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From:   Hengqi Chen <hengqi.chen@gmail.com>
To:     linux-kernel@vger.kernel.org, bpf@vger.kernel.org
Cc:     keescook@chromium.org, ast@kernel.org, daniel@iogearbox.net,
        andrii@kernel.org, luto@amacapital.net, wad@chromium.org,
        alexyonghe@tencent.com, hengqi.chen@gmail.com
Subject: [PATCH 1/4] seccomp: Refactor filter copy/create for reuse
Date:   Mon,  9 Oct 2023 12:40:43 +0000
Message-Id: <20231009124046.74710-2-hengqi.chen@gmail.com>
In-Reply-To: <20231009124046.74710-1-hengqi.chen@gmail.com>
References: <20231009124046.74710-1-hengqi.chen@gmail.com>
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This extracts two helpers for reuse in subsequent additions.
No functional change intended, just a prep work.

Signed-off-by: Hengqi Chen <hengqi.chen@gmail.com>
---
 kernel/seccomp.c | 76 ++++++++++++++++++++++++++++++++++--------------
 1 file changed, 54 insertions(+), 22 deletions(-)

diff --git a/kernel/seccomp.c b/kernel/seccomp.c
index 255999ba9190..37490497f687 100644
--- a/kernel/seccomp.c
+++ b/kernel/seccomp.c
@@ -640,14 +640,14 @@ static inline void seccomp_sync_threads(unsigned long flags)
 }
 
 /**
- * seccomp_prepare_filter: Prepares a seccomp filter for use.
- * @fprog: BPF program to install
+ * seccomp_prepare_prog - prepares a JITed BPF filter for use.
+ * @pfp: the unattached filter that is created
+ * @fprog: the filter program
  *
- * Returns filter on success or an ERR_PTR on failure.
+ * Returns 0 on success and non-zero otherwise.
  */
-static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
+static int seccomp_prepare_prog(struct bpf_prog **pfp, struct sock_fprog *fprog)
 {
-	struct seccomp_filter *sfilter;
 	int ret;
 	const bool save_orig =
 #if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH_NATIVE)
@@ -657,10 +657,28 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 #endif
 
 	if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
-		return ERR_PTR(-EINVAL);
+		return -EINVAL;
 
 	BUG_ON(INT_MAX / fprog->len < sizeof(struct sock_filter));
 
+	ret = bpf_prog_create_from_user(pfp, fprog, seccomp_check_filter, save_orig);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+/**
+ * seccomp_prepare_filter: Prepares a seccomp filter for use.
+ * @fprog: BPF program to install
+ *
+ * Returns filter on success or an ERR_PTR on failure.
+ */
+static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
+{
+	struct seccomp_filter *sfilter;
+	int ret;
+
 	/*
 	 * Installing a seccomp filter requires that the task has
 	 * CAP_SYS_ADMIN in its namespace or be running with no_new_privs.
@@ -677,8 +695,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 		return ERR_PTR(-ENOMEM);
 
 	mutex_init(&sfilter->notify_lock);
-	ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
-					seccomp_check_filter, save_orig);
+	ret = seccomp_prepare_prog(&sfilter->prog, fprog);
 	if (ret < 0) {
 		kfree(sfilter);
 		return ERR_PTR(ret);
@@ -692,31 +709,46 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
 }
 
 /**
- * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
+ * seccomp_copy_user_filter - copies a user-supplied sock_fprog
  * @user_filter: pointer to the user data containing a sock_fprog.
+ * @fprog: pointer to store the copied BPF program
  *
  * Returns 0 on success and non-zero otherwise.
  */
-static struct seccomp_filter *
-seccomp_prepare_user_filter(const char __user *user_filter)
+static int seccomp_copy_user_filter(const char __user *user_filter, struct sock_fprog *fprog)
 {
-	struct sock_fprog fprog;
-	struct seccomp_filter *filter = ERR_PTR(-EFAULT);
-
 #ifdef CONFIG_COMPAT
 	if (in_compat_syscall()) {
 		struct compat_sock_fprog fprog32;
 		if (copy_from_user(&fprog32, user_filter, sizeof(fprog32)))
-			goto out;
-		fprog.len = fprog32.len;
-		fprog.filter = compat_ptr(fprog32.filter);
+			return -EFAULT;
+		fprog->len = fprog32.len;
+		fprog->filter = compat_ptr(fprog32.filter);
 	} else /* falls through to the if below. */
 #endif
-	if (copy_from_user(&fprog, user_filter, sizeof(fprog)))
-		goto out;
-	filter = seccomp_prepare_filter(&fprog);
-out:
-	return filter;
+	if (copy_from_user(fprog, user_filter, sizeof(*fprog)))
+		return -EFAULT;
+
+	return 0;
+}
+
+/**
+ * seccomp_prepare_user_filter - prepares a user-supplied sock_fprog
+ * @user_filter: pointer to the user data containing a sock_fprog.
+ *
+ * Returns filter on success or an ERR_PTR on failure.
+ */
+static struct seccomp_filter *
+seccomp_prepare_user_filter(const char __user *user_filter)
+{
+	struct sock_fprog fprog;
+	int ret;
+
+	ret = seccomp_copy_user_filter(user_filter, &fprog);
+	if (ret)
+		return ERR_PTR(ret);
+
+	return seccomp_prepare_filter(&fprog);
 }
 
 #ifdef SECCOMP_ARCH_NATIVE
-- 
2.34.1