From bcda76524cd1fa32af748536f27f674a13e56700 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sun, 13 Mar 2011 16:42:14 -0400 Subject: Allow O_PATH for symlinks At that point we can't do almost nothing with them. They can be opened with O_PATH, we can manipulate such descriptors with dup(), etc. and we can see them in /proc/*/{fd,fdinfo}/*. We can't (and won't be able to) follow /proc/*/fd/* symlinks for those; there's simply not enough information for pathname resolution to go on from such point - to resolve a symlink we need to know which directory does it live in. We will be able to do useful things with them after the next commit, though - readlinkat() and fchownat() will be possible to use with dfd being an O_PATH-opened symlink and empty relative pathname. Combined with open_by_handle() it'll give us a way to do realink-by-handle and lchown-by-handle without messing with more redundant syscalls. Signed-off-by: Al Viro --- fs/namei.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) (limited to 'fs') diff --git a/fs/namei.c b/fs/namei.c index e1d9f90d9776..9d4f32700179 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -766,8 +766,14 @@ __do_follow_link(const struct path *link, struct nameidata *nd, void **p) error = 0; if (s) error = __vfs_follow_link(nd, s); - else if (nd->last_type == LAST_BIND) + else if (nd->last_type == LAST_BIND) { nd->flags |= LOOKUP_JUMPED; + if (nd->path.dentry->d_inode->i_op->follow_link) { + /* stepped on a _really_ weird one */ + path_put(&nd->path); + error = -ELOOP; + } + } } return error; } @@ -1954,6 +1960,10 @@ static int may_open(struct path *path, int acc_mode, int flag) struct inode *inode = dentry->d_inode; int error; + /* O_PATH? */ + if (!acc_mode) + return 0; + if (!inode) return -ENOENT; @@ -2056,7 +2066,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, int open_flag = op->open_flag; int will_truncate = open_flag & O_TRUNC; int want_write = 0; - int skip_perm = 0; + int acc_mode = op->acc_mode; struct file *filp; struct inode *inode; int error; @@ -2095,8 +2105,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path, } if (!(open_flag & O_CREAT)) { + int symlink_ok = 0; if (nd->last.name[nd->last.len]) nd->flags |= LOOKUP_FOLLOW | LOOKUP_DIRECTORY; + if (open_flag & O_PATH && !(nd->flags & LOOKUP_FOLLOW)) + symlink_ok = 1; /* we _can_ be in RCU mode here */ error = do_lookup(nd, &nd->last, path, &inode); if (error) { @@ -2108,7 +2121,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, terminate_walk(nd); return ERR_PTR(-ENOENT); } - if (unlikely(inode->i_op->follow_link)) { + if (unlikely(inode->i_op->follow_link && !symlink_ok)) { /* We drop rcu-walk here */ if (nameidata_dentry_drop_rcu_maybe(nd, path->dentry)) return ERR_PTR(-ECHILD); @@ -2175,7 +2188,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path, /* Don't check for write permission, don't truncate */ open_flag &= ~O_TRUNC; will_truncate = 0; - skip_perm = 1; + acc_mode = MAY_OPEN; error = security_path_mknod(&nd->path, dentry, mode, 0); if (error) goto exit_mutex_unlock; @@ -2225,7 +2238,7 @@ ok: want_write = 1; } common: - error = may_open(&nd->path, skip_perm ? 0 : op->acc_mode, open_flag); + error = may_open(&nd->path, acc_mode, open_flag); if (error) goto exit; filp = nameidata_to_filp(nd); @@ -2358,7 +2371,7 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt, flags |= LOOKUP_ROOT; - if (dentry->d_inode->i_op->follow_link) + if (dentry->d_inode->i_op->follow_link && op->intent & LOOKUP_OPEN) return ERR_PTR(-ELOOP); file = path_openat(-1, name, &nd, op, flags | LOOKUP_RCU); -- cgit v1.2.1