sysctl: fix proc_dobool() usability

Currently proc_dobool expects a (bool *) in table->data, but sizeof(int)
in table->maxsize, because it uses do_proc_dointvec() directly.

This is unsafe for at least two reasons:
1. A sysctl table definition may use { .data = &variable, .maxsize =
   sizeof(variable) }, not realizing that this makes the sysctl unusable
   (see the Fixes: tag) and that they need to use the completely
   counterintuitive sizeof(int) instead.
2. proc_dobool() will currently try to parse an array of values if given
   .maxsize >= 2*sizeof(int), but will try to write values of type bool
   by offsets of sizeof(int), so it will not work correctly with neither
   an (int *) nor a (bool *). There is no .maxsize validation to prevent
   this.

Fix this by:
1. Constraining proc_dobool() to allow only one value and .maxsize ==
   sizeof(bool).
2. Wrapping the original struct ctl_table in a temporary one with .data
   pointing to a local int variable and .maxsize set to sizeof(int) and
   passing this one to proc_dointvec(), converting the value to/from
   bool as needed (using proc_dou8vec_minmax() as an example).
3. Extending sysctl_check_table() to enforce proc_dobool() expectations.
4. Fixing the proc_dobool() docstring (it was just copy-pasted from
   proc_douintvec, apparently...).
5. Converting all existing proc_dobool() users to set .maxsize to
   sizeof(bool) instead of sizeof(int).

Fixes: 83efeeeb3d04 ("tty: Allow TIOCSTI to be disabled")
Fixes: a2071573d634 ("sysctl: introduce new proc handler proc_dobool")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index 59ef8a1..914ea1c 100644 (file)
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -496,7 +496,7 @@ static struct ctl_table nlm_sysctls[] = {
        {
                .procname       = "nsm_use_hostnames",
                .data           = &nsm_use_hostnames,
-               .maxlen         = sizeof(int),
+               .maxlen         = sizeof(bool),
                .mode           = 0644,
                .proc_handler   = proc_dobool,
        },

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index e89bd8f..5851eb5 100644 (file)
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -1124,6 +1124,11 @@ static int sysctl_check_table_array(const char *path, struct ctl_table *table)
                        err |= sysctl_err(path, table, "array not allowed");
        }
 
+       if (table->proc_handler == proc_dobool) {
+               if (table->maxlen != sizeof(bool))
+                       err |= sysctl_err(path, table, "array not allowed");
+       }
+
        return err;
 }
 
@@ -1136,6 +1141,7 @@ static int sysctl_check_table(const char *path, struct ctl_table *table)
                        err |= sysctl_err(path, entry, "Not a file");
 
                if ((entry->proc_handler == proc_dostring) ||
+                   (entry->proc_handler == proc_dobool) ||
                    (entry->proc_handler == proc_dointvec) ||
                    (entry->proc_handler == proc_douintvec) ||
                    (entry->proc_handler == proc_douintvec_minmax) ||

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 137d4ab..1c240d2 100644 (file)
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -425,21 +425,6 @@ static void proc_put_char(void **buf, size_t *size, char c)
        }
 }
 
-static int do_proc_dobool_conv(bool *negp, unsigned long *lvalp,
-                               int *valp,
-                               int write, void *data)
-{
-       if (write) {
-               *(bool *)valp = *lvalp;
-       } else {
-               int val = *(bool *)valp;
-
-               *lvalp = (unsigned long)val;
-               *negp = false;
-       }
-       return 0;
-}
-
 static int do_proc_dointvec_conv(bool *negp, unsigned long *lvalp,
                                 int *valp,
                                 int write, void *data)
@@ -710,16 +695,36 @@ int do_proc_douintvec(struct ctl_table *table, int write,
  * @lenp: the size of the user buffer
  * @ppos: file position
  *
- * Reads/writes up to table->maxlen/sizeof(unsigned int) integer
- * values from/to the user buffer, treated as an ASCII string.
+ * Reads/writes one integer value from/to the user buffer,
+ * treated as an ASCII string.
+ *
+ * table->data must point to a bool variable and table->maxlen must
+ * be sizeof(bool).
  *
  * Returns 0 on success.
  */
 int proc_dobool(struct ctl_table *table, int write, void *buffer,
                size_t *lenp, loff_t *ppos)
 {
-       return do_proc_dointvec(table, write, buffer, lenp, ppos,
-                               do_proc_dobool_conv, NULL);
+       struct ctl_table tmp;
+       bool *data = table->data;
+       int res, val;
+
+       /* Do not support arrays yet. */
+       if (table->maxlen != sizeof(bool))
+               return -EINVAL;
+
+       tmp = *table;
+       tmp.maxlen = sizeof(val);
+       tmp.data = &val;
+
+       val = READ_ONCE(*data);
+       res = proc_dointvec(&tmp, write, buffer, lenp, ppos);
+       if (res)
+               return res;
+       if (write)
+               WRITE_ONCE(*data, val);
+       return 0;
 }
 
 /**

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 45e93a5..a559037 100644 (file)
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -581,7 +581,7 @@ static struct ctl_table hugetlb_vmemmap_sysctls[] = {
        {
                .procname       = "hugetlb_optimize_vmemmap",
                .data           = &vmemmap_optimize_enabled,
-               .maxlen         = sizeof(int),
+               .maxlen         = sizeof(vmemmap_optimize_enabled),
                .mode           = 0644,
                .proc_handler   = proc_dobool,
        },