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 <[email protected]>
---
fs/proc/base.c | 54 +++++++++++++++++++++++++++++-------------------------
1 files changed, 29 insertions(+), 25 deletions(-)
aea0459c7bef967ce3345449db5183d4b2dafefe
diff --git a/fs/proc/base.c b/fs/proc/base.c
index 9fab7fe..36cddda 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -1340,6 +1340,7 @@ static struct dentry *proc_lookupfd(stru
{
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;
@@ -1374,15 +1375,18 @@ static struct dentry *proc_lookupfd(stru
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:
rcu_read_unlock();
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);
@@ -1482,12 +1486,12 @@ static struct dentry *proc_pident_lookup
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))
@@ -1502,7 +1506,7 @@ static struct dentry *proc_pident_lookup
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;
@@ -1663,14 +1667,16 @@ static struct dentry *proc_pident_lookup
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){
@@ -1846,6 +1852,7 @@ out:
/* 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;
@@ -1879,12 +1886,9 @@ struct dentry *proc_pid_lookup(struct in
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;
@@ -1898,21 +1902,20 @@ struct dentry *proc_pid_lookup(struct in
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;
@@ -1950,13 +1953,14 @@ static struct dentry *proc_task_lookup(s
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
--
1.2.2.g709a
-
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