From ede1bf0dcff2b07001c760992b1ca18fd0f419bc Mon Sep 17 00:00:00 2001 From: Yann Droneaud Date: Tue, 30 Jun 2015 14:57:30 -0700 Subject: [PATCH] fs: use seq_open_private() for proc_mounts A patchset to remove support for passing pre-allocated struct seq_file to seq_open(). Such feature is undocumented and prone to error. In particular, if seq_release() is used in release handler, it will kfree() a pointer which was not allocated by seq_open(). So this patchset drops support for pre-allocated struct seq_file: it's only of use in proc_namespace.c and can be easily replaced by using seq_open_private()/seq_release_private(). Additionally, it documents the use of file->private_data to hold pointer to struct seq_file by seq_open(). This patch (of 3): Since patch described below, from v2.6.15-rc1, seq_open() could use a struct seq_file already allocated by the caller if the pointer to the structure is stored in file->private_data before calling the function. Commit 1abe77b0fc4b485927f1f798ae81a752677e1d05 Author: Al Viro Date: Mon Nov 7 17:15:34 2005 -0500 [PATCH] allow callers of seq_open do allocation themselves Allow caller of seq_open() to kmalloc() seq_file + whatever else they want and set ->private_data to it. seq_open() will then abstain from doing allocation itself. Such behavior is only used by mounts_open_common(). In order to drop support for such uncommon feature, proc_mounts is converted to use seq_open_private(), which take care of allocating the proc_mounts structure, making it available through ->private in struct seq_file. Conversely, proc_mounts is converted to use seq_release_private(), in order to release the private structure allocated by seq_open_private(). Then, ->private is used directly instead of proc_mounts() macro to access to the proc_mounts structure. Link: http://lkml.kernel.org/r/cover.1433193673.git.ydroneaud@opteya.com Signed-off-by: Yann Droneaud Cc: Al Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/mount.h | 3 --- fs/namespace.c | 6 +++--- fs/proc_namespace.c | 34 ++++++++++++++++------------------ 3 files changed, 19 insertions(+), 24 deletions(-) diff --git a/fs/mount.h b/fs/mount.h index b5b8082bfa42..14db05d424f7 100644 --- a/fs/mount.h +++ b/fs/mount.h @@ -118,7 +118,6 @@ static inline void unlock_mount_hash(void) } struct proc_mounts { - struct seq_file m; struct mnt_namespace *ns; struct path root; int (*show)(struct seq_file *, struct vfsmount *); @@ -127,8 +126,6 @@ struct proc_mounts { loff_t cached_index; }; -#define proc_mounts(p) (container_of((p), struct proc_mounts, m)) - extern const struct seq_operations mounts_op; extern bool __is_local_mountpoint(struct dentry *dentry); diff --git a/fs/namespace.c b/fs/namespace.c index 9c1c43d0d4f1..e99f1f4e00cd 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1226,7 +1226,7 @@ EXPORT_SYMBOL(replace_mount_options); /* iterator; we want it to have access to namespace_sem, thus here... */ static void *m_start(struct seq_file *m, loff_t *pos) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; down_read(&namespace_sem); if (p->cached_event == p->ns->event) { @@ -1247,7 +1247,7 @@ static void *m_start(struct seq_file *m, loff_t *pos) static void *m_next(struct seq_file *m, void *v, loff_t *pos) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; p->cached_mount = seq_list_next(v, &p->ns->list, pos); p->cached_index = *pos; @@ -1261,7 +1261,7 @@ static void m_stop(struct seq_file *m, void *v) static int m_show(struct seq_file *m, void *v) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; struct mount *r = list_entry(v, struct mount, mnt_list); return p->show(m, &r->mnt); } diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c index 8db932da4009..8ebd9a334085 100644 --- a/fs/proc_namespace.c +++ b/fs/proc_namespace.c @@ -17,7 +17,8 @@ static unsigned mounts_poll(struct file *file, poll_table *wait) { - struct proc_mounts *p = proc_mounts(file->private_data); + struct seq_file *m = file->private_data; + struct proc_mounts *p = m->private; struct mnt_namespace *ns = p->ns; unsigned res = POLLIN | POLLRDNORM; int event; @@ -25,8 +26,8 @@ static unsigned mounts_poll(struct file *file, poll_table *wait) poll_wait(file, &p->ns->poll, wait); event = ACCESS_ONCE(ns->event); - if (p->m.poll_event != event) { - p->m.poll_event = event; + if (m->poll_event != event) { + m->poll_event = event; res |= POLLERR | POLLPRI; } @@ -92,7 +93,7 @@ static void show_type(struct seq_file *m, struct super_block *sb) static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; struct mount *r = real_mount(mnt); int err = 0; struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt }; @@ -126,7 +127,7 @@ static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt) static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; struct mount *r = real_mount(mnt); struct super_block *sb = mnt->mnt_sb; struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt }; @@ -186,7 +187,7 @@ static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt) static int show_vfsstat(struct seq_file *m, struct vfsmount *mnt) { - struct proc_mounts *p = proc_mounts(m); + struct proc_mounts *p = m->private; struct mount *r = real_mount(mnt); struct path mnt_path = { .dentry = mnt->mnt_root, .mnt = mnt }; struct super_block *sb = mnt_path.dentry->d_sb; @@ -236,6 +237,7 @@ static int mounts_open_common(struct inode *inode, struct file *file, struct mnt_namespace *ns = NULL; struct path root; struct proc_mounts *p; + struct seq_file *m; int ret = -EINVAL; if (!task) @@ -260,26 +262,21 @@ static int mounts_open_common(struct inode *inode, struct file *file, task_unlock(task); put_task_struct(task); - ret = -ENOMEM; - p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL); - if (!p) + ret = seq_open_private(file, &mounts_op, sizeof(struct proc_mounts)); + if (ret) goto err_put_path; - file->private_data = &p->m; - ret = seq_open(file, &mounts_op); - if (ret) - goto err_free; + m = file->private_data; + m->poll_event = ns->event; + p = m->private; p->ns = ns; p->root = root; - p->m.poll_event = ns->event; p->show = show; p->cached_event = ~0ULL; return 0; - err_free: - kfree(p); err_put_path: path_put(&root); err_put_ns: @@ -290,10 +287,11 @@ static int mounts_open_common(struct inode *inode, struct file *file, static int mounts_release(struct inode *inode, struct file *file) { - struct proc_mounts *p = proc_mounts(file->private_data); + struct seq_file *m = file->private_data; + struct proc_mounts *p = m->private; path_put(&p->root); put_mnt_ns(p->ns); - return seq_release(inode, file); + return seq_release_private(inode, file); } static int mounts_open(struct inode *inode, struct file *file)