[kernel] CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147)
Josh Boyer
jwboyer at fedoraproject.org
Mon Nov 26 14:25:56 UTC 2012
commit fee5e57d00c55a1a7b3415b6875cb2a0dd00a906
Author: Josh Boyer <jwboyer at redhat.com>
Date: Mon Nov 26 09:03:26 2012 -0500
CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147)
exec-do-not-leave-bprm-interp-on-stack.patch | 118 +++++++++++++++++++++
exec-use-eloop-for-max-recursion-depth.patch | 144 ++++++++++++++++++++++++++
kernel.spec | 13 ++-
3 files changed, 274 insertions(+), 1 deletions(-)
---
diff --git a/exec-do-not-leave-bprm-interp-on-stack.patch b/exec-do-not-leave-bprm-interp-on-stack.patch
new file mode 100644
index 0000000..5198824
--- /dev/null
+++ b/exec-do-not-leave-bprm-interp-on-stack.patch
@@ -0,0 +1,118 @@
+From 6752ab4cb863fc63ed85f1ca78a42235c09fad83 Mon Sep 17 00:00:00 2001
+From: Kees Cook <keescook at chromium.org>
+Date: Mon, 26 Nov 2012 09:07:50 -0500
+Subject: [PATCH 1/2] exec: do not leave bprm->interp on stack
+
+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 at chromium.org>
+Cc: halfdog <me at halfdog.net>
+Cc: P J P <ppandit at redhat.com>
+Cc: Alexander Viro <viro at zeniv.linux.org.uk>
+Cc: <stable at vger.kernel.org>
+Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
+---
+ fs/binfmt_misc.c | 5 ++++-
+ fs/binfmt_script.c | 4 +++-
+ fs/exec.c | 15 +++++++++++++++
+ include/linux/binfmts.h | 1 +
+ 4 files changed, 23 insertions(+), 2 deletions(-)
+
+diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
+index 790b3cd..772428d 100644
+--- a/fs/binfmt_misc.c
++++ b/fs/binfmt_misc.c
+@@ -176,7 +176,10 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
+ goto _error;
+ bprm->argc ++;
+
+- bprm->interp = iname; /* for binfmt_script */
++ /* Update interp in case binfmt_script needs it. */
++ retval = bprm_change_interp(iname, bprm);
++ if (retval < 0)
++ goto _error;
+
+ interp_file = open_exec (iname);
+ retval = PTR_ERR (interp_file);
+diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
+index d3b8c1f..df49d48 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.
+diff --git a/fs/exec.c b/fs/exec.c
+index 0039055..c6e6de4 100644
+--- a/fs/exec.c
++++ b/fs/exec.c
+@@ -1175,9 +1175,24 @@ void free_bprm(struct linux_binprm *bprm)
+ mutex_unlock(¤t->signal->cred_guard_mutex);
+ abort_creds(bprm->cred);
+ }
++ /* If a binfmt changed the interp, free it. */
++ if (bprm->interp != bprm->filename)
++ kfree(bprm->interp);
+ kfree(bprm);
+ }
+
++int bprm_change_interp(char *interp, struct linux_binprm *bprm)
++{
++ /* If a binfmt changed the interp, free it first. */
++ if (bprm->interp != bprm->filename)
++ kfree(bprm->interp);
++ bprm->interp = kstrdup(interp, GFP_KERNEL);
++ if (!bprm->interp)
++ return -ENOMEM;
++ return 0;
++}
++EXPORT_SYMBOL(bprm_change_interp);
++
+ /*
+ * install the new credentials for this executable
+ */
+diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
+index cfcc6bf..de0628e 100644
+--- a/include/linux/binfmts.h
++++ b/include/linux/binfmts.h
+@@ -114,6 +114,7 @@ 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);
+--
+1.8.0
+
diff --git a/exec-use-eloop-for-max-recursion-depth.patch b/exec-use-eloop-for-max-recursion-depth.patch
new file mode 100644
index 0000000..a3c4888
--- /dev/null
+++ b/exec-use-eloop-for-max-recursion-depth.patch
@@ -0,0 +1,144 @@
+From ba1b23d05259e31d30a78017cdfbc010dcb08aa6 Mon Sep 17 00:00:00 2001
+From: Kees Cook <keescook at chromium.org>
+Date: Mon, 26 Nov 2012 09:02:11 -0500
+Subject: [PATCH 2/2] exec: use -ELOOP for max recursion depth
+
+To avoid an explosion of request_module calls on a chain of abusive
+scripts, fail maximum recursion with -ELOOP instead of -ENOEXEC. As soon
+as maximum recursion depth is hit, the error will fail all the way back
+up the chain, aborting immediately.
+
+This also has the side-effect of stopping the user's shell from attempting
+to reexecute the top-level file as a shell script. As seen in the
+dash source:
+
+ if (cmd != path_bshell && errno == ENOEXEC) {
+ *argv-- = cmd;
+ *argv = cmd = path_bshell;
+ goto repeat;
+ }
+
+The above logic was designed for running scripts automatically that lacked
+the "#!" header, not to re-try failed recursion. On a legitimate -ENOEXEC,
+things continue to behave as the shell expects.
+
+Additionally, when tracking recursion, the binfmt handlers should not be
+involved. The recursion being tracked is the depth of calls through
+search_binary_handler(), so that function should be exclusively responsible
+for tracking the depth.
