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, 95 insertions, 0 deletions

diff --git a/include/net/compat.h b/include/net/compat.h
new file mode 100644
index 000000000..84c163f40
--- /dev/null
+++ b/include/net/compat.h
@@ -0,0 +1,95 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef NET_COMPAT_H
+#define NET_COMPAT_H
+
+
+struct sock;
+
+#include <linux/compat.h>
+
+struct compat_msghdr {
+	compat_uptr_t	msg_name;	/* void * */
+	compat_int_t	msg_namelen;
+	compat_uptr_t	msg_iov;	/* struct compat_iovec * */
+	compat_size_t	msg_iovlen;
+	compat_uptr_t	msg_control;	/* void * */
+	compat_size_t	msg_controllen;
+	compat_uint_t	msg_flags;
+};
+
+struct compat_mmsghdr {
+	struct compat_msghdr msg_hdr;
+	compat_uint_t        msg_len;
+};
+
+struct compat_cmsghdr {
+	compat_size_t	cmsg_len;
+	compat_int_t	cmsg_level;
+	compat_int_t	cmsg_type;
+};
+
+struct compat_rtentry {
+	u32		rt_pad1;
+	struct sockaddr rt_dst;         /* target address               */
+	struct sockaddr rt_gateway;     /* gateway addr (RTF_GATEWAY)   */
+	struct sockaddr rt_genmask;     /* target network mask (IP)     */
+	unsigned short	rt_flags;
+	short		rt_pad2;
+	u32		rt_pad3;
+	unsigned char	rt_tos;
+	unsigned char	rt_class;
+	short		rt_pad4;
+	short		rt_metric;      /* +1 for binary compatibility! */
+	compat_uptr_t	rt_dev;         /* forcing the device at add    */
+	u32		rt_mtu;         /* per route MTU/Window         */
+	u32		rt_window;      /* Window clamping              */
+	unsigned short  rt_irtt;        /* Initial RTT                  */
+};
+
+int __get_compat_msghdr(struct msghdr *kmsg, struct compat_msghdr *msg,
+			struct sockaddr __user **save_addr);
+int get_compat_msghdr(struct msghdr *, struct compat_msghdr __user *,
+		      struct sockaddr __user **, struct iovec **);
+int put_cmsg_compat(struct msghdr*, int, int, int, void *);
+
+int cmsghdr_from_user_compat_to_kern(struct msghdr *, struct sock *,
+				     unsigned char *, int);
+
+struct compat_group_req {
+	__u32				 gr_interface;
+	struct __kernel_sockaddr_storage gr_group
+		__aligned(4);
+} __packed;
+
+struct compat_group_source_req {
+	__u32				 gsr_interface;
+	struct __kernel_sockaddr_storage gsr_group
+		__aligned(4);
+	struct __kernel_sockaddr_storage gsr_source
+		__aligned(4);
+} __packed;
+
+struct compat_group_filter {
+	union {
+		struct {
+			__u32				 gf_interface_aux;
+			struct __kernel_sockaddr_storage gf_group_aux
+				__aligned(4);
+			__u32				 gf_fmode_aux;
+			__u32				 gf_numsrc_aux;
+			struct __kernel_sockaddr_storage gf_slist[1]
+				__aligned(4);
+		} __packed;
+		struct {
+			__u32				 gf_interface;
+			struct __kernel_sockaddr_storage gf_group
+				__aligned(4);
+			__u32				 gf_fmode;
+			__u32				 gf_numsrc;
+			struct __kernel_sockaddr_storage gf_slist_flex[]
+				__aligned(4);
+		} __packed;
+	};
+} __packed;
+
+#endif /* NET_COMPAT_H */