[PATCH] proc: Close the race of a process dying durning lookup
proc_lookup and task exiting are not synchronized, although some of the
previous code may have suggested that. Every time before we reuse a dentry
namei.c calls d_op->derevalidate which prevents us from reusing a stale dcache
entry. Unfortunately it does not prevent us from returning a stale dcache
entry. This race has been explicitly plugged in proc_pid_lookup but there is
nothing to confine it to just that proc lookup function.
So to prevent the race I call revalidate explictily in all of the proc lookup
functions after I call d_add, and report an error if the revalidate does not
succeed.
Years ago Al Viro did something similar but those changes got lost in the
churn.
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f435932..98eaeaa 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1402,6 +1402,7 @@
{
struct task_struct *task = proc_task(dir);
unsigned fd = name_to_int(dentry);
+ struct dentry *result = ERR_PTR(-ENOENT);
struct file * file;
struct files_struct * files;
struct inode *inode;
@@ -1441,15 +1442,18 @@
ei->op.proc_get_link = proc_fd_link;
dentry->d_op = &tid_fd_dentry_operations;
d_add(dentry, inode);
- return NULL;
+ /* Close the race of the process dying before we return the dentry */
+ if (tid_fd_revalidate(dentry, NULL))
+ result = NULL;
+out:
+ return result;
out_unlock2:
spin_unlock(&files->file_lock);
put_files_struct(files);
out_unlock:
iput(inode);
-out:
- return ERR_PTR(-ENOENT);
+ goto out;
}
static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldir);
@@ -1549,12 +1553,12 @@
struct pid_entry *ents)
{
struct inode *inode;
- int error;
+ struct dentry *error;
struct task_struct *task = proc_task(dir);
struct pid_entry *p;
struct proc_inode *ei;
- error = -ENOENT;
+ error = ERR_PTR(-ENOENT);
inode = NULL;
if (!pid_alive(task))
@@ -1569,7 +1573,7 @@
if (!p->name)
goto out;
- error = -EINVAL;
+ error = ERR_PTR(-EINVAL);
inode = proc_pid_make_inode(dir->i_sb, task, p->type);
if (!inode)
goto out;
@@ -1736,14 +1740,16 @@
default:
printk("procfs: impossible type (%d)",p->type);
iput(inode);
- return ERR_PTR(-EINVAL);
+ error = ERR_PTR(-EINVAL);
+ goto out;
}
dentry->d_op = &pid_dentry_operations;
d_add(dentry, inode);
- return NULL;
-
+ /* Close the race of the process dying before we return the dentry */
+ if (pid_revalidate(dentry, NULL))
+ error = NULL;
out:
- return ERR_PTR(error);
+ return error;
}
static struct dentry *proc_tgid_base_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd){
@@ -1911,6 +1917,7 @@
/* SMP-safe */
struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *nd)
{
+ struct dentry *result = ERR_PTR(-ENOENT);
struct task_struct *task;
struct inode *inode;
struct proc_inode *ei;
@@ -1944,12 +1951,9 @@
goto out;
inode = proc_pid_make_inode(dir->i_sb, task, PROC_TGID_INO);
+ if (!inode)
+ goto out_put_task;
-
- if (!inode) {
- put_task_struct(task);
- goto out;
- }
inode->i_mode = S_IFDIR|S_IRUGO|S_IXUGO;
inode->i_op = &proc_tgid_base_inode_operations;
inode->i_fop = &proc_tgid_base_operations;
@@ -1963,21 +1967,20 @@
dentry->d_op = &pid_dentry_operations;
d_add(dentry, inode);
- if (!pid_alive(task)) {
- d_drop(dentry);
- shrink_dcache_parent(dentry);
- goto out;
- }
+ /* Close the race of the process dying before we return the dentry */
+ if (pid_revalidate(dentry, NULL))
+ result = NULL;
+out_put_task:
put_task_struct(task);
- return NULL;
out:
- return ERR_PTR(-ENOENT);
+ return result;
}
/* SMP-safe */
static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *nd)
{
+ struct dentry *result = ERR_PTR(-ENOENT);
struct task_struct *task;
struct task_struct *leader = proc_task(dir);
struct inode *inode;
@@ -2015,13 +2018,14 @@
dentry->d_op = &pid_dentry_operations;
d_add(dentry, inode);
+ /* Close the race of the process dying before we return the dentry */
+ if (pid_revalidate(dentry, NULL))
+ result = NULL;
- put_task_struct(task);
- return NULL;
out_drop_task:
put_task_struct(task);
out:
- return ERR_PTR(-ENOENT);
+ return result;
}
#define PROC_NUMBUF 10