[kernel] r19595 - in dists/sid/linux/debian: . patches patches/bugfix/all
Ben Hutchings
benh at alioth.debian.org
Sun Dec 9 20:17:53 UTC 2012
Author: benh
Date: Sun Dec 9 20:17:53 2012
New Revision: 19595
Log:
exec: Two bug fixes in binfmt recursion
Added:
dists/sid/linux/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch
dists/sid/linux/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch
Modified:
dists/sid/linux/debian/changelog
dists/sid/linux/debian/patches/series
Modified: dists/sid/linux/debian/changelog
==============================================================================
--- dists/sid/linux/debian/changelog Sun Dec 9 20:13:50 2012 (r19594)
+++ dists/sid/linux/debian/changelog Sun Dec 9 20:17:53 2012 (r19595)
@@ -97,6 +97,8 @@
* [x86] KVM: x86: invalid opcode oops on SET_SREGS with OSXSAVE bit set
(CVE-2012-4461)
* kmod: make __request_module() killable (CVE-2012-4398)
+ * exec: do not leave bprm->interp on stack (CVE-2012-4530)
+ * exec: use -ELOOP for max recursion depth
[ Ian Campbell ]
* [xen] add support for microcode updating. (Closes: #693053)
Added: dists/sid/linux/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ dists/sid/linux/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch Sun Dec 9 20:17:53 2012 (r19595)
@@ -0,0 +1,115 @@
+From: Kees Cook <keescook at chromium.org>
+Date: Thu, 6 Dec 2012 17:00:21 +1100
+Subject: [1/2] exec: do not leave bprm->interp on stack
+
+commit 1e1b8374592f5fb347625e84d8a5f2f40d858a24 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 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_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 b0b70fb..b0c1755 100644
+--- a/fs/binfmt_misc.c
++++ b/fs/binfmt_misc.c
+@@ -176,7 +176,10 @@ static int load_misc_binary(struct linux_binprm *bprm)
+ 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 8c95499..4834f2c 100644
+--- a/fs/binfmt_script.c
++++ b/fs/binfmt_script.c
+@@ -82,7 +82,9 @@ static int load_script(struct linux_binprm *bprm)
+ 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 b71b08c..bf50973 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 2630c9b..7f0e297 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);
Added: dists/sid/linux/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch
==============================================================================
--- /dev/null 00:00:00 1970 (empty, because file is newly added)
+++ dists/sid/linux/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch Sun Dec 9 20:17:53 2012 (r19595)
@@ -0,0 +1,133 @@
+From: Kees Cook <keescook at chromium.org>
+Date: Thu, 6 Dec 2012 17:00:21 +1100
+Subject: [2/2] exec: use -ELOOP for max recursion depth
+
+commit a4706fd3dc5d23f58da814d03f3ef92fd9a4fc16 upstream.
+
+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>
+[bwh: Backported to 3.2: adjust context]
+---
+ 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(-)
+
+--- a/fs/binfmt_em86.c
++++ b/fs/binfmt_em86.c
+@@ -42,7 +42,6 @@ static int load_em86(struct linux_binprm
+ return -ENOEXEC;
+ }
+
+- bprm->recursion_depth++; /* Well, the bang-shell is implicit... */
+ allow_write_access(bprm->file);
+ fput(bprm->file);
+ bprm->file = NULL;
+--- a/fs/binfmt_misc.c
++++ b/fs/binfmt_misc.c
+@@ -116,10 +116,6 @@ static int load_misc_binary(struct linux
+ 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);
+@@ -199,8 +195,6 @@ static int load_misc_binary(struct linux
+ if (retval < 0)
+ goto _error;
+
+- bprm->recursion_depth++;
+-
+ retval = search_binary_handler (bprm, regs);
+ if (retval < 0)
+ goto _error;
+--- a/fs/binfmt_script.c
++++ b/fs/binfmt_script.c
+@@ -22,15 +22,13 @@ static int load_script(struct linux_binp
+ 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;
+--- a/fs/exec.c
++++ b/fs/exec.c
+@@ -1384,6 +1384,10 @@ int search_binary_handler(struct linux_b
+ struct linux_binfmt *fmt;
+ pid_t old_pid;
+
++ /* This allows 4 levels of binfmt rewrites before failing hard. */
++ if (depth > 5)
++ return -ELOOP;
++
+ retval = security_bprm_check(bprm);
+ if (retval)
+ return retval;
+@@ -1407,12 +1411,8 @@ int search_binary_handler(struct linux_b
+ 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)
+--- a/include/linux/binfmts.h
++++ b/include/linux/binfmts.h
+@@ -67,8 +67,6 @@ 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 {
+ long signr;
Modified: dists/sid/linux/debian/patches/series
==============================================================================
--- dists/sid/linux/debian/patches/series Sun Dec 9 20:13:50 2012 (r19594)
+++ dists/sid/linux/debian/patches/series Sun Dec 9 20:17:53 2012 (r19595)
@@ -428,3 +428,5 @@
bugfix/all/usermodehelper-____call_usermodehelper-doesnt-need-do_exit.patch
bugfix/all/kmod-introduce-call_modprobe-helper.patch
bugfix/all/kmod-make-__request_module-killable.patch
+bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch
+bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch
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