[PATCH] r/o bind mounts: elevate write count for ioctls()

Some ioctl()s can cause writes to the filesystem.  Take these, and make them
use mnt_want/drop_write() instead.

[AV: updated]

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 37 insertions, 20 deletions

diff --git a/fs/ext2/ioctl.c b/fs/ext2/ioctl.c
index b8ea11fee5c..de876fa793e 100644
--- a/fs/ext2/ioctl.c
+++ b/fs/ext2/ioctl.c
@@ -12,6 +12,7 @@
 #include <linux/time.h>
 #include <linux/sched.h>
 #include <linux/compat.h>
+#include <linux/mount.h>
 #include <linux/smp_lock.h>
 #include <asm/current.h>
 #include <asm/uaccess.h>
@@ -23,6 +24,7 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
         struct ext2_inode_info *ei = EXT2_I(inode);
         unsigned int flags;
         unsigned short rsv_window_size;
+        int ret;
 
         ext2_debug ("cmd = %u, arg = %lu\n", cmd, arg);
 
@@ -34,14 +36,19 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
         case EXT2_IOC_SETFLAGS: {
                 unsigned int oldflags;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
+                ret = mnt_want_write(filp->f_path.mnt);
+                if (ret)
+                        return ret;
 
-                if (!is_owner_or_cap(inode))
-                        return -EACCES;
+                if (!is_owner_or_cap(inode)) {
+                        ret = -EACCES;
+                        goto setflags_out;
+                }
 
-                if (get_user(flags, (int __user *) arg))
-                        return -EFAULT;
+                if (get_user(flags, (int __user *) arg)) {
+                        ret = -EFAULT;
+                        goto setflags_out;
+                }
 
                 if (!S_ISDIR(inode->i_mode))
                         flags &= ~EXT2_DIRSYNC_FL;
@@ -50,7 +57,8 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                 /* Is it quota file? Do not allow user to mess with it */
                 if (IS_NOQUOTA(inode)) {
                         mutex_unlock(&inode->i_mutex);
-                        return -EPERM;
+                        ret = -EPERM;
+                        goto setflags_out;
                 }
                 oldflags = ei->i_flags;
 
@@ -63,7 +71,8 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                 if ((flags ^ oldflags) & (EXT2_APPEND_FL | EXT2_IMMUTABLE_FL)) {
                         if (!capable(CAP_LINUX_IMMUTABLE)) {
                                 mutex_unlock(&inode->i_mutex);
-                                return -EPERM;
+                                ret = -EPERM;
+                                goto setflags_out;
                         }
                 }
 
@@ -75,20 +84,26 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                 ext2_set_inode_flags(inode);
                 inode->i_ctime = CURRENT_TIME_SEC;
                 mark_inode_dirty(inode);
-                return 0;
+setflags_out:
+                mnt_drop_write(filp->f_path.mnt);
+                return ret;
         }
         case EXT2_IOC_GETVERSION:
                 return put_user(inode->i_generation, (int __user *) arg);
         case EXT2_IOC_SETVERSION:
                 if (!is_owner_or_cap(inode))
                         return -EPERM;
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-                if (get_user(inode->i_generation, (int __user *) arg))
-                        return -EFAULT; 
-                inode->i_ctime = CURRENT_TIME_SEC;
-                mark_inode_dirty(inode);
-                return 0;
+                ret = mnt_want_write(filp->f_path.mnt);
+                if (ret)
+                        return ret;
+                if (get_user(inode->i_generation, (int __user *) arg)) {
+                        ret = -EFAULT;
+                } else {
+                        inode->i_ctime = CURRENT_TIME_SEC;
+                        mark_inode_dirty(inode);
+                }
+                mnt_drop_write(filp->f_path.mnt);
+                return ret;
         case EXT2_IOC_GETRSVSZ:
                 if (test_opt(inode->i_sb, RESERVATION)
                         && S_ISREG(inode->i_mode)
@@ -102,15 +117,16 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                 if (!test_opt(inode->i_sb, RESERVATION) ||!S_ISREG(inode->i_mode))
                         return -ENOTTY;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-
-                if ((current->fsuid != inode->i_uid) && !capable(CAP_FOWNER))
+                if (!is_owner_or_cap(inode))
                         return -EACCES;
 
                 if (get_user(rsv_window_size, (int __user *)arg))
                         return -EFAULT;
 
+                ret = mnt_want_write(filp->f_path.mnt);
+                if (ret)
+                        return ret;
+
                 if (rsv_window_size > EXT2_MAX_RESERVE_BLOCKS)
                         rsv_window_size = EXT2_MAX_RESERVE_BLOCKS;
 
@@ -131,6 +147,7 @@ long ext2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
                         rsv->rsv_goal_size = rsv_window_size;
                 }
                 mutex_unlock(&ei->truncate_mutex);
+                mnt_drop_write(filp->f_path.mnt);
                 return 0;
         }
         default: