From 21838dbf96ce1e94d1ba80fdd491f9a0a6352ff1 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 20 Dec 2012 15:05:16 -0800 Subject: exec: do not leave bprm->interp on stack commit b66c5984017533316fd1951770302649baf1aa33 upstream. If a series of scripts are executed, each triggering module loading via unprintable bytes in the script header, kernel stack contents can leak into the command line. Normally execution of binfmt_script and binfmt_misc happens recursively. However, when modules are enabled, and unprintable bytes exist in the bprm->buf, execution will restart after attempting to load matching binfmt modules. Unfortunately, the logic in binfmt_script and binfmt_misc does not expect to get restarted. They leave bprm->interp pointing to their local stack. This means on restart bprm->interp is left pointing into unused stack memory which can then be copied into the userspace argv areas. After additional study, it seems that both recursion and restart remains the desirable way to handle exec with scripts, misc, and modules. As such, we need to protect the changes to interp. This changes the logic to require allocation for any changes to the bprm->interp. To avoid adding a new kmalloc to every exec, the default value is left as-is. Only when passing through binfmt_script or binfmt_misc does an allocation take place. For a proof of concept, see DoTest.sh from: http://www.halfdog.net/Security/2012/LinuxKernelBinfmtScriptStackDataDisclosure/ Signed-off-by: Kees Cook Cc: halfdog Cc: P J P Cc: Alexander Viro Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- fs/binfmt_script.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) (limited to 'fs/binfmt_script.c') diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c index d3b8c1f6315..df49d486b0c 100644 --- a/fs/binfmt_script.c +++ b/fs/binfmt_script.c @@ -82,7 +82,9 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs) retval = copy_strings_kernel(1, &i_name, bprm); if (retval) return retval; bprm->argc++; - bprm->interp = interp; + retval = bprm_change_interp(interp, bprm); + if (retval < 0) + return retval; /* * OK, now restart the process with the interpreter's dentry. -- cgit v1.2.3-18-g5258