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>
diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c
index f9c88d0..32fb00b 100644
--- a/fs/binfmt_em86.c
+++ b/fs/binfmt_em86.c
@@ -43,7 +43,7 @@
return -ENOEXEC;
}
- bprm->sh_bang = 1; /* Well, the bang-shell is implicit... */
+ bprm->recursion_depth++; /* Well, the bang-shell is implicit... */
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 8d7e88e..f2744ab 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -117,7 +117,7 @@
goto _ret;
retval = -ENOEXEC;
- if (bprm->misc_bang)
+ if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
goto _ret;
/* to keep locking time low, we copy the interpreter string */
@@ -197,7 +197,7 @@
if (retval < 0)
goto _error;
- bprm->misc_bang = 1;
+ bprm->recursion_depth++;
retval = search_binary_handler (bprm, regs);
if (retval < 0)
diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
index 9e3963f..0834350 100644
--- a/fs/binfmt_script.c
+++ b/fs/binfmt_script.c
@@ -22,14 +22,15 @@
char interp[BINPRM_BUF_SIZE];
int retval;
- if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') || (bprm->sh_bang))
+ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') ||
+ (bprm->recursion_depth > BINPRM_MAX_RECURSION))
return -ENOEXEC;
/*
* This section does the #! interpretation.
* Sorta complicated, but hopefully it will work. -TYT
*/
- bprm->sh_bang = 1;
+ bprm->recursion_depth++;
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 54980a3..7394b5b 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -39,6 +39,7 @@
#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 @@
#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
