Re: [PATCH v5] sysctl: simplify the min/max boundary check
From: Wen Yang
Date: Sun Jan 19 2025 - 10:00:29 EST
On 2025/1/16 17:37, Joel Granados wrote:
On Sun, Jan 05, 2025 at 11:28:53PM +0800, Wen Yang wrote:
do_proc_dointvec_conv() used the default range of int type, while
do_proc_dointvec_minmax_conv() additionally used "int * {min, max}" of
struct do_proc_dointvec_minmax_conv_param, which are actually passed
in table->extra{1,2} pointers.
By changing the struct do_proc_dointvec_minmax_conv_param's
"int * {min, max}" to "int {min, max}" and setting the min/max value
via dereference the table->extra{1, 2}, those do_proc_dointvec_conv() and
do_proc_dointvec_minmax_conv() functions can be merged into one and reduce
code by one-third.
Similar changes were also made for do_proc_douintvec_minmax_conv_param,
do_proc_douintvec_conv() and do_proc_douintvec_minmax_conv().
Before moving forward, I need the motivation.
Please answer this:
*Why* are you pushing these two [1], [2] series?
Best
[1]
* https://lore.kernel.org/tencent_A7FD9E9E75AA74A87583A427F5D20F988B09@xxxxxx
* https://lore.kernel.org/tencent_C5E6023F97E7CC2A046AAEA09BC9ACF43907@xxxxxx
* https://lore.kernel.org/cover.1726365007.git.wen.yang@xxxxxxxxx
* https://lore.kernel.org/cover.1726910671.git.wen.yang@xxxxxxxxx
[2]
* https://lore.kernel.org/20240714173858.52163-1-wen.yang@xxxxxxxxx
* https://lore.kernel.org/20240715150223.54707-1-wen.yang@xxxxxxxxx
* https://lore.kernel.org/20240905134818.4104-1-wen.yang@xxxxxxxxx
* https://lore.kernel.org/20241201140058.5653-1-wen.yang@xxxxxxxxx
Thank you for your comments.
Here is a brief report about it.
The boundary check of sysctl uses .extra{1, 2} pointers, which need to
point to constant variables (such as two_five_five, n_65535, ue_int_max,
etc. that appear in multiple modules).
We first try to stuff these variables into the shared const arrays (
(sysctl_vals, sysctl_long_vals) to save memory, as shown in series 1.
Thank Eric for pointing out:
- You can still save a lot more by turning .extra1 and .extra2
- into longs instead of keeping them as pointers and needing
- constants to be pointed at somewhere.
We have further found more detailed information about "kill the shared
const array":
https://lkml.kernel.org/87zgpte9o4.fsf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
67ff32289 ("proc_sysctl: update docs for __register_sysctl_table()")
So we tried some ways to achieve it, as shown in series 2.
Step 1: The extra{1,2} pointer is used as {min, max} pointers in the
do_proc_do{int, uint}vec_minmax_conv_param structures. By changing the
{min, max} pointers to numeric values, the code is simplified and
preparations are made for the second step.
Step 2: Add some sysctl helper functions to avoid direct access to
table->extra1/extra2, and also support encoding values directly in the
table entry.
https://lore.kernel.org/all/0f4a5233b75e6484a6236d85d2b506c96ea41ef1.1726910671.git.wen.yang@xxxxxxxxx/
https://lore.kernel.org/all/a086609632328c2feee69b10067e43115885b2ae.1726910671.git.wen.yang@xxxxxxxxx/
Step 3: gradually remove the extra constant variables in multiple modules.
