path: root/ipc
diff options
authorDave Hansen <haveblue@us.ibm.com>2008-02-15 14:37:48 -0800
committerAl Viro <viro@zeniv.linux.org.uk>2008-04-19 00:29:25 -0400
commit4a3fd211ccfc08a88edc824300e25a87785c6a5f (patch)
tree99f1a76a99fa78464b8de731f7fdb5bcc9667a5e /ipc
parent42a74f206b914db13ee1f5ae932dcd91a77c8579 (diff)
[PATCH] r/o bind mounts: elevate write count for open()s
This is the first really tricky patch in the series. It elevates the writer count on a mount each time a non-special file is opened for write. We used to do this in may_open(), but Miklos pointed out that __dentry_open() is used as well to create filps. This will cover even those cases, while a call in may_open() would not have. There is also an elevated count around the vfs_create() call in open_namei(). See the comments for more details, but we need this to fix a 'create, remount, fail r/w open()' race. Some filesystems forego the use of normal vfs calls to create struct files. Make sure that these users elevate the mnt writer count because they will get __fput(), and we need to make sure they're balanced. 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>
Diffstat (limited to 'ipc')
1 files changed, 14 insertions, 2 deletions
diff --git a/ipc/mqueue.c b/ipc/mqueue.c
index 34262c11f48..94fd3b08fb7 100644
--- a/ipc/mqueue.c
+++ b/ipc/mqueue.c
@@ -598,6 +598,7 @@ static struct file *do_create(struct dentry *dir, struct dentry *dentry,
int oflag, mode_t mode, struct mq_attr __user *u_attr)
struct mq_attr attr;
+ struct file *result;
int ret;
if (u_attr) {
@@ -612,13 +613,24 @@ static struct file *do_create(struct dentry *dir, struct dentry *dentry,
mode &= ~current->fs->umask;
+ ret = mnt_want_write(mqueue_mnt);
+ if (ret)
+ goto out;
ret = vfs_create(dir->d_inode, dentry, mode, NULL);
dentry->d_fsdata = NULL;
if (ret)
- goto out;
+ goto out_drop_write;
- return dentry_open(dentry, mqueue_mnt, oflag);
+ result = dentry_open(dentry, mqueue_mnt, oflag);
+ /*
+ * dentry_open() took a persistent mnt_want_write(),
+ * so we can now drop this one.
+ */
+ mnt_drop_write(mqueue_mnt);
+ return result;
+ mnt_drop_write(mqueue_mnt);