selftests/bpf: Test packet range of pointers sharing an idgrafted

Add tests where two packet pointers share an id and tightening one
pointer's umax from its var_off would put it less than their constant
distance from the other's umax: with an index & 0x38 capped at 50, the
base pointer keeps umax 50, so the pointer 8 bytes further on must keep
umax 58, even though its known bits allow at most 56.

These refused a valid program or accepted an out-of-bounds access before
the fix:

- check the advanced copy, load through the base: valid, was refused;
- check the base, load the byte at base + 1 through a copy advanced by
  8: was accepted;
- check base + 4, load 4 bytes at base + 2 through base + 8: reads two
  bytes past the checked range, was accepted;
- the same as the second with data_meta pointers checked against data:
  was accepted.

These pass with and without the fix and cover nearby paths:

- subtract an unknown scalar from a checked pointer and load below it
  (the range is kept across a new id);
- reach a load through two paths whose checks cover 8 and 7 bytes after
  the loaded pointer; the second path must not be pruned by the first;
- spill a copy of a pointer, check the pointer, fill the copy and load
  one byte past the checked range: the load is refused, and the copy
  has the range of the check.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20261001145255.855630-2-alexei.starovoitov@gmail.com
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>

1 files changed, 192 insertions, 0 deletions

diff --git a/ipc/msgutil.c b/ipc/msgutil.c
new file mode 100644
index 000000000..e28f0cecb
--- /dev/null
+++ b/ipc/msgutil.c
@@ -0,0 +1,192 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * linux/ipc/msgutil.c
+ * Copyright (C) 1999, 2004 Manfred Spraul
+ */
+
+#include <linux/spinlock.h>
+#include <linux/init.h>
+#include <linux/security.h>
+#include <linux/slab.h>
+#include <linux/ipc.h>
+#include <linux/msg.h>
+#include <linux/ipc_namespace.h>
+#include <linux/utsname.h>
+#include <linux/proc_ns.h>
+#include <linux/uaccess.h>
+#include <linux/sched.h>
+#include <linux/nstree.h>
+
+#include "util.h"
+
+DEFINE_SPINLOCK(mq_lock);
+
+/*
+ * The next 2 defines are here bc this is the only file
+ * compiled when either CONFIG_SYSVIPC and CONFIG_POSIX_MQUEUE
+ * and not CONFIG_IPC_NS.
+ */
+struct ipc_namespace init_ipc_ns = {
+	.ns = NS_COMMON_INIT(init_ipc_ns),
+	.user_ns = &init_user_ns,
+};
+
+struct msg_msgseg {
+	struct msg_msgseg *next;
+	/* the next part of the message follows immediately */
+};
+
+#define DATALEN_MSG	((size_t)PAGE_SIZE-sizeof(struct msg_msg))
+#define DATALEN_SEG	((size_t)PAGE_SIZE-sizeof(struct msg_msgseg))
+
+static kmem_buckets *msg_buckets __ro_after_init;
+
+static int __init init_msg_buckets(void)
+{
+	msg_buckets = kmem_buckets_create("msg_msg", SLAB_ACCOUNT,
+					  sizeof(struct msg_msg),
+					  DATALEN_MSG, NULL);
+
+	return 0;
+}
+subsys_initcall(init_msg_buckets);
+
+static struct msg_msg *alloc_msg(size_t len)
+{
+	struct msg_msg *msg;
+	struct msg_msgseg **pseg;
+	size_t alen;
+
+	alen = min(len, DATALEN_MSG);
+	msg = kmem_buckets_alloc(msg_buckets, sizeof(*msg) + alen, GFP_KERNEL);
+	if (msg == NULL)
+		return NULL;
+
+	msg->next = NULL;
+	msg->security = NULL;
+
+	len -= alen;
+	pseg = &msg->next;
+	while (len > 0) {
+		struct msg_msgseg *seg;
+
+		cond_resched();
+
+		alen = min(len, DATALEN_SEG);
+		seg = kmalloc(sizeof(*seg) + alen, GFP_KERNEL_ACCOUNT);
+		if (seg == NULL)
+			goto out_err;
+		*pseg = seg;
+		seg->next = NULL;
+		pseg = &seg->next;
+		len -= alen;
+	}
+
+	return msg;
+
+out_err:
+	free_msg(msg);
+	return NULL;
+}
+
+struct msg_msg *load_msg(const void __user *src, size_t len)
+{
+	struct msg_msg *msg;
+	struct msg_msgseg *seg;
+	int err = -EFAULT;
+	size_t alen;
+
+	msg = alloc_msg(len);
+	if (msg == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	alen = min(len, DATALEN_MSG);
+	if (copy_from_user(msg + 1, src, alen))
+		goto out_err;
+
+	for (seg = msg->next; seg != NULL; seg = seg->next) {
+		len -= alen;
+		src = (char __user *)src + alen;
+		alen = min(len, DATALEN_SEG);
+		if (copy_from_user(seg + 1, src, alen))
+			goto out_err;
+	}
+
+	err = security_msg_msg_alloc(msg);
+	if (err)
+		goto out_err;
+
+	return msg;
+
+out_err:
+	free_msg(msg);
+	return ERR_PTR(err);
+}
+#ifdef CONFIG_CHECKPOINT_RESTORE
+struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
+{
+	struct msg_msgseg *dst_pseg, *src_pseg;
+	size_t len = src->m_ts;
+	size_t alen;
+
+	if (src->m_ts > dst->m_ts)
+		return ERR_PTR(-EINVAL);
+
+	alen = min(len, DATALEN_MSG);
+	memcpy(dst + 1, src + 1, alen);
+
+	for (dst_pseg = dst->next, src_pseg = src->next;
+	     src_pseg != NULL;
+	     dst_pseg = dst_pseg->next, src_pseg = src_pseg->next) {
+
+		len -= alen;
+		alen = min(len, DATALEN_SEG);
+		memcpy(dst_pseg + 1, src_pseg + 1, alen);
+	}
+
+	dst->m_type = src->m_type;
+	dst->m_ts = src->m_ts;
+
+	return dst;
+}
+#else
+struct msg_msg *copy_msg(struct msg_msg *src, struct msg_msg *dst)
+{
+	return ERR_PTR(-ENOSYS);
+}
+#endif
+int store_msg(void __user *dest, struct msg_msg *msg, size_t len)
+{
+	size_t alen;
+	struct msg_msgseg *seg;
+
+	alen = min(len, DATALEN_MSG);
+	if (copy_to_user(dest, msg + 1, alen))
+		return -1;
+
+	for (seg = msg->next; seg != NULL; seg = seg->next) {
+		len -= alen;
+		dest = (char __user *)dest + alen;
+		alen = min(len, DATALEN_SEG);
+		if (copy_to_user(dest, seg + 1, alen))
+			return -1;
+	}
+	return 0;
+}
+
+void free_msg(struct msg_msg *msg)
+{
+	struct msg_msgseg *seg;
+
+	security_msg_msg_free(msg);
+
+	seg = msg->next;
+	kfree(msg);
+	while (seg != NULL) {
+		struct msg_msgseg *tmp = seg->next;
+
+		cond_resched();
+		kfree(seg);
+		seg = tmp;
+	}
+}