3:48 a.m.
From: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
The purpose of audit_bprm() is to log the argv array to a userspace daemon at
the end of the execve system call. Since user-space hasn't had time to run,
this array is still in pristine state on the process' stack; so no need to
copy it, we can just grab it from there.
In order to minimize the damage to audit_log_*() copy each string into a
temporary kernel buffer first.
Currently the audit code requires that the full argument vector fits in a
single packet. So currently it does clip the argv size to a (sysctl) limit,
but only when execve auditing is enabled.
If the audit protocol gets extended to allow for multiple packets this check
can be removed.
Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl>
Signed-off-by: Ollie Wild <aaw(a)google.com>
Cc: <linux-audit(a)redhat.com>
Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org>
---
Documentation/filesystems/proc.txt | 7 ++
fs/exec.c | 3
include/linux/binfmts.h | 1
kernel/auditsc.c | 84 ++++++++++++++++++++-------
kernel/sysctl.c | 11 +++
5 files changed, 85 insertions(+), 21 deletions(-)
diff -puN Documentation/filesystems/proc.txt~audit-rework-execve-audit
Documentation/filesystems/proc.txt
--- a/Documentation/filesystems/proc.txt~audit-rework-execve-audit
+++ a/Documentation/filesystems/proc.txt
@@ -1065,6 +1065,13 @@ check the amount of free space (value is
resume it if we have a value of 3 or more percent; consider information about
the amount of free space valid for 30 seconds
+audit_argv_kb
+-------------
+
+The file contains a single value denoting the limit on the argv array size
+for execve (in KiB). This limit is only applied when system call auditing for
+execve is enabled, otherwise the value is ignored.
+
ctrl-alt-del
------------
diff -puN fs/exec.c~audit-rework-execve-audit fs/exec.c
--- a/fs/exec.c~audit-rework-execve-audit
+++ a/fs/exec.c
@@ -1154,6 +1154,7 @@ int do_execve(char * filename,
{
struct linux_binprm *bprm;
struct file *file;
+ unsigned long env_p;
int retval;
int i;
@@ -1208,9 +1209,11 @@ int do_execve(char * filename,
if (retval < 0)
goto out;
+ env_p = bprm->p;
retval = copy_strings(bprm->argc, argv, bprm);
if (retval < 0)
goto out;
+ bprm->argv_len = env_p - bprm->p;
retval = search_binary_handler(bprm,regs);
if (retval >= 0) {
diff -puN include/linux/binfmts.h~audit-rework-execve-audit include/linux/binfmts.h
--- a/include/linux/binfmts.h~audit-rework-execve-audit
+++ a/include/linux/binfmts.h
@@ -40,6 +40,7 @@ struct linux_binprm{
unsigned interp_flags;
unsigned interp_data;
unsigned long loader, exec;
+ unsigned long argv_len;
};
#define BINPRM_FLAGS_ENFORCE_NONDUMP_BIT 0
diff -puN kernel/auditsc.c~audit-rework-execve-audit kernel/auditsc.c
--- a/kernel/auditsc.c~audit-rework-execve-audit
+++ a/kernel/auditsc.c
@@ -153,7 +153,7 @@ struct audit_aux_data_execve {
struct audit_aux_data d;
int argc;
int envc;
- char mem[0];
+ struct mm_struct *mm;
};
struct audit_aux_data_socketcall {
@@ -831,6 +831,55 @@ static int audit_log_pid_context(struct
return rc;
}
+static void audit_log_execve_info(struct audit_buffer *ab,
+ struct audit_aux_data_execve *axi)
+{
+ int i;
+ long len, ret;
+ const char __user *p = (const char __user *)axi->mm->arg_start;
+ char *buf;
+
+ if (axi->mm != current->mm)
+ return; /* execve failed, no additional info */
+
+ for (i = 0; i < axi->argc; i++, p += len) {
+ len = strnlen_user(p, MAX_ARG_PAGES*PAGE_SIZE);
+ /*
+ * We just created this mm, if we can't find the strings
+ * we just copied into it something is _very_ wrong. Similar
+ * for strings that are too long, we should not have created
+ * any.
