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

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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
                case PROC_TID_SECCOMP:
                case PROC_TGID_SECCOMP:
-
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