busybox/examples/linux-2.6.30_proc_self_exe.patch

This patch makes /proc/self/exe executable even if proc
is not mounted. It is especially useful on NOMMU arches.

diff -urp ../linux-2.6.30.org/fs/exec.c linux-2.6.30/fs/exec.c
--- ../linux-2.6.30.org/fs/exec.c	2009-06-10 05:05:27.000000000 +0200
+++ linux-2.6.30/fs/exec.c	2009-06-25 00:20:13.000000000 +0200
@@ -652,9 +652,25 @@ struct file *open_exec(const char *name)
 	file = do_filp_open(AT_FDCWD, name,
 				O_LARGEFILE | O_RDONLY | FMODE_EXEC, 0,
 				MAY_EXEC | MAY_OPEN);
-	if (IS_ERR(file))
-		goto out;
+	if (IS_ERR(file)) {
+		if ((PTR_ERR(file) == -ENOENT || PTR_ERR(file) == -EACCES)
+		 && strcmp(name, "/proc/self/exe") == 0
+		) {
+			struct file *sv = file;
+			struct mm_struct *mm;
 
+			mm = get_task_mm(current);
+			if (!mm)
+				goto out;
+			file = get_mm_exe_file(mm);
+			mmput(mm);
+			if (file)
+				goto ok;
+			file = sv;
+		}
+		goto out;
+	}
+ok:
 	err = -EACCES;
 	if (!S_ISREG(file->f_path.dentry->d_inode->i_mode))
 		goto exit;