[PATCH v3 4/4] sysctl: check for UINT_MAX before unsigned int min/max

[Joe Lawrence]

Mikulas noticed in the existing do_proc_douintvec_minmax_conv() and
do_proc_dopipe_max_size_conv() introduced in this patchset, that they
inconsistently handle overflow and min/max range inputs:

For example:

  0 ... param->min - 1 ---> ERANGE
  param->min ... param->max ---> the value is accepted
  param->max + 1 ... 0x100000000L + param->min - 1 ---> ERANGE
  0x100000000L + param->min ... 0x100000000L + param->max ---> EINVAL
  0x100000000L + param->max + 1, 0x200000000L + param->min - 1 ---> ERANGE
  0x200000000L + param->min ... 0x200000000L + param->max ---> EINVAL
  0x200000000L + param->max + 1, 0x300000000L + param->min - 1 ---> ERANGE

In do_proc_do*() routines which store values into unsigned int variables
(4 bytes wide for 64-bit builds), first validate that the input unsigned
long value (8 bytes wide for 64-bit builds) will fit inside the smaller
unsigned int variable.  Then check that the unsigned int value falls
inside the specified parameter min, max range.  Otherwise the unsigned
long -> unsigned int conversion drops leading bits from the input value,
leading to the inconsistent pattern Mikulas documented above.

Reported-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
Signed-off-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
---
 kernel/sysctl.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 30b01b22014d..a04907158c90 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2587,12 +2587,13 @@ static int do_proc_douintvec_minmax_conv(unsigned long *lvalp,
 	if (write) {
 		unsigned int val = *lvalp;
 
+		if (*lvalp > UINT_MAX)
+			return -EINVAL;
+
 		if ((param->min && *param->min > val) ||
 		    (param->max && *param->max < val))
 			return -ERANGE;
 
-		if (*lvalp > UINT_MAX)
-			return -EINVAL;
 		*valp = val;
 	} else {
 		unsigned int val = *valp;
@@ -2643,17 +2644,18 @@ static int do_proc_dopipe_max_size_conv(unsigned long *lvalp,
 	struct do_proc_dopipe_max_size_conv_param *param = data;
 
 	if (write) {
-		unsigned int val = round_pipe_size(*lvalp);
+		unsigned int val;
 
+		if (*lvalp > UINT_MAX)
+			return -EINVAL;
+
+		val = round_pipe_size(*lvalp);
 		if (val == 0)
 			return -EINVAL;
 
 		if (param->min && *param->min > val)
 			return -ERANGE;
 
-		if (*lvalp > UINT_MAX)
-			return -EINVAL;
-
 		*valp = val;
 	} else {
 		unsigned int val = *valp;
-- 
1.8.3.1