+
+Signed-off-by: Kees Cook <keescook at chromium.org>
+Cc: halfdog <me at halfdog.net>
+Cc: P J P <ppandit at redhat.com>
+Cc: Alexander Viro <viro at zeniv.linux.org.uk>
+Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
+---
+ fs/binfmt_em86.c | 1 -
+ fs/binfmt_misc.c | 6 ------
+ fs/binfmt_script.c | 4 +---
+ fs/exec.c | 10 +++++-----
+ include/linux/binfmts.h | 2 --
+ 5 files changed, 6 insertions(+), 17 deletions(-)
+
+diff --git a/fs/binfmt_em86.c b/fs/binfmt_em86.c
+index 2790c7e..575796a 100644
+--- a/fs/binfmt_em86.c
++++ b/fs/binfmt_em86.c
+@@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm *bprm,struct pt_regs *regs)
+ return -ENOEXEC;
+ }
+
+- 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 772428d..f0f1a06 100644
+--- a/fs/binfmt_misc.c
++++ b/fs/binfmt_misc.c
+@@ -117,10 +117,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
+ if (!enabled)
+ goto _ret;
+
+- retval = -ENOEXEC;
+- if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
+- goto _ret;
+-
+ /* to keep locking time low, we copy the interpreter string */
+ read_lock(&entries_lock);
+ fmt = check_file(bprm);
+@@ -200,8 +196,6 @@ static int load_misc_binary(struct linux_binprm *bprm, struct pt_regs *regs)
+ if (retval < 0)
+ goto _error;
+
+- bprm->recursion_depth++;
+-
+ retval = search_binary_handler (bprm, regs);
+ if (retval < 0)
+ goto _error;
+diff --git a/fs/binfmt_script.c b/fs/binfmt_script.c
+index df49d48..8ae4be1 100644
+--- a/fs/binfmt_script.c
++++ b/fs/binfmt_script.c
+@@ -22,15 +22,13 @@ static int load_script(struct linux_binprm *bprm,struct pt_regs *regs)
+ char interp[BINPRM_BUF_SIZE];
+ int retval;
+
+- if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!') ||
+- (bprm->recursion_depth > BINPRM_MAX_RECURSION))
++ if ((bprm->buf[0] != '#') || (bprm->buf[1] != '!'))
+ return -ENOEXEC;
+ /*
+ * This section does the #! interpretation.
+ * Sorta complicated, but hopefully it will work. -TYT
+ */
+
+- bprm->recursion_depth++;
+ allow_write_access(bprm->file);
+ fput(bprm->file);
+ bprm->file = NULL;
+diff --git a/fs/exec.c b/fs/exec.c
+index c6e6de4..85c1f9e 100644
+--- a/fs/exec.c
++++ b/fs/exec.c
+@@ -1371,6 +1371,10 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
+ struct linux_binfmt *fmt;
+ pid_t old_pid, old_vpid;
+
++ /* This allows 4 levels of binfmt rewrites before failing hard. */
++ if (depth > 5)
++ return -ELOOP;
++
+ retval = security_bprm_check(bprm);
+ if (retval)
+ return retval;
+@@ -1395,12 +1399,8 @@ int search_binary_handler(struct linux_binprm *bprm,struct pt_regs *regs)
+ if (!try_module_get(fmt->module))
+ continue;
+ read_unlock(&binfmt_lock);
++ bprm->recursion_depth = depth + 1;
+ retval = fn(bprm, regs);
+- /*
+- * Restore the depth counter to its starting value
+- * in this call, so we don't have to rely on every
+- * load_binary function to restore it on return.
+- */
+ bprm->recursion_depth = depth;
+ if (retval >= 0) {
+ if (depth == 0) {
+diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
+index de0628e..54135f6 100644
+--- a/include/linux/binfmts.h
++++ b/include/linux/binfmts.h
+@@ -54,8 +54,6 @@ struct linux_binprm {
+ #define BINPRM_FLAGS_EXECFD_BIT 1
+ #define BINPRM_FLAGS_EXECFD (1 << BINPRM_FLAGS_EXECFD_BIT)
+
+-#define BINPRM_MAX_RECURSION 4
+-
+ /* Function parameter for binfmt->coredump */
+ struct coredump_params {
+ siginfo_t *siginfo;
+--
+1.8.0
+
diff --git a/kernel.spec b/kernel.spec
index 8d62e93..525e44a 100644
--- a/kernel.spec
+++ b/kernel.spec
@@ -62,7 +62,7 @@ Summary: The Linux kernel
# For non-released -rc kernels, this will be appended after the rcX and
# gitX tags, so a 3 here would become part of release "0.rcX.gitX.3"
#
-%global baserelease 1
+%global baserelease 2
%global fedora_build %{baserelease}
# base_sublevel is the kernel version we're starting with and patching
@@ -773,6 +773,10 @@ Patch22125: Bluetooth-Add-support-for-BCM20702A0.patch
#rhbz 859485
Patch21226: vt-Drop-K_OFF-for-VC_MUTE.patch
+#rhbz CVE-2012-4530 868285 880147
+Patch21228: exec-do-not-leave-bprm-interp-on-stack.patch
+Patch21229: exec-use-eloop-for-max-recursion-depth.patch
+
# END OF PATCH DEFINITIONS
%endif
@@ -1486,6 +1490,10 @@ ApplyPatch Bluetooth-Add-support-for-BCM20702A0.patch
#rhbz 859485
ApplyPatch vt-Drop-K_OFF-for-VC_MUTE.patch
+#rhbz CVE-2012-4530 868285 880147
+ApplyPatch exec-do-not-leave-bprm-interp-on-stack.patch
+ApplyPatch exec-use-eloop-for-max-recursion-depth.patch
+
# END OF PATCH APPLICATIONS
%endif
@@ -2353,6 +2361,9 @@ fi
# ||----w |
# || ||
%changelog
+* Mon Nov 26 2012 Josh Boyer <jwboyer at redhat.com>
+- CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147)
+
* Sun Nov 25 2012 Josh Boyer <jwboyer at redhat.com> - 3.7.0-0.rc6.git4.1
- Linux v3.7-rc6-209-g194d983
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