Re: 4096 byte limit to /proc/PID/environ ?

James Pearson
2006-06-01T14:11:29Z

H. Peter Anvin wrote:
> I think this is the wrong approach.
>
> Many of these should probably be converted to seq_file, but in the
> particular case of environ, the right approach is to observe the fact
> that reading environ is just like reading /proc/PID/mem, except:
>
> a. the access restrictions are less strict, and
> b. there is a range restriction, which needs to be enforced, and
> c. there is an offset.
>
> Pretty much, take the guts from /proc/PID/mem and generalize it
> slightly, and you have the code that can run either /proc/PID/mem or
> /proc/PID/environ.

The following patch is based on the /proc/PID/mem code appears to work fine.

James Pearson

--- ./fs/proc/base.c.dist 2006-05-11 02:56:24.000000000 +0100
+++ ./fs/proc/base.c 2006-06-01 13:40:50.865851007 +0100
@@ -409,22 +409,6 @@
(task->state == TASK_STOPPED || task->state == TASK_TRACED) && \
security_ptrace(current,task) == 0))

-static int proc_pid_environ(struct task_struct *task, char * buffer)
-{
- int res = 0;
- struct mm_struct *mm = get_task_mm(task);
- if (mm) {
- unsigned int len = mm->env_end - mm->env_start;
- if (len > PAGE_SIZE)
- len = PAGE_SIZE;
- res = access_process_vm(task, mm->env_start, buffer,
len, 0);
- if (!ptrace_may_attach(task))
- res = -ESRCH;
- mmput(mm);
- }
- return res;
-}
-
static int proc_pid_cmdline(struct task_struct *task, char * buffer)
{
int res = 0;
@@ -897,6 +881,80 @@
.open = mem_open,
};

+static ssize_t env_read(struct file * file, char __user * buf,
+ size_t count, loff_t *ppos)
+{
+ struct task_struct *task = proc_task(file->f_dentry->d_inode);
+ char *page;
+ unsigned long src = *ppos;
+ int ret = -ESRCH;
+ struct mm_struct *mm;
+ size_t max_len;
+
+ if (!ptrace_may_attach(task))
+ goto out;
+
+ ret = -ENOMEM;
+ page = (char *)__get_free_page(GFP_USER);
+ if (!page)
+ goto out;
+
+ ret = 0;
+
+ mm = get_task_mm(task);
+ if (!mm)
+ goto out_free;
+
+ ret = 0;
+ max_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
+
+ while (count > 0) {
+ int this_len, retval;
+
+ this_len = mm->env_end - (mm->env_start + src);
+
+ if (this_len <= 0) {
+ break;
+ }
+
+ if (this_len > max_len)
+ this_len = max_len;
+
+ retval = access_process_vm(task, (mm->env_start + src),
page, this_len, 0);
+
+ if (!ptrace_may_attach(task)) {
+ ret = -ESRCH;
+ break;
+ }
+
+ if (retval <= 0) {
+ ret = retval;
+ break;
+ }
+
+ if (copy_to_user(buf, page, retval)) {
+ ret = -EFAULT;
+ break;
+ }
+
+ ret += retval;
+ src += retval;
+ buf += retval;
+ count -= retval;
+ }
+ *ppos = src;
+
+ mmput(mm);
+out_free:
+ free_page((unsigned long) page);
+out:
+ return ret;
+}
+
+static struct file_operations proc_env_operations = {
+ .read = env_read,
+};
+
static ssize_t oom_adjust_read(struct file *file, char __user *buf,
size_t count, loff_t *ppos)
{
@@ -1675,11 +1733,6 @@
inode->i_op = &proc_pid_link_inode_operations;
ei->op.proc_get_link = proc_root_link;
break;
- case PROC_TID_ENVIRON:
- case PROC_TGID_ENVIRON:
- inode->i_fop = &proc_info_file_operations;
- ei->op.proc_read = proc_pid_environ;
- break;
case PROC_TID_AUXV:
case PROC_TGID_AUXV:
inode->i_fop = &proc_info_file_operations;
@@ -1723,6 +1776,10 @@
inode->i_op = &proc_mem_inode_operations;
inode->i_fop = &proc_mem_operations;
break;
+ case PROC_TID_ENVIRON:
+ case PROC_TGID_ENVIRON:
+ inode->i_fop = &proc_env_operations;
+ break;
#ifdef CONFIG_SECCOMP