dm ioctl: optimize functions without variable params

Device-mapper ioctls receive and send data in a buffer supplied
by userspace.  The buffer has two parts.  The first part contains
a 'struct dm_ioctl' and has a fixed size.  The second part depends
on the ioctl and has a variable size.

This patch recognises the specific ioctls that do not use the variable
part of the buffer and skips allocating memory for it.

In particular, when a device is suspended and a resume ioctl is sent,
this now avoid memory allocation completely.

The variable "struct dm_ioctl tmp" is moved from the function
copy_params to its caller ctl_ioctl and renamed to param_kernel.
It is used directly when the ioctl function doesn't need any arguments.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 34 insertions, 18 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 9ae11b2994f8..7eb0682d574f 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1560,7 +1560,8 @@ static int check_version(unsigned int cmd, struct dm_ioctl __user *user)
         return r;
 }
 
-#define DM_PARAMS_VMALLOC       0x0001  /* Params alloced with vmalloc not kmalloc */
+#define DM_PARAMS_KMALLOC       0x0001  /* Params alloced with kmalloc */
+#define DM_PARAMS_VMALLOC       0x0002  /* Params alloced with vmalloc */
 #define DM_WIPE_BUFFER          0x0010  /* Wipe input buffer before returning from ioctl */
 
 static void free_params(struct dm_ioctl *param, size_t param_size, int param_flags)
@@ -1568,66 +1569,80 @@ static void free_params(struct dm_ioctl *param, size_t param_size, int param_fla
         if (param_flags & DM_WIPE_BUFFER)
                 memset(param, 0, param_size);
 
+        if (param_flags & DM_PARAMS_KMALLOC)
+                kfree(param);
         if (param_flags & DM_PARAMS_VMALLOC)
                 vfree(param);
-        else
-                kfree(param);
 }
 
-static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl **param, int *param_flags)
+static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kernel,
+                       int ioctl_flags,
+                       struct dm_ioctl **param, int *param_flags)
 {
-        struct dm_ioctl tmp, *dmi;
+        struct dm_ioctl *dmi;
         int secure_data;
+        const size_t minimum_data_size = sizeof(*param_kernel) - sizeof(param_kernel->data);
 
-        if (copy_from_user(&tmp, user, sizeof(tmp) - sizeof(tmp.data)))
+        if (copy_from_user(param_kernel, user, minimum_data_size))
                 return -EFAULT;
 
-        if (tmp.data_size < (sizeof(tmp) - sizeof(tmp.data)))
+        if (param_kernel->data_size < minimum_data_size)
                 return -EINVAL;
 
-        secure_data = tmp.flags & DM_SECURE_DATA_FLAG;
+        secure_data = param_kernel->flags & DM_SECURE_DATA_FLAG;
 
         *param_flags = secure_data ? DM_WIPE_BUFFER : 0;
 
+        if (ioctl_flags & IOCTL_FLAGS_NO_PARAMS) {
+                dmi = param_kernel;
+                dmi->data_size = minimum_data_size;
+                goto data_copied;
+        }
+
         /*
          * Try to avoid low memory issues when a device is suspended.
          * Use kmalloc() rather than vmalloc() when we can.
          */
         dmi = NULL;
-        if (tmp.data_size <= KMALLOC_MAX_SIZE)
-                dmi = kmalloc(tmp.data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+        if (param_kernel->data_size <= KMALLOC_MAX_SIZE) {
+                dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
+                if (dmi)
+                        *param_flags |= DM_PARAMS_KMALLOC;
+        }
 
         if (!dmi) {
-                dmi = __vmalloc(tmp.data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH, PAGE_KERNEL);
-                *param_flags |= DM_PARAMS_VMALLOC;
+                dmi = __vmalloc(param_kernel->data_size, GFP_NOIO | __GFP_REPEAT | __GFP_HIGH, PAGE_KERNEL);
+                if (dmi)
+                        *param_flags |= DM_PARAMS_VMALLOC;
         }
 
         if (!dmi) {
-                if (secure_data && clear_user(user, tmp.data_size))
+                if (secure_data && clear_user(user, param_kernel->data_size))
                         return -EFAULT;
                 return -ENOMEM;
         }
 
-        if (copy_from_user(dmi, user, tmp.data_size))
+        if (copy_from_user(dmi, user, param_kernel->data_size))
                 goto bad;
 
+data_copied:
         /*
          * Abort if something changed the ioctl data while it was being copied.
          */
-        if (dmi->data_size != tmp.data_size) {
+        if (dmi->data_size != param_kernel->data_size) {
                 DMERR("rejecting ioctl: data size modified while processing parameters");
                 goto bad;
         }
 
         /* Wipe the user buffer so we do not return it to userspace */
-        if (secure_data && clear_user(user, tmp.data_size))
+        if (secure_data && clear_user(user, param_kernel->data_size))
                 goto bad;
 
         *param = dmi;
         return 0;
 
 bad:
-        free_params(dmi, tmp.data_size, *param_flags);
+        free_params(dmi, param_kernel->data_size, *param_flags);
 
         return -EFAULT;
 }
@@ -1671,6 +1686,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
         struct dm_ioctl *uninitialized_var(param);
         ioctl_fn fn = NULL;
         size_t input_param_size;
+        struct dm_ioctl param_kernel;
 
         /* only root can play with this */
         if (!capable(CAP_SYS_ADMIN))
@@ -1704,7 +1720,7 @@ static int ctl_ioctl(uint command, struct dm_ioctl __user *user)
         /*
          * Copy the parameters into kernel space.
          */
-        r = copy_params(user, &param, &param_flags);
+        r = copy_params(user, &param_kernel, ioctl_flags, &param, &param_flags);
 
         if (r)
                 return r;