+ */
+ if (!len || len > MAX_ARG_STRLEN) {
+ WARN_ON(1);
+ send_sig(SIGKILL, current, 0);
+ }
+
+ buf = kmalloc(len, GFP_KERNEL);
+ if (!buf) {
+ audit_panic("out of memory for argv string\n");
+ break;
+ }
+
+ ret = copy_from_user(buf, p, len);
+ /*
+ * There is no reason for this copy to be short. We just
+ * copied them here, and the mm hasn't been exposed to user-
+ * space yet.
+ */
+ if (!ret) {
+ WARN_ON(1);
+ send_sig(SIGKILL, current, 0);
+ }
+
+ audit_log_format(ab, "a%d=", i);
+ audit_log_untrustedstring(ab, buf);
+ audit_log_format(ab, "\n");
+
+ kfree(buf);
+ }
+}
+
static void audit_log_exit(struct audit_context *context, struct task_struct *tsk)
{
int i, call_panic = 0;
@@ -971,13 +1020,7 @@ static void audit_log_exit(struct audit_
case AUDIT_EXECVE: {
struct audit_aux_data_execve *axi = (void *)aux;
- int i;
- const char *p;
- for (i = 0, p = axi->mem; i < axi->argc; i++) {
- audit_log_format(ab, "a%d=", i);
- p = audit_log_untrustedstring(ab, p);
- audit_log_format(ab, "\n");
- }
+ audit_log_execve_info(ab, axi);
break; }
case AUDIT_SOCKETCALL: {
@@ -1821,32 +1864,31 @@ int __audit_ipc_set_perm(unsigned long q
return 0;
}
+int audit_argv_kb = 32;
+
int audit_bprm(struct linux_binprm *bprm)
{
struct audit_aux_data_execve *ax;
struct audit_context *context = current->audit_context;
- unsigned long p, next;
- void *to;
if (likely(!audit_enabled || !context || context->dummy))
return 0;
- ax = kmalloc(sizeof(*ax) + PAGE_SIZE * MAX_ARG_PAGES - bprm->p,
- GFP_KERNEL);
+ /*
+ * Even though the stack code doesn't limit the arg+env size any more,
+ * the audit code requires that _all_ arguments be logged in a single
+ * netlink skb. Hence cap it :-(
+ */
+ if (bprm->argv_len > (audit_argv_kb << 10))
+ return -E2BIG;
+
+ ax = kmalloc(sizeof(*ax), GFP_KERNEL);
if (!ax)
return -ENOMEM;
ax->argc = bprm->argc;
ax->envc = bprm->envc;
- for (p = bprm->p, to = ax->mem; p < MAX_ARG_PAGES*PAGE_SIZE; p = next) {
- struct page *page = bprm->page[p / PAGE_SIZE];
- void *kaddr = kmap(page);
- next = (p + PAGE_SIZE) & ~(PAGE_SIZE - 1);
- memcpy(to, kaddr + (p & (PAGE_SIZE - 1)), next - p);
- to += next - p;
- kunmap(page);
- }
-
+ ax->mm = bprm->mm;
ax->d.type = AUDIT_EXECVE;
ax->d.next = context->aux;
context->aux = (void *)ax;
diff -puN kernel/sysctl.c~audit-rework-execve-audit kernel/sysctl.c
--- a/kernel/sysctl.c~audit-rework-execve-audit
+++ a/kernel/sysctl.c
@@ -78,6 +78,7 @@ extern int percpu_pagelist_fraction;
extern int compat_log;
extern int maps_protect;
extern int sysctl_stat_interval;
+extern int audit_argv_kb;
/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
@@ -306,6 +307,16 @@ static ctl_table kern_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+#ifdef CONFIG_AUDITSYSCALL
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "audit_argv_kb",
+ .data = &audit_argv_kb,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+#endif
{
.ctl_name = KERN_CORE_PATTERN,
.procname = "core_pattern",
_