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Message-ID: <50D23223.6020505@gmail.com>
Date: Thu, 20 Dec 2012 08:31:15 +1100
From: Michael Cassaniti <m.cassaniti@...il.com>
To: Linux Security Module mailing list
<linux-security-module@...r.kernel.org>,
linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] security: seccomp as extended attribute
From Michael Cassaniti <m.cassaniti@...il.com>
Add seccomp filter via extended attribute
Written against Linux 3.5
Signed-off-by: Michael Cassaniti <m.cassaniti@...il.com>
---
diff -uprN -X linux-3.5-rp1/Documentation/dontdiff
linux-3.5-rp1/include/linux/seccomp.h linux-3.5-rp2/include/linux/seccomp.h
--- linux-3.5-rp1/include/linux/seccomp.h 2012-09-21
12:43:28.215772113 +1000
+++ linux-3.5-rp2/include/linux/seccomp.h 2012-09-21
12:44:09.915410558 +1000
@@ -127,6 +127,11 @@ extern u32 seccomp_bpf_load(int off);
#define SECCOMP_XATTR_BIT_DEF_RETURN 2
#define SECCOMP_XATTR_BITMAP_START 3
+#define SECCOMP_FILTER_LOAD_SYSCALL BPF_STMT(BPF_LD|BPF_W|BPF_ABS,
BPF_DATA(nr))
+#define SECCOMP_FILTER_ALLOW BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW)
+#define SECCOMP_FILTER_KILL BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_KILL)
+#define SECCOMP_FILTER_DENY BPF_STMT(BPF_RET|BPF_K,
(SECCOMP_RET_ERRNO|EPERM))
+
#else /* CONFIG_SECCOMP_FILTER */
static inline void put_seccomp_filter(struct task_struct *tsk)
{
diff -uprN -X linux-3.5-rp1/Documentation/dontdiff
linux-3.5-rp1/kernel/seccomp.c linux-3.5-rp2/kernel/seccomp.c
--- linux-3.5-rp1/kernel/seccomp.c 2012-09-21 13:23:52.254969072 +1000
+++ linux-3.5-rp2/kernel/seccomp.c 2012-09-21 14:43:27.687445601 +1000
@@ -18,6 +18,9 @@
#include <linux/compat.h>
#include <linux/sched.h>
#include <linux/seccomp.h>
+#include <linux/dcache.h> /* for dget() and struct dentry */
+#include <linux/binfmts.h> /* for struct binprm */
+#include <linux/fs.h> /* for struct inode */
/* #define SECCOMP_DEBUG 1 */
@@ -224,7 +227,7 @@ static u32 seccomp_run_filters(int sysca
*
* Returns 0 on success or an errno on failure.
*/
-static long seccomp_attach_filter(struct sock_fprog *fprog)
+static long seccomp_attach_filter(struct sock_fprog *fprog, int copy_mode)
{
struct seccomp_filter *filter;
unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
@@ -252,16 +255,22 @@ static long seccomp_attach_filter(struct
/* Allocate a new seccomp_filter */
filter = kzalloc(sizeof(struct seccomp_filter) + fp_size,
- GFP_KERNEL|__GFP_NOWARN);
+ GFP_KERNEL|__GFP_NOWARN);
if (!filter)
return -ENOMEM;
+
atomic_set(&filter->usage, 1);
filter->len = fprog->len;
/* Copy the instructions from fprog. */
ret = -EFAULT;
- if (copy_from_user(filter->insns, fprog->filter, fp_size))
- goto fail;
+ if (copy_mode) {
+ if (memcpy(filter->insns, fprog->filter, fp_size))
+ goto fail;
+ } else {
+ if (copy_from_user(filter->insns, fprog->filter, fp_size))
+ goto fail;
+ }
/* Check and rewrite the fprog via the skb checker */
ret = sk_chk_filter(filter->insns, filter->len);
@@ -307,7 +316,7 @@ long seccomp_attach_user_filter(char __u
#endif
if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
goto out;
- ret = seccomp_attach_filter(&fprog);
+ ret = seccomp_attach_filter(&fprog, 0);
out:
return ret;
}
@@ -503,8 +512,168 @@ out:
return ret;
}
-int append_seccomp_from_vfs(struct linux_binprm *bprm)
+int get_seccomp_xattr_from_vfs(struct linux_binprm *bprm,
+ unsigned char *bitmap)
{
- pr_debug("Entered stub %s\n", __func__);
+ int size;
+ struct dentry *dentry;
+ struct inode *inode;
+
+ dentry = dget(bprm->file->f_dentry);
+ if (!dentry)
+ return -EINVAL;
+
+ inode = dentry->d_inode;
+ if (!inode || !inode->i_op->getxattr)
+ return -EOPNOTSUPP;
+
+ size = inode->i_op->getxattr((struct dentry *)dentry,
+ SECCOMP_XATTR_NAME, bitmap,
+ SECCOMP_XATTR_LEN);
+
