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procfs: get rid of ancient BS in pid_revalidate() uses

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First of all, calling pid_revalidate() in the end of <pid>/* lookups
is *not* about closing any kind of races; that used to be true once
upon a time, but these days those comments are actively misleading.
Especially since pid_revalidate() doesn't even do d_drop() on
failure anymore.  It doesn't matter, anyway, since once
pid_revalidate() starts returning false, ->d_delete() of those
dentries starts saying "don't keep"; they won't get stuck in
dcache any longer than they are pinned.

These calls cannot be just removed, though - the side effect of
pid_revalidate() (updating i_uid/i_gid/etc.) is what we are calling
it for here.

Let's separate the "update ownership" into a new helper (pid_update_inode())
and use it, both in lookups and in pid_revalidate() itself.

The comments in pid_revalidate() are also out of date - they refer to
the time when pid_revalidate() used to call d_drop() directly...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Al Viro 2018-05-02 21:26:16 -04:00
parent 11f17c9bd7
commit 1bbc55131e
3 changed files with 28 additions and 38 deletions
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55
fs/proc/base.c
View File

@ -1803,15 +1803,22 @@ int pid_getattr(const struct path *path, struct kstat *stat,
/* dentry stuff */
/*
* Exceptional case: normally we are not allowed to unhash a busy
* directory. In this case, however, we can do it - no aliasing problems
* due to the way we treat inodes.
*
* Set <pid>/... inode ownership (can change due to setuid(), etc.)
*/
void pid_update_inode(struct task_struct *task, struct inode *inode)
{
task_dump_owner(task, inode->i_mode, &inode->i_uid, &inode->i_gid);
inode->i_mode &= ~(S_ISUID | S_ISGID);
security_task_to_inode(task, inode);
}
/*
* Rewrite the inode's ownerships here because the owning task may have
* performed a setuid(), etc.
*
*/
int pid_revalidate(struct dentry *dentry, unsigned int flags)
static int pid_revalidate(struct dentry *dentry, unsigned int flags)
{
struct inode *inode;
struct task_struct *task;
@ -1823,10 +1830,7 @@ int pid_revalidate(struct dentry *dentry, unsigned int flags)
task = get_proc_task(inode);
if (task) {
task_dump_owner(task, inode->i_mode, &inode->i_uid, &inode->i_gid);
inode->i_mode &= ~(S_ISUID | S_ISGID);
security_task_to_inode(task, inode);
pid_update_inode(task, inode);
put_task_struct(task);
return 1;
}
@ -2438,7 +2442,7 @@ static int proc_pident_instantiate(struct inode *dir,
inode = proc_pid_make_inode(dir->i_sb, task, p->mode);
if (!inode)
goto out;
return -ENOENT;
ei = PROC_I(inode);
if (S_ISDIR(inode->i_mode))
@ -2448,13 +2452,10 @@ static int proc_pident_instantiate(struct inode *dir,
if (p->fop)
inode->i_fop = p->fop;
ei->op = p->op;
pid_update_inode(task, inode);
d_set_d_op(dentry, &pid_dentry_operations);
d_add(dentry, inode);
/* Close the race of the process dying before we return the dentry */
if (pid_revalidate(dentry, 0))
return 0;
out:
return -ENOENT;
return 0;
}
static struct dentry *proc_pident_lookup(struct inode *dir,
@ -3140,22 +3141,18 @@ static int proc_pid_instantiate(struct inode *dir,
inode = proc_pid_make_inode(dir->i_sb, task, S_IFDIR | S_IRUGO | S_IXUGO);
if (!inode)
goto out;
return -ENOENT;
inode->i_op = &proc_tgid_base_inode_operations;
inode->i_fop = &proc_tgid_base_operations;
inode->i_flags|=S_IMMUTABLE;
set_nlink(inode, nlink_tgid);
pid_update_inode(task, inode);
d_set_d_op(dentry, &pid_dentry_operations);
d_add(dentry, inode);
/* Close the race of the process dying before we return the dentry */
if (pid_revalidate(dentry, 0))
return 0;
out:
return -ENOENT;
return 0;
}
struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsigned int flags)
@ -3434,23 +3431,19 @@ static int proc_task_instantiate(struct inode *dir,
{
struct inode *inode;
inode = proc_pid_make_inode(dir->i_sb, task, S_IFDIR | S_IRUGO | S_IXUGO);
if (!inode)
goto out;
return -ENOENT;
inode->i_op = &proc_tid_base_inode_operations;
inode->i_fop = &proc_tid_base_operations;
inode->i_flags|=S_IMMUTABLE;
inode->i_flags |= S_IMMUTABLE;
set_nlink(inode, nlink_tid);
pid_update_inode(task, inode);
d_set_d_op(dentry, &pid_dentry_operations);
d_add(dentry, inode);
/* Close the race of the process dying before we return the dentry */
if (pid_revalidate(dentry, 0))
return 0;
out:
return -ENOENT;
return 0;
}
static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry, unsigned int flags)

2
fs/proc/internal.h
View File

@ -147,7 +147,7 @@ extern const struct dentry_operations pid_dentry_operations;
extern int pid_getattr(const struct path *, struct kstat *, u32, unsigned int);
extern int proc_setattr(struct dentry *, struct iattr *);
extern struct inode *proc_pid_make_inode(struct super_block *, struct task_struct *, umode_t);
extern int pid_revalidate(struct dentry *, unsigned int);
extern void pid_update_inode(struct task_struct *, struct inode *);
extern int pid_delete_dentry(const struct dentry *);
extern int proc_pid_readdir(struct file *, struct dir_context *);
extern struct dentry *proc_pid_lookup(struct inode *, struct dentry *, unsigned int);

9
fs/proc/namespaces.c
View File

@ -96,19 +96,16 @@ static int proc_ns_instantiate(struct inode *dir,
inode = proc_pid_make_inode(dir->i_sb, task, S_IFLNK | S_IRWXUGO);
if (!inode)
goto out;
return -ENOENT;
ei = PROC_I(inode);
inode->i_op = &proc_ns_link_inode_operations;
ei->ns_ops = ns_ops;
pid_update_inode(task, inode);
d_set_d_op(dentry, &pid_dentry_operations);
d_add(dentry, inode);
/* Close the race of the process dying before we return the dentry */
if (pid_revalidate(dentry, 0))
return 0;
out:
return -ENOENT;
return 0;
}
static int proc_ns_dir_readdir(struct file *file, struct dir_context *ctx)