[PATCH 5/6] proc: use task_access_lock() instead of ptrace_may_access()

Cong Wang
2012-04-11T06:01:39Z

There are several places in fs/proc/base.c still use ptrace_may_access()
directly to check the permission, actually this just gets a snapshot of
the permission, nothing prevents the target task from raising the priviledges
itself, it is better to use task_access_lock() for these places, to hold
the priviledges.

Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
---
fs/proc/base.c | 74 +++++++++++++++++++++++++-------------------------------
1 files changed, 33 insertions(+), 41 deletions(-)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index f1d18fc..2dff86b 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -253,6 +253,23 @@ static int proc_pid_auxv(struct task_struct *task, char *buffer)
return res;
}

+static int task_access_lock(struct task_struct *task, unsigned int mode)
+
+{
+ int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
+ if (err)
+ return err;
+ if (!ptrace_may_access(task, mode)) {
+ mutex_unlock(&task->signal->cred_guard_mutex);
+ return -EPERM;
+ }
+ return 0;
+}
+
+static void task_access_unlock(struct task_struct *task)
+{
+ mutex_unlock(&task->signal->cred_guard_mutex);
+}

#ifdef CONFIG_KALLSYMS
/*
@@ -264,35 +281,18 @@ static int proc_pid_wchan(struct task_struct *task, char *buffer)
unsigned long wchan;
char symname[KSYM_NAME_LEN];

+ if (task_access_lock(task, PTRACE_MODE_READ))
+ return 0;
wchan = get_wchan(task);

+ task_access_unlock(task);
if (lookup_symbol_name(wchan, symname) < 0)
- if (!ptrace_may_access(task, PTRACE_MODE_READ))
- return 0;
- else
- return sprintf(buffer, "%lu", wchan);
+ return sprintf(buffer, "%lu", wchan);
else
return sprintf(buffer, "%s", symname);
}
#endif /* CONFIG_KALLSYMS */

-static int task_access_lock(struct task_struct *task, unsigned int mode)
-{
- int err = mutex_lock_killable(&task->signal->cred_guard_mutex);
- if (err)
- return err;
- if (!ptrace_may_access(task, mode)) {
- mutex_unlock(&task->signal->cred_guard_mutex);
- return -EPERM;
- }
- return 0;
-}
-
-static void task_access_unlock(struct task_struct *task)
-{
- mutex_unlock(&task->signal->cred_guard_mutex);
-}
-
#ifdef CONFIG_STACKTRACE

#define MAX_STACK_TRACE_DEPTH 64
@@ -512,23 +512,6 @@ static int proc_pid_syscall(struct task_struct *task, char *buffer)
/* Here the fs part begins */
/************************************************************************/

-/* permission checks */
-static int proc_fd_access_allowed(struct inode *inode)
-{
- struct task_struct *task;
- int allowed = 0;
- /* Allow access to a task's file descriptors if it is us or we
- * may use ptrace attach to the process and find out that
- * information.
- */
- task = get_proc_task(inode);
- if (task) {
- allowed = ptrace_may_access(task, PTRACE_MODE_READ);
- put_task_struct(task);
- }
- return allowed;
-}
-
int proc_setattr(struct dentry *dentry, struct iattr *attr)
{
int error;
@@ -1425,17 +1408,21 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path)
static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
{
struct inode *inode = dentry->d_inode;
+ struct task_struct *task = get_proc_task(inode);
int error = -EACCES;

/* We don't need a base pointer in the /proc filesystem */
path_put(&nd->path);

/* Are we allowed to snoop on the tasks file descriptors? */
- if (!proc_fd_access_allowed(inode))
+ error = task_access_lock(task, PTRACE_MODE_READ);
+ if (error)
goto out;

error = PROC_I(inode)->op.proc_get_link(dentry, &nd->path);
+ task_access_unlock(task);
out:
+ put_task_struct(task);
return ERR_PTR(error);
}

@@ -1467,19 +1454,24 @@ static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int b
{
int error = -EACCES;
struct inode *inode = dentry->d_inode;
+ struct task_struct *task = get_proc_task(inode);
struct path path;

/* Are we allowed to snoop on the tasks file descriptors? */
- if (!proc_fd_access_allowed(inode))
+ error = task_access_lock(task, PTRACE_MODE_READ);
+ if (error)
goto out;

error = PROC_I(inode)->op.proc_get_link(dentry, &path);
if (error)
- goto out;
+ goto out_unlock;

error = do_proc_readlink(&path, buffer, buflen);
path_put(&path);
+out_unlock:
+ task_access_unlock(task);
out:
+ put_task_struct(task);
return error;
}

--
1.7.7.6