[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, 49 insertions, 37 deletions

diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
index 2ed7c37f897..25b13ede808 100644
--- a/fs/ext4/ioctl.c
+++ b/fs/ext4/ioctl.c
@@ -15,6 +15,7 @@
 #include <linux/time.h>
 #include <linux/compat.h>
 #include <linux/smp_lock.h>
+#include <linux/mount.h>
 #include <asm/uaccess.h>
 
 int ext4_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
@@ -38,24 +39,25 @@ int ext4_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
                 unsigned int oldflags;
                 unsigned int jflag;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-
                 if (!is_owner_or_cap(inode))
                         return -EACCES;
 
                 if (get_user(flags, (int __user *) arg))
                         return -EFAULT;
 
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        return err;
+
                 if (!S_ISDIR(inode->i_mode))
                         flags &= ~EXT4_DIRSYNC_FL;
 
+                err = -EPERM;
                 mutex_lock(&inode->i_mutex);
                 /* Is it quota file? Do not allow user to mess with it */
-                if (IS_NOQUOTA(inode)) {
-                        mutex_unlock(&inode->i_mutex);
-                        return -EPERM;
-                }
+                if (IS_NOQUOTA(inode))
+                        goto flags_out;
+
                 oldflags = ei->i_flags;
 
                 /* The JOURNAL_DATA flag is modifiable only by root */
@@ -68,10 +70,8 @@ int ext4_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
                  * This test looks nicer. Thanks to Pauline Middelink
                  */
                 if ((flags ^ oldflags) & (EXT4_APPEND_FL | EXT4_IMMUTABLE_FL)) {
-                        if (!capable(CAP_LINUX_IMMUTABLE)) {
-                                mutex_unlock(&inode->i_mutex);
-                                return -EPERM;
-                        }
+                        if (!capable(CAP_LINUX_IMMUTABLE))
+                                goto flags_out;
                 }
 
                 /*
@@ -79,17 +79,14 @@ int ext4_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
                  * the relevant capability.
                  */
                 if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL)) {
-                        if (!capable(CAP_SYS_RESOURCE)) {
-                                mutex_unlock(&inode->i_mutex);
-                                return -EPERM;
-                        }
+                        if (!capable(CAP_SYS_RESOURCE))
+                                goto flags_out;
                 }
 
-
                 handle = ext4_journal_start(inode, 1);
                 if (IS_ERR(handle)) {
-                        mutex_unlock(&inode->i_mutex);
-                        return PTR_ERR(handle);
+                        err = PTR_ERR(handle);
+                        goto flags_out;
                 }
                 if (IS_SYNC(inode))
                         handle->h_sync = 1;
@@ -107,14 +104,14 @@ int ext4_ioctl (struct inode * inode, struct file * filp, unsigned int cmd,
                 err = ext4_mark_iloc_dirty(handle, inode, &iloc);
 flags_err:
                 ext4_journal_stop(handle);
-                if (err) {
-                        mutex_unlock(&inode->i_mutex);
-                        return err;
-                }
+                if (err)
+                        goto flags_out;
 
                 if ((jflag ^ oldflags) & (EXT4_JOURNAL_DATA_FL))
                         err = ext4_change_inode_journal_flag(inode, jflag);
+flags_out:
                 mutex_unlock(&inode->i_mutex);
+                mnt_drop_write(filp->f_path.mnt);
                 return err;
         }
         case EXT4_IOC_GETVERSION:
@@ -129,14 +126,20 @@ flags_err:
 
                 if (!is_owner_or_cap(inode))
                         return -EPERM;
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-                if (get_user(generation, (int __user *) arg))
-                        return -EFAULT;
+
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        return err;
+                if (get_user(generation, (int __user *) arg)) {
+                        err = -EFAULT;
+                        goto setversion_out;
+                }
 
                 handle = ext4_journal_start(inode, 1);
-                if (IS_ERR(handle))
-                        return PTR_ERR(handle);
+                if (IS_ERR(handle)) {
+                        err = PTR_ERR(handle);
+                        goto setversion_out;
+                }
                 err = ext4_reserve_inode_write(handle, inode, &iloc);
                 if (err == 0) {
                         inode->i_ctime = ext4_current_time(inode);
@@ -144,6 +147,8 @@ flags_err:
                         err = ext4_mark_iloc_dirty(handle, inode, &iloc);
                 }
                 ext4_journal_stop(handle);
+setversion_out:
+                mnt_drop_write(filp->f_path.mnt);
                 return err;
         }
 #ifdef CONFIG_JBD2_DEBUG
@@ -179,19 +184,21 @@ flags_err:
                 }
                 return -ENOTTY;
         case EXT4_IOC_SETRSVSZ: {
+                int err;
 
                 if (!test_opt(inode->i_sb, RESERVATION) ||!S_ISREG(inode->i_mode))
                         return -ENOTTY;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-
                 if (!is_owner_or_cap(inode))
                         return -EACCES;
 
                 if (get_user(rsv_window_size, (int __user *)arg))
                         return -EFAULT;
 
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        return err;
+
                 if (rsv_window_size > EXT4_MAX_RESERVE_BLOCKS)
                         rsv_window_size = EXT4_MAX_RESERVE_BLOCKS;
 
@@ -208,6 +215,7 @@ flags_err:
                         rsv->rsv_goal_size = rsv_window_size;
                 }
                 up_write(&ei->i_data_sem);
+                mnt_drop_write(filp->f_path.mnt);
                 return 0;
         }
         case EXT4_IOC_GROUP_EXTEND: {
@@ -218,16 +226,18 @@ flags_err:
                 if (!capable(CAP_SYS_RESOURCE))
                         return -EPERM;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-
                 if (get_user(n_blocks_count, (__u32 __user *)arg))
                         return -EFAULT;
 
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        return err;
+
                 err = ext4_group_extend(sb, EXT4_SB(sb)->s_es, n_blocks_count);
                 jbd2_journal_lock_updates(EXT4_SB(sb)->s_journal);
                 jbd2_journal_flush(EXT4_SB(sb)->s_journal);
                 jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
+                mnt_drop_write(filp->f_path.mnt);
 
                 return err;
         }
@@ -239,17 +249,19 @@ flags_err:
                 if (!capable(CAP_SYS_RESOURCE))
                         return -EPERM;
 
-                if (IS_RDONLY(inode))
-                        return -EROFS;
-
                 if (copy_from_user(&input, (struct ext4_new_group_input __user *)arg,
                                 sizeof(input)))
                         return -EFAULT;
 
+                err = mnt_want_write(filp->f_path.mnt);
+                if (err)
+                        return err;
+
                 err = ext4_group_add(sb, &input);
                 jbd2_journal_lock_updates(EXT4_SB(sb)->s_journal);
                 jbd2_journal_flush(EXT4_SB(sb)->s_journal);
                 jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
+                mnt_drop_write(filp->f_path.mnt);
 
                 return err;
         }