https://lore.kernel.org/all/5f753895a5f31cac65ddeb56b58fc17553785163.1726910671.git.wen.yang@xxxxxxxxx/
https://lore.kernel.org/all/20d67551ed7fa9c774d2b128ad9bc298a0a55c9d.1726910671.git.wen.yang@xxxxxxxxx/
--
Best wishes,
Wen
Selftest were also made:
[23:16:38] ================ sysctl_test (11 subtests) =================
[23:16:38] [PASSED] sysctl_test_api_dointvec_null_tbl_data
[23:16:38] [PASSED] sysctl_test_api_dointvec_table_maxlen_unset
[23:16:38] [PASSED] sysctl_test_api_dointvec_table_len_is_zero
[23:16:38] [PASSED] sysctl_test_api_dointvec_table_read_but_position_set
[23:16:38] [PASSED] sysctl_test_dointvec_read_happy_single_positive
[23:16:38] [PASSED] sysctl_test_dointvec_read_happy_single_negative
[23:16:38] [PASSED] sysctl_test_dointvec_write_happy_single_positive
[23:16:38] [PASSED] sysctl_test_dointvec_write_happy_single_negative
[23:16:38] [PASSED] sysctl_test_api_dointvec_write_single_less_int_min
[23:16:38] [PASSED] sysctl_test_api_dointvec_write_single_greater_int_max
[23:16:38] [PASSED] sysctl_test_register_sysctl_sz_invalid_extra_value
[23:16:38] =================== [PASSED] sysctl_test ===================
[23:16:38] ============================================================
[23:16:38] Testing complete. Ran 11 tests: passed: 11
Signed-off-by: Wen Yang <wen.yang@xxxxxxxxx>
Cc: Joel Granados <joel.granados@xxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
kernel/sysctl.c | 211 ++++++++++++++++++++----------------------------
1 file changed, 86 insertions(+), 125 deletions(-)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 7ae7a4136855..250dc9057259 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -424,22 +424,44 @@ static void proc_put_char(void **buf, size_t *size, char c)
}
}
-static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
- int *valp,
- int write, void *data)
+/**
+ * struct do_proc_dointvec_minmax_conv_param - proc_dointvec_minmax() range checking structure
+ * @min: the minimum allowable value
+ * @max: the maximum allowable value
+ *
+ * The do_proc_dointvec_minmax_conv_param structure provides the
+ * minimum and maximum values for doing range checking for those sysctl
+ * parameters that use the proc_dointvec_minmax(), proc_dou8vec_minmax() and so on.
+ */
+struct do_proc_dointvec_minmax_conv_param {
+ int min;
+ int max;
+};
+
+static inline int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
+ int *valp,
+ int write, void *data)
{
+ struct do_proc_dointvec_minmax_conv_param *param = data;
+ long min, max;
+ long val;
+
if (write) {
if (*negp) {
- if (*lvalp > (unsigned long) INT_MAX + 1)
- return -EINVAL;
- WRITE_ONCE(*valp, -*lvalp);
+ max = param ? param->max : 0;
+ min = param ? param->min : INT_MIN;
+ val = -*lvalp;
} else {
- if (*lvalp > (unsigned long) INT_MAX)
- return -EINVAL;
- WRITE_ONCE(*valp, *lvalp);
+ max = param ? param->max : INT_MAX;
+ min = param ? param->min : 0;
+ val = *lvalp;
}
+
+ if (val > max || val < min)
+ return -EINVAL;
+ WRITE_ONCE(*valp, (int)val);
} else {
- int val = READ_ONCE(*valp);
+ val = (int)READ_ONCE(*valp);
if (val < 0) {
*negp = true;
*lvalp = -(unsigned long)val;
@@ -448,21 +470,44 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
*lvalp = (unsigned long)val;
}
}
+
return 0;
}
-static int do_proc_douintvec_conv(unsigned long *lvalp,
- unsigned int *valp,
- int write, void *data)
+/**
+ * struct do_proc_douintvec_minmax_conv_param - proc_douintvec_minmax() range checking structure
+ * @min: minimum allowable value
+ * @max: maximum allowable value
+ *
+ * The do_proc_douintvec_minmax_conv_param structure provides the
+ * minimum and maximum values for doing range checking for those sysctl
+ * parameters that use the proc_douintvec_minmax() handler.
+ */
+struct do_proc_douintvec_minmax_conv_param {
+ unsigned int min;
+ unsigned int max;
+};
+
+static inline int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
+ unsigned int *valp,
+ int write, void *data)
{
+ struct do_proc_douintvec_minmax_conv_param *param = data;
+ unsigned long min, max;
+
if (write) {
- if (*lvalp > UINT_MAX)
+ max = param ? param->max : UINT_MAX;
+ min = param ? param->min : 0;
+
+ if (*lvalp > max || *lvalp < min)
return -EINVAL;
- WRITE_ONCE(*valp, *lvalp);
+
+ WRITE_ONCE(*valp, (unsigned int)*lvalp);
} else {
unsigned int val = READ_ONCE(*valp);
*lvalp = (unsigned long)val;
}
+
return 0;
}
@@ -489,7 +534,7 @@ static int __do_proc_dointvec(void *tbl_data, const struct ctl_table *table,
left = *lenp;
if (!conv)
- conv = do_proc_dointvec_conv;
+ conv = do_proc_dointvec_minmax_conv;
if (write) {
if (proc_first_pos_non_zero_ignore(ppos, table))
@@ -667,7 +712,7 @@ static int __do_proc_douintvec(void *tbl_data, const struct ctl_table *table,
}
if (!conv)
- conv = do_proc_douintvec_conv;
+ conv = do_proc_douintvec_minmax_conv;
if (write)
return do_proc_douintvec_w(i, table, buffer, lenp, ppos,
@@ -762,7 +807,7 @@ int proc_douintvec(const struct ctl_table *table, int write, void *buffer,
size_t *lenp, loff_t *ppos)
{
return do_proc_douintvec(table, write, buffer, lenp, ppos,
- do_proc_douintvec_conv, NULL);
+ do_proc_douintvec_minmax_conv, NULL);
}
/*
@@ -808,46 +853,6 @@ static int proc_taint(const struct ctl_table *table, int write,
return err;
}
-/**
- * struct do_proc_dointvec_minmax_conv_param - proc_dointvec_minmax() range checking structure
- * @min: pointer to minimum allowable value
- * @max: pointer to maximum allowable value
- *
- * The do_proc_dointvec_minmax_conv_param structure provides the
- * minimum and maximum values for doing range checking for those sysctl
- * parameters that use the proc_dointvec_minmax() handler.
- */
-struct do_proc_dointvec_minmax_conv_param {
- int *min;
- int *max;
-};
-
-static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
- int *valp,
- int write, void *data)
-{
- int tmp, ret;
- struct do_proc_dointvec_minmax_conv_param *param = data;
- /*
- * If writing, first do so via a temporary local int so we can
- * bounds-check it before touching *valp.
- */
- int *ip = write ? &tmp : valp;
-
- ret = do_proc_dointvec_conv(negp, lvalp, ip, write, data);
- if (ret)
- return ret;
-
- if (write) {
- if ((param->min && *param->min > tmp) ||
- (param->max && *param->max < tmp))
- return -EINVAL;
- WRITE_ONCE(*valp, tmp);
- }
-
- return 0;
-}
-
/**
* proc_dointvec_minmax - read a vector of integers with min/max values
* @table: the sysctl table
@@ -867,53 +872,14 @@ static int do_proc_dointvec_minmax_conv(bool *negp, unsigned long *lvalp,
int proc_dointvec_minmax(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
- struct do_proc_dointvec_minmax_conv_param param = {
- .min = (int *) table->extra1,
- .max = (int *) table->extra2,
- };
+ struct do_proc_dointvec_minmax_conv_param param;
+
+ param.min = (table->extra1) ? *(int *) table->extra1 : INT_MIN;
+ param.max = (table->extra2) ? *(int *) table->extra2 : INT_MAX;
return do_proc_dointvec(table, write, buffer, lenp, ppos,
do_proc_dointvec_minmax_conv, ¶m);
}
-/**
- * struct do_proc_douintvec_minmax_conv_param - proc_douintvec_minmax() range checking structure
- * @min: pointer to minimum allowable value
- * @max: pointer to maximum allowable value
- *
- * The do_proc_douintvec_minmax_conv_param structure provides the
- * minimum and maximum values for doing range checking for those sysctl
- * parameters that use the proc_douintvec_minmax() handler.
