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

Now includes fix for oops seen by akpm.

"never let a libc developer write your kernel code" - hch

"nor, apparently, a kernel developer" - akpm

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Cc: Valdis Kletnieks <Valdis.Kletnieks@vt.edu>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 6 deletions

diff --git a/fs/utimes.c b/fs/utimes.c
index b18da9c0b97f..a2bef77dc9c9 100644
--- a/fs/utimes.c
+++ b/fs/utimes.c
@@ -2,6 +2,7 @@
 #include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/linkage.h>
+#include <linux/mount.h>
 #include <linux/namei.h>
 #include <linux/sched.h>
 #include <linux/stat.h>
@@ -59,6 +60,7 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
         struct inode *inode;
         struct iattr newattrs;
         struct file *f = NULL;
+        struct vfsmount *mnt;
 
         error = -EINVAL;
         if (times && (!nsec_valid(times[0].tv_nsec) ||
@@ -79,18 +81,20 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
                 if (!f)
                         goto out;
                 dentry = f->f_path.dentry;
+                mnt = f->f_path.mnt;
         } else {
                 error = __user_walk_fd(dfd, filename, (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW, &nd);
                 if (error)
                         goto out;
 
                 dentry = nd.path.dentry;
+                mnt = nd.path.mnt;
         }
 
         inode = dentry->d_inode;
 
-        error = -EROFS;
-        if (IS_RDONLY(inode))
+        error = mnt_want_write(mnt);
+        if (error)
                 goto dput_and_out;
 
         /* Don't worry, the checks are done in inode_change_ok() */
@@ -98,7 +102,7 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
         if (times) {
                 error = -EPERM;
                 if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
-                        goto dput_and_out;
+                        goto mnt_drop_write_and_out;
 
                 if (times[0].tv_nsec == UTIME_OMIT)
                         newattrs.ia_valid &= ~ATTR_ATIME;
@@ -118,22 +122,24 @@ long do_utimes(int dfd, char __user *filename, struct timespec *times, int flags
         } else {
                 error = -EACCES;
                 if (IS_IMMUTABLE(inode))
-                        goto dput_and_out;
+                        goto mnt_drop_write_and_out;
 
                 if (!is_owner_or_cap(inode)) {
                         if (f) {
                                 if (!(f->f_mode & FMODE_WRITE))
-                                        goto dput_and_out;
+                                        goto mnt_drop_write_and_out;
                         } else {
                                 error = vfs_permission(&nd, MAY_WRITE);
                                 if (error)
-                                        goto dput_and_out;
+                                        goto mnt_drop_write_and_out;
                         }
                 }
         }
         mutex_lock(&inode->i_mutex);
         error = notify_change(dentry, &newattrs);
         mutex_unlock(&inode->i_mutex);
+mnt_drop_write_and_out:
+        mnt_drop_write(mnt);
 dput_and_out:
         if (f)
                 fput(f);