+ if (size == -ENODATA || size == -EOPNOTSUPP)
+ return -EOPNOTSUPP;
+
+ if (size != SECCOMP_XATTR_LEN) {
+ pr_notice("%s: Got invalid seccomp xattr for %s\n",
+ __func__, bprm->filename);
+ return -EINVAL;
+ }
+
return 0;
}
+
+void seccomp_add_bpf_rule(struct sock_filter *filter, unsigned int
syscall,
+ unsigned int rule, unsigned int rules)
+{
+
+ /* Adds the appropriate rule to the filter list
+ * Second last rule is default action
+ * Last rule is opposite of default action
+ */
+
+ unsigned int opp_rule = rules - rule - 2;
+
+ /* If syscall matches then jump to opposing rule, else continue */
+ filter[rule] = (struct sock_filter)
+ BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, syscall, opp_rule, 0);
+}
+
+void append_seccomp_default_vfs_filters(struct sock_filter *filter,
+ unsigned int rule,
+ unsigned int def_action,
+ unsigned int def_return)
+{
+ /* Add default rule at index rule, opposite rule at index rule+1 */
+ rule++;
+ if (def_action) {
+ filter[rule] = (struct sock_filter)SECCOMP_FILTER_ALLOW;
+ if (def_return)
+ filter[rule+1] = (struct sock_filter)
+ SECCOMP_FILTER_KILL;
+ else
+ filter[rule+1] = (struct sock_filter)
+ SECCOMP_FILTER_DENY;
+ } else {
+ if (def_return)
+ filter[rule] = (struct sock_filter)SECCOMP_FILTER_KILL;
+ else
+ filter[rule] = (struct sock_filter)SECCOMP_FILTER_DENY;
+ filter[rule+1] = (struct sock_filter)SECCOMP_FILTER_ALLOW;
+ }
+}
+
+int append_seccomp_from_vfs(struct linux_binprm *bprm)
+{
+ unsigned int i = (unsigned int)SECCOMP_XATTR_BITMAP_START;
+ unsigned int rules = 1; /* There is 1 starting rule */
+ unsigned int rule = 0;
+ unsigned int bit;
+ unsigned int byte;
+ unsigned char curr_byte;
+ unsigned int def_action;
+ unsigned int def_return;
+ unsigned int curr_action;
+ unsigned int loop_mode = 1;
+ int rc = 0;
+ struct sock_filter *filter;
+ struct sock_fprog fprog;
+ unsigned char *bitmap = kmalloc(SECCOMP_XATTR_LEN * sizeof(*bitmap),
+ GFP_KERNEL);
+ if (!bitmap)
+ return -ENOMEM;
+ if (get_seccomp_xattr_from_vfs(bprm, bitmap)) {
+ /* Doesn't matter if nothing returned */
+ goto out;
+ }
+
+ if (!(bitmap[0] & (1 << SECCOMP_XATTR_BIT_EN)))
+ /* Seccomp extended attribute is disabled */
+ goto out;
+
+ /* Isolate default and return bits */
+ def_action = (unsigned int)((bitmap[0] &
+ (1 << SECCOMP_XATTR_BIT_DEF_ACTION))
+ >> SECCOMP_XATTR_BIT_DEF_ACTION);
+ def_return = (unsigned int)((bitmap[0] &
+ (1 << SECCOMP_XATTR_BIT_DEF_RETURN))
+ >> SECCOMP_XATTR_BIT_DEF_RETURN);
+
+ while (i != SECCOMP_XATTR_LEN * 8) {
+ bit = i % 8;
+ byte = i / 8;
+ curr_byte = bitmap[byte];
+ curr_action = (unsigned int) ((curr_byte >> bit) & 0x01);
+
+ if ((bit == 0) && (
+ (def_action && ((0xFF ^ curr_byte) == 0)) ||
+ ((def_action == 0) && (curr_byte == 0))
+ )) {
+ /* All byte aligned bits match default action */
+ /* Skip checking these bits */
+ i = i + 8;
+ }
+
+ if (curr_action != def_action) {
+ if (loop_mode) {
+ /* Count the number of set bits */
+ rules++;
+ } else {
+ rule++;
+ seccomp_add_bpf_rule(filter,
+ i-SECCOMP_XATTR_BITMAP_START, rule, rules);
+ }
+ }
+
+ i++;
+ if (i >= SECCOMP_XATTR_LEN * 8) {
+ if (loop_mode) {
+ /* Go through the loop again, adding filters */
+ loop_mode = 0;
+ i = (unsigned int)SECCOMP_XATTR_BITMAP_START;
+ /* Add allow/deny rules */
+ rules = rules + 2;
+ filter = kmalloc(rules * sizeof(*filter),
+ GFP_KERNEL);
+ if (!filter) {
+ rc = -ENOMEM;
+ goto out;
+ }
+ filter[0] = (struct sock_filter)
+ SECCOMP_FILTER_LOAD_SYSCALL;
+ } else {
+ break;
+ }
+ }
+ }
+
+ append_seccomp_default_vfs_filters(filter, rule, def_action,
+ def_return);
+ fprog.len = rules;
+ fprog.filter = filter;
+ rc = seccomp_attach_filter(&fprog, 1);
+ kfree(filter);
+out:
+ kfree(bitmap);
+ return rc;
+}
--
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