diff --git a/debian/changelog b/debian/changelog index 6303ba9af..f5bb73633 100644 --- a/debian/changelog +++ b/debian/changelog @@ -97,6 +97,8 @@ linux (3.2.35-1) UNRELEASED; urgency=low * [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) diff --git a/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch b/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch new file mode 100644 index 000000000..45a4ac26b --- /dev/null +++ b/debian/patches/bugfix/all/exec-do-not-leave-bprm-interp-on-stack.patch @@ -0,0 +1,115 @@ +From: Kees Cook +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 +Cc: halfdog +Cc: P J P +Cc: Alexander Viro +Signed-off-by: Andrew Morton +--- + 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); diff --git a/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch b/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch new file mode 100644 index 000000000..633314f80 --- /dev/null +++ b/debian/patches/bugfix/all/exec-use-ELOOP-for-max-recursion-depth.patch @@ -0,0 +1,133 @@ +From: Kees Cook +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 +Cc: halfdog +Cc: P J P +Cc: Alexander Viro +Signed-off-by: Andrew Morton +[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; diff --git a/debian/patches/series b/debian/patches/series index 1f2792ccd..bf13511dd 100644 --- a/debian/patches/series +++ b/debian/patches/series @@ -428,3 +428,5 @@ bugfix/all/usermodehelper-implement-UMH_KILLABLE.patch 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