From 12487f3067d8d68a90dd2fc0dbc2a287ae699236 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Wed, 26 Feb 2020 14:59:56 -0500 Subject: [PATCH] follow_dotdot{,_rcu}(): massage loops The logics in both of them is the same: while true if in process' root // uncommon break if *not* in mount root // normal case find the parent return if at absolute root // very uncommon break move to underlying mountpoint report that we are in root Pull the common path out of the loop: if in process' root // uncommon goto in_root if unlikely(in mount root) while true if at absolute root goto in_root move to underlying mountpoint if in process' root goto in_root if in mount root break; find the parent // we are not in mount root return in_root: report that we are in root The reason for that transformation is that we get to keep the common path straight *and* get a separate block for "move through underlying mountpoints", which will allow to sanitize NO_XDEV handling there. What's more, the pared-down loops will be easier to deal with - in particular, non-RCU case has no need to grab mount_lock and rewriting it to the form that wouldn't do that is a non-trivial change. Better do that with less stuff getting in the way... Signed-off-by: Al Viro --- fs/namei.c | 77 ++++++++++++++++++++++++++++++++++++-------------------------- 1 file changed, 45 insertions(+), 32 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index fda239b..8cfbd5f 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -1691,21 +1691,12 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, struct inode **inodep, unsigned *seqp) { - while (1) { - if (path_equal(&nd->path, &nd->root)) - break; - if (nd->path.dentry != nd->path.mnt->mnt_root) { - struct dentry *old = nd->path.dentry; - struct dentry *parent = old->d_parent; + struct dentry *parent, *old; - *inodep = parent->d_inode; - *seqp = read_seqcount_begin(&parent->d_seq); - if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq))) - return ERR_PTR(-ECHILD); - if (unlikely(!path_connected(nd->path.mnt, parent))) - return ERR_PTR(-ECHILD); - return parent; - } else { + if (path_equal(&nd->path, &nd->root)) + goto in_root; + if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) { + while (1) { struct mount *mnt = real_mount(nd->path.mnt); struct mount *mparent = mnt->mnt_parent; struct dentry *mountpoint = mnt->mnt_mountpoint; @@ -1714,7 +1705,7 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, if (unlikely(read_seqretry(&mount_lock, nd->m_seq))) return ERR_PTR(-ECHILD); if (&mparent->mnt == nd->path.mnt) - break; + goto in_root; if (unlikely(nd->flags & LOOKUP_NO_XDEV)) return ERR_PTR(-ECHILD); /* we know that mountpoint was pinned */ @@ -1722,8 +1713,22 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, nd->path.mnt = &mparent->mnt; nd->inode = inode; nd->seq = seq; + if (path_equal(&nd->path, &nd->root)) + goto in_root; + if (nd->path.dentry != nd->path.mnt->mnt_root) + break; } } + old = nd->path.dentry; + parent = old->d_parent; + *inodep = parent->d_inode; + *seqp = read_seqcount_begin(&parent->d_seq); + if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq))) + return ERR_PTR(-ECHILD); + if (unlikely(!path_connected(nd->path.mnt, parent))) + return ERR_PTR(-ECHILD); + return parent; +in_root: if (unlikely(nd->flags & LOOKUP_BENEATH)) return ERR_PTR(-ECHILD); return NULL; @@ -1733,25 +1738,33 @@ static struct dentry *follow_dotdot(struct nameidata *nd, struct inode **inodep, unsigned *seqp) { - while (1) { - if (path_equal(&nd->path, &nd->root)) - break; - if (nd->path.dentry != nd->path.mnt->mnt_root) { - /* rare case of legitimate dget_parent()... */ - struct dentry *parent = dget_parent(nd->path.dentry); - if (unlikely(!path_connected(nd->path.mnt, parent))) { - dput(parent); - return ERR_PTR(-ENOENT); - } - *seqp = 0; - *inodep = parent->d_inode; - return parent; + struct dentry *parent; + + if (path_equal(&nd->path, &nd->root)) + goto in_root; + if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) { + while (1) { + if (!follow_up(&nd->path)) + goto in_root; + if (unlikely(nd->flags & LOOKUP_NO_XDEV)) + return ERR_PTR(-EXDEV); + if (path_equal(&nd->path, &nd->root)) + goto in_root; + if (nd->path.dentry != nd->path.mnt->mnt_root) + break; } - if (!follow_up(&nd->path)) - break; - if (unlikely(nd->flags & LOOKUP_NO_XDEV)) - return ERR_PTR(-EXDEV); } + /* rare case of legitimate dget_parent()... */ + parent = dget_parent(nd->path.dentry); + if (unlikely(!path_connected(nd->path.mnt, parent))) { + dput(parent); + return ERR_PTR(-ENOENT); + } + *seqp = 0; + *inodep = parent->d_inode; + return parent; + +in_root: if (unlikely(nd->flags & LOOKUP_BENEATH)) return ERR_PTR(-EXDEV); dget(nd->path.dentry); -- 2.7.4