sysctl: Handle error writing UINT_MAX to u32 fields

We have scripts which write to certain fields on 3.18 kernels but this seems to be failing on 4.4 kernels. An entry which we write to here is xfrm_aevent_rseqth which is u32.

echo 4294967295 > /proc/sys/net/core/xfrm_aevent_rseqth

Commit 230633d109e3 ("kernel/sysctl.c: detect overflows when converting to int") prevented writing to sysctl entries when integer overflow occurs. However, this does not apply to unsigned integers.

Heinrich suggested that we introduce a new option to handle 64 bit limits and set min as 0 and max as UINT_MAX. This might not work as it leads to issues similar to __do_proc_doulongvec_minmax. Alternatively, we would need to change the datatype of the entry to 64 bit.

static int __do_proc_doulongvec_minmax(void *data, struct ctl_table {
i = (unsigned long *) data; //This cast is causing to
read beyond the size of data (u32)

    vleft = table->maxlen / sizeof(unsigned long); //vleft is 0

because maxlen is sizeof(u32) which is lesser than sizeof(unsigned long) on x86_64.

Introduce a new proc handler proc_douintvec. Individual proc entries will need to be updated to use the new handler.

---
 include/linux/sysctl.h |  2 ++
 kernel/sysctl.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

index 697e160..a4f7203 100644
@@ -42,6 +42,8 @@ extern int proc_dostring(struct ctl_table *, int,
 			 void __user *, size_t *, loff_t *);
 extern int proc_dointvec(struct ctl_table *, int,
 			 void __user *, size_t *, loff_t *);
+extern int proc_douintvec(struct ctl_table *, int,
+			 void __user *, size_t *, loff_t *);
 extern int proc_dointvec_minmax(struct ctl_table *, int,
 				void __user *, size_t *, loff_t *);
 extern int proc_dointvec_jiffies(struct ctl_table *, int,

1.9.1