This change allows us to take advantage of access_remote_vm(), which in turn
eliminates a security issue with the mem_write() implementation.
The previous implementation of mem_write() was insecure since the target task
could exec a setuid-root binary between the permission check and the actual
write. Holding a reference to the target mm_struct eliminates this
vulnerability.
Signed-off-by: Stephen Wilson <wilsons@xxxxxxxx>
---
fs/proc/base.c | 58 ++++++++++++++++++++++++++++++++-----------------------
1 files changed, 34 insertions(+), 24 deletions(-)
diff --git a/fs/proc/base.c b/fs/proc/base.c
index f6b644f..2af83bd 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -191,14 +191,20 @@ static int proc_root_link(struct inode *inode, struct path *path)
return result;
}
-static int __check_mem_permission(struct task_struct *task)
+static struct mm_struct *__check_mem_permission(struct task_struct *task)
{
+ struct mm_struct *mm;
+
+ mm = get_task_mm(task);
+ if (!mm)
+ return ERR_PTR(-EINVAL);
+
/*
* A task can always look at itself, in case it chooses
* to use system calls instead of load instructions.
*/
if (task == current)
- return 0;
+ return mm;
/*
* If current is actively ptrace'ing, and would also be
@@ -210,20 +216,23 @@ static int __check_mem_permission(struct task_struct *task)
match = (tracehook_tracer_task(task) == current);
rcu_read_unlock();
if (match && ptrace_may_access(task, PTRACE_MODE_ATTACH))
- return 0;
+ return mm;
}
/*
* Noone else is allowed.
*/
- return -EPERM;
+ mmput(mm);
+ return ERR_PTR(-EPERM);
}
/*
- * Return zero if current may access user memory in @task, -error if not.
+ * If current may access user memory in @task return a reference to the
+ * corresponding mm, otherwise ERR_PTR.
*/
-static int check_mem_permission(struct task_struct *task)
+static struct mm_struct *check_mem_permission(struct task_struct *task)
{
+ struct mm_struct *mm;
int err;
/*
@@ -232,12 +241,12 @@ static int check_mem_permission(struct task_struct *task)
*/
err = mutex_lock_killable(&task->signal->cred_guard_mutex);
if (err)
- return err;
+ return ERR_PTR(err);
- err = __check_mem_permission(task);
+ mm = __check_mem_permission(task);
mutex_unlock(&task->signal->cred_guard_mutex);
- return err;
+ return mm;
}
struct mm_struct *mm_for_maps(struct task_struct *task)
@@ -793,18 +802,14 @@ static ssize_t mem_read(struct file * file, char __user * buf,
if (!task)
goto out_no_task;
- if (check_mem_permission(task))
- goto out;
-
ret = -ENOMEM;
page = (char *)__get_free_page(GFP_TEMPORARY);
if (!page)
goto out;
- ret = 0;
-
- mm = get_task_mm(task);
- if (!mm)
+ mm = check_mem_permission(task);
+ ret = PTR_ERR(mm);
+ if (IS_ERR(mm))
goto out_free;
ret = -EIO;
@@ -818,8 +823,8 @@ static ssize_t mem_read(struct file * file, char __user * buf,
int this_len, retval;
this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
- retval = access_process_vm(task, src, page, this_len, 0);
- if (!retval || check_mem_permission(task)) {
+ retval = access_remote_vm(mm, src, page, this_len, 0);
+ if (!retval) {
if (!ret)
ret = -EIO;
break;
@@ -858,22 +863,25 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
char *page;
struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
unsigned long dst = *ppos;
+ struct mm_struct *mm;
copied = -ESRCH;
if (!task)
goto out_no_task;
- if (check_mem_permission(task))
- goto out;
+ mm = check_mem_permission(task);
+ copied = PTR_ERR(mm);
+ if (IS_ERR(mm))
+ goto out_task;
copied = -EIO;
if (file->private_data != (void *)((long)current->self_exec_id))
- goto out;
+ goto out_mm;
copied = -ENOMEM;
page = (char *)__get_free_page(GFP_TEMPORARY);
if (!page)
- goto out;
+ goto out_mm;
copied = 0;
while (count > 0) {
@@ -884,7 +892,7 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
copied = -EFAULT;
break;
}
- retval = access_process_vm(task, dst, page, this_len, 1);
+ retval = access_remote_vm(mm, dst, page, this_len, 1);
if (!retval) {
if (!copied)
copied = -EIO;
@@ -897,7 +905,9 @@ static ssize_t mem_write(struct file * file, const char __user *buf,
}
*ppos = dst;
free_page((unsigned long) page);
-out:
+out_mm:
+ mmput(mm);
+out_task:
put_task_struct(task);
out_no_task:
return copied;
--
1.7.3.5
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