[PATCH net v3 4/4] selftests: net: add devmem RX and TX netdev unregister tests

[Mina Almasry <almasrymina@google.com>]

Add devmem_bind_rx_unregister_check and devmem_bind_tx_unregister_check
to nl_netdev.py to verify that unregistering a netdevsim device while a
netlink socket holds an active RX or TX devmem binding synchronously
detaches the dma_buf attachment and cleanly closes the netlink socket
without use-after-free or page faults.

Add the dma-buf, udmabuf and devmem options the tests need to
tools/testing/selftests/net/config.

Cc: Tariq Toukan <tariqt@nvidia.com>
Cc: Kaifeng Wang <kaifengw@google.com>
Assisted-by: LLM
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Dragos Tatulea <dtatulea@nvidia.com>
---
v3:
- Count attachments of the test's own dma-buf only, and skip instead of
  passing when debugfs bufinfo is not readable (Sashiko).
- Close the netlink socket after removing the device, clean up with
  defer(), and skip on EOPNOTSUPP from bind-rx/bind-tx (Sashiko).
- Replace the hardcoded UDMABUF_CREATE value with a helper that computes
  it for the running architecture (Sashiko, Dragos), and close the memfd
  and /dev/udmabuf fds on errors (Sashiko).
