diff options
| author | Kees Cook <keescook@chromium.org> | 2012-12-20 15:05:16 -0800 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2013-01-03 03:33:45 +0000 |
| commit | 5f124a5db0b3f59232e24586ee75928793c87efb (patch) | |
| tree | a4363688a0ad0dbdf4979673ee7e2d1e3700b7ac /include | |
| parent | 150086ca6bd7493e7753f923a3f55e73701253b3 (diff) | |
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 <keescook@chromium.org>
Cc: halfdog <me@halfdog.net>
Cc: P J P <ppandit@redhat.com>
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>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/binfmts.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index fd88a3945aa1..f606406d5fd6 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -127,6 +127,7 @@ extern int setup_arg_pages(struct linux_binprm * bprm, unsigned long stack_top, int executable_stack); extern int bprm_mm_init(struct linux_binprm *bprm); +extern int bprm_change_interp(char *interp, struct linux_binprm *bprm); extern int copy_strings_kernel(int argc, const char *const *argv, struct linux_binprm *bprm); extern int prepare_bprm_creds(struct linux_binprm *bprm); |