Allow recursion in binfmt_script and binfmt_misc

binfmt_script and binfmt_misc disallow recursion to avoid stack overflow
using sh_bang and misc_bang.  It causes problem in some cases:

$ echo '#!/bin/ls' > /tmp/t0
$ echo '#!/tmp/t0' > /tmp/t1
$ echo '#!/tmp/t1' > /tmp/t2
$ chmod +x /tmp/t*
$ /tmp/t2
zsh: exec format error: /tmp/t2

Similar problem with binfmt_misc.

This patch introduces field 'recursion_depth' into struct linux_binprm to
track recursion level in binfmt_misc and binfmt_script.  If recursion
level more then BINPRM_MAX_RECURSION it generates -ENOEXEC.

[akpm@linux-foundation.org: make linux_binprm.recursion_depth a uint]
Signed-off-by: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 54980a3c7602..7394b5b349ff 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -39,6 +39,7 @@ struct linux_binprm{
 #ifdef __alpha__
         unsigned int taso:1;
 #endif
+        unsigned int recursion_depth;
         struct file * file;
         int e_uid, e_gid;
         kernel_cap_t cap_post_exec_permitted;
@@ -61,6 +62,7 @@ struct linux_binprm{
 #define BINPRM_FLAGS_EXECFD_BIT 1
 #define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT)
 
+#define BINPRM_MAX_RECURSION 4
 
 /*
  * This structure defines the functions that are used to load the binary formats that