commit 6fc23c00b896aaa621ea36b00035e6f8e74e58c8
Author: Erez Zadok <[EMAIL PROTECTED]>
Date: Thu Sep 18 23:00:23 2008 -0400
Unionfs: fix readlink/follow_link to add locking
Signed-off-by: Erez Zadok <[EMAIL PROTECTED]>
diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
index 62311d2..296803c 100644
--- a/fs/unionfs/inode.c
+++ b/fs/unionfs/inode.c
@@ -637,21 +637,12 @@ out:
return err;
}
-static int unionfs_readlink(struct dentry *dentry, char __user *buf,
- int bufsiz)
+/* requires sb, dentry, and parent to already be locked */
+static int __unionfs_readlink(struct dentry *dentry, char __user *buf,
+ int bufsiz)
{
int err;
struct dentry *lower_dentry;
- struct dentry *parent;
-
- unionfs_read_lock(dentry->d_sb, UNIONFS_SMUTEX_CHILD);
- parent = unionfs_lock_parent(dentry, UNIONFS_DMUTEX_PARENT);
- unionfs_lock_dentry(dentry, UNIONFS_DMUTEX_CHILD);
-
- if (unlikely(!__unionfs_d_revalidate(dentry, parent, NULL, false))) {
- err = -ESTALE;
- goto out;
- }
lower_dentry = unionfs_lower_dentry(dentry);
@@ -663,11 +654,32 @@ static int unionfs_readlink(struct dentry *dentry, char
__user *buf,
err = lower_dentry->d_inode->i_op->readlink(lower_dentry,
buf, bufsiz);
- if (err > 0)
+ if (err >= 0)
fsstack_copy_attr_atime(dentry->d_inode,
lower_dentry->d_inode);
out:
+ return err;
+}
+
+static int unionfs_readlink(struct dentry *dentry, char __user *buf,
+ int bufsiz)
+{
+ int err;
+ struct dentry *parent;
+
+ unionfs_read_lock(dentry->d_sb, UNIONFS_SMUTEX_CHILD);
+ parent = unionfs_lock_parent(dentry, UNIONFS_DMUTEX_PARENT);
+ unionfs_lock_dentry(dentry, UNIONFS_DMUTEX_CHILD);
+
+ if (unlikely(!__unionfs_d_revalidate(dentry, parent, NULL, false))) {
+ err = -ESTALE;
+ goto out;
+ }
+
+ err = __unionfs_readlink(dentry, buf, bufsiz);
+
+out:
unionfs_check_dentry(dentry);
unionfs_unlock_dentry(dentry);
unionfs_unlock_parent(dentry, parent);
@@ -676,22 +688,16 @@ out:
return err;
}
-/*
- * unionfs_follow_link takes a dentry, but it is simple. It only needs to
- * allocate some memory and then call our ->readlink method. Our
- * unionfs_readlink *does* lock our dentry and revalidate the dentry.
- * Therefore, we do not have to lock our dentry here, to prevent a deadlock;
- * nor do we need to revalidate it either. It is safe to not lock our
- * dentry here, nor revalidate it, because unionfs_follow_link does not do
- * anything (prior to calling ->readlink) which could become inconsistent
- * due to branch management. We also don't need to lock our super because
- * this function isn't affected by branch-management.
- */
static void *unionfs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
char *buf;
int len = PAGE_SIZE, err;
mm_segment_t old_fs;
+ struct dentry *parent;
+
+ unionfs_read_lock(dentry->d_sb, UNIONFS_SMUTEX_CHILD);
+ parent = unionfs_lock_parent(dentry, UNIONFS_DMUTEX_PARENT);
+ unionfs_lock_dentry(dentry, UNIONFS_DMUTEX_CHILD);
/* This is freed by the put_link method assuming a successful call. */
buf = kmalloc(len, GFP_KERNEL);
@@ -703,7 +709,7 @@ static void *unionfs_follow_link(struct dentry *dentry,
struct nameidata *nd)
/* read the symlink, and then we will follow it */
old_fs = get_fs();
set_fs(KERNEL_DS);
- err = dentry->d_inode->i_op->readlink(dentry, (char __user *)buf, len);
+ err = __unionfs_readlink(dentry, buf, len);
set_fs(old_fs);
if (err < 0) {
kfree(buf);
@@ -715,12 +721,15 @@ static void *unionfs_follow_link(struct dentry *dentry,
struct nameidata *nd)
err = 0;
out:
- if (!err) {
- unionfs_lock_dentry(dentry, UNIONFS_DMUTEX_CHILD);
+ if (err >= 0) {
+ unionfs_check_nd(nd);
unionfs_check_dentry(dentry);
- unionfs_unlock_dentry(dentry);
}
- unionfs_check_nd(nd);
+
+ unionfs_unlock_dentry(dentry);
+ unionfs_unlock_parent(dentry, parent);
+ unionfs_read_unlock(dentry->d_sb);
+
return ERR_PTR(err);
}
_______________________________________________
unionfs-cvs mailing list: http://unionfs.filesystems.org/
[email protected]
http://www.fsl.cs.sunysb.edu/mailman/listinfo/unionfs-cvs
