < HZ && (LONG_MAX / HZ) * USER_HZ < *u_ptr)
- return 1;
- *k_ptr = clock_t_to_jiffies(*negp ? -*u_ptr : *u_ptr);
- } else {
- int val = *k_ptr;
- unsigned long lval;
- if (val < 0) {
- *negp = true;
- lval = -(unsigned long)val;
- } else {
- *negp = false;
- lval = (unsigned long)val;
- }
- *u_ptr = jiffies_to_clock_t(lval);
+ if (USER_HZ < HZ)
+ return -EINVAL;
+ return sysctl_user_to_kern_int_conv_userhz(negp, u_ptr, k_ptr);
}
- return 0;
+ return sysctl_kern_to_user_int_conv_userhz(negp, u_ptr, k_ptr);
}
static int do_proc_dointvec_ms_jiffies_conv(bool *negp, unsigned long *u_ptr,
@@ -1007,24 +1013,9 @@ static int do_proc_dointvec_ms_jiffies_conv(bool *negp, unsigned long *u_ptr,
const struct ctl_table *table)
{
if (SYSCTL_USER_TO_KERN(dir)) {
- unsigned long jif = msecs_to_jiffies(*negp ? -*u_ptr : *u_ptr);
-
- if (jif > INT_MAX)
- return 1;
- WRITE_ONCE(*k_ptr, (int)jif);
- } else {
- int val = READ_ONCE(*k_ptr);
- unsigned long lval;
- if (val < 0) {
- *negp = true;
- lval = -(unsigned long)val;
- } else {
- *negp = false;
- lval = (unsigned long)val;
- }
- *u_ptr = jiffies_to_msecs(lval);
+ return sysctl_user_to_kern_int_conv_ms(negp, u_ptr, k_ptr);
}
- return 0;
+ return sysctl_kern_to_user_int_conv_ms(negp, u_ptr, k_ptr);
}
static int do_proc_dointvec_ms_jiffies_minmax_conv(bool *negp, unsigned long *u_ptr,
--
2.50.1
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