diff options
| -rw-r--r-- | exec-do-not-leave-bprm-interp-on-stack.patch | 118 | ||||
| -rw-r--r-- | exec-use-eloop-for-max-recursion-depth.patch | 144 | ||||
| -rw-r--r-- | 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 000000000..5198824ed --- /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@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@chromium.org> +Cc: halfdog <me@halfdog.net> +Cc: P J P <ppandit@redhat.com> +Cc: Alexander Viro <viro@zeniv.linux.org.uk> +Cc: <stable@vger.kernel.org> +Signed-off-by: Andrew Morton <akpm@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 000000000..a3c48884f --- /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@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@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> +--- + 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 8d62e9365..525e44a0b 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@redhat.com> +- CVE-2012-4530: stack disclosure binfmt_script load_script (rhbz 868285 880147) + * Sun Nov 25 2012 Josh Boyer <jwboyer@redhat.com> - 3.7.0-0.rc6.git4.1 - Linux v3.7-rc6-209-g194d983 |