- */
-struct do_proc_douintvec_minmax_conv_param {
- unsigned int *min;
- unsigned int *max;
-};
-
-static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
- unsigned int *valp,
- int write, void *data)
-{
- int ret;
- unsigned int tmp;
- struct do_proc_douintvec_minmax_conv_param *param = data;
- /* write via temporary local uint for bounds-checking */
- unsigned int *up = write ? &tmp : valp;
-
- ret = do_proc_douintvec_conv(lvalp, up, write, data);
- if (ret)
- return ret;
-
- if (write) {
- if ((param->min && *param->min > tmp) ||
- (param->max && *param->max < tmp))
- return -ERANGE;
-
- WRITE_ONCE(*valp, tmp);
- }
-
- return 0;
-}
-
/**
* proc_douintvec_minmax - read a vector of unsigned ints with min/max values
* @table: the sysctl table
@@ -936,10 +902,11 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
int proc_douintvec_minmax(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
- struct do_proc_douintvec_minmax_conv_param param = {
- .min = (unsigned int *) table->extra1,
- .max = (unsigned int *) table->extra2,
- };
+ struct do_proc_douintvec_minmax_conv_param param;
+
+ param.min = (table->extra1) ? *(unsigned int *) table->extra1 : 0;
+ param.max = (table->extra2) ? *(unsigned int *) table->extra2 : UINT_MAX;
+
return do_proc_douintvec(table, write, buffer, lenp, ppos,
do_proc_douintvec_minmax_conv, ¶m);
}
@@ -965,23 +932,17 @@ int proc_dou8vec_minmax(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
struct ctl_table tmp;
- unsigned int min = 0, max = 255U, val;
+ unsigned int val;
u8 *data = table->data;
- struct param = {
- .min = &min,
- .max = &max,
- };
+ struct do_proc_douintvec_minmax_conv_param param;
int res;
/* Do not support arrays yet. */
if (table->maxlen != sizeof(u8))
return -EINVAL;
- if (table->extra1)
- min = *(unsigned int *) table->extra1;
- if (table->extra2)
- max = *(unsigned int *) table->extra2;
-
+ param.min = (table->extra1) ? *(unsigned int *) table->extra1 : 0;
+ param.max = (table->extra2) ? *(unsigned int *) table->extra2 : 255U;
tmp = *table;
tmp.maxlen = sizeof(val);
@@ -1022,7 +983,7 @@ static int __do_proc_doulongvec_minmax(void *data,
void *buffer, size_t *lenp, loff_t *ppos,
unsigned long convmul, unsigned long convdiv)
{
- unsigned long *i, *min, *max;
+ unsigned long *i, min, max;
int vleft, first = 1, err = 0;
size_t left;
char *p;
@@ -1033,8 +994,9 @@ static int __do_proc_doulongvec_minmax(void *data,
}
i = data;
- min = table->extra1;
- max = table->extra2;
+ min = (table->extra1) ? *(unsigned long *) table->extra1 : 0;
+ max = (table->extra2) ? *(unsigned long *) table->extra2 : ULONG_MAX;
+
vleft = table->maxlen / sizeof(unsigned long);
left = *lenp;
@@ -1066,7 +1028,7 @@ static int __do_proc_doulongvec_minmax(void *data,
}
val = convmul * val / convdiv;
- if ((min && val < *min) || (max && val > *max)) {
+ if ((val < min) || (val > max)) {
err = -EINVAL;
break;
}
@@ -1236,8 +1198,7 @@ static int do_proc_dointvec_ms_jiffies_minmax_conv(bool *negp, unsigned long *lv
return ret;
if (write) {
- if ((param->min && *param->min > tmp) ||
- (param->max && *param->max < tmp))
+ if ((param->min > tmp) || (param->max < tmp))
return -EINVAL;
*valp = tmp;
}
@@ -1269,10 +1230,10 @@ int proc_dointvec_jiffies(const struct ctl_table *table, int write,
int proc_dointvec_ms_jiffies_minmax(const struct ctl_table *table, int write,
void *buffer, size_t *lenp, loff_t *ppos)
{
- struct do_proc_dointvec_minmax_conv_param param = {
- .min = (int *) table->extra1,
- .max = (int *) table->extra2,
- };
+ struct do_proc_dointvec_minmax_conv_param param;
+
+ param.min = (table->extra1) ? *(int *) table->extra1 : INT_MIN;
+ param.max = (table->extra2) ? *(int *) table->extra2 : INT_MAX;
return do_proc_dointvec(table, write, buffer, lenp, ppos,
do_proc_dointvec_ms_jiffies_minmax_conv, ¶m);
}
--
2.25.1