[PATCH] sysctl: Handle error writing UINT_MAX to u32 fields

[Subash Abhinov Kasiviswanathan]

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.

Fixes: 230633d109e3 ("kernel/sysctl.c:detect overflows when converting to int")
Cc: Heinrich Schuchardt <xypron.glpk@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Signed-off-by: Subash Abhinov Kasiviswanathan <subashab@xxxxxxxxxxxxxx>
---
 include/linux/sysctl.h |  2 ++
 kernel/sysctl.c        | 42 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 697e160..a4f7203 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -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,
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index b43d0b2..96437af 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -2140,6 +2140,21 @@ static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
 	return 0;
 }
 
+static int do_proc_douintvec_conv(bool *negp, unsigned long *lvalp,
+				 int *valp,
+				 int write, void *data)
+{
+	if (write) {
+		if (*negp)
+			return -EINVAL;
+		*valp = *lvalp;
+	} else {
+		unsigned int val = *valp;
+		*lvalp = (unsigned long)val;
+	}
+	return 0;
+}
+
 static const char proc_wspace_sep[] = { ' ', '\t', '\n' };
 
 static int __do_proc_dointvec(void *tbl_data, struct ctl_table *table,
@@ -2263,6 +2278,26 @@ int proc_dointvec(struct ctl_table *table, int write,
 		    	    NULL,NULL);
 }
 
+/**
+ * proc_douintvec - read a vector of unsigned integers
+ * @table: the sysctl table
+ * @write: %TRUE if this is a write to the sysctl file
+ * @buffer: the user buffer
+ * @lenp: the size of the user buffer
+ * @ppos: file position
+ *
+ * Reads/writes up to table->maxlen/sizeof(unsigned int) unsigned integer
+ * values from/to the user buffer, treated as an ASCII string.
+ *
+ * Returns 0 on success.
+ */
+int proc_douintvec(struct ctl_table *table, int write,
+		     void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+    return do_proc_dointvec(table,write,buffer,lenp,ppos,
+			    do_proc_douintvec_conv, NULL);
+}
+
 /*
  * Taint values can only be increased
  * This means we can safely use a temporary.
@@ -2858,6 +2893,12 @@ int proc_dointvec(struct ctl_table *table, int write,
 	return -ENOSYS;
 }
 
+int proc_douintvec(struct ctl_table *table, int write,
+		  void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+	return -ENOSYS;
+}
+
 int proc_dointvec_minmax(struct ctl_table *table, int write,
 		    void __user *buffer, size_t *lenp, loff_t *ppos)
 {
@@ -2903,6 +2944,7 @@ int proc_doulongvec_ms_jiffies_minmax(struct ctl_table *table, int write,
  * exception granted :-)
  */
 EXPORT_SYMBOL(proc_dointvec);
+EXPORT_SYMBOL(proc_douintvec);
 EXPORT_SYMBOL(proc_dointvec_jiffies);
 EXPORT_SYMBOL(proc_dointvec_minmax);
 EXPORT_SYMBOL(proc_dointvec_userhz_jiffies);
-- 
1.9.1