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 <viro@zeniv.linux.org.uk>
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 <ydroneaud@opteya.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 8db932d..8ebd9a3 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 @@
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 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_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_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 @@
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 @@
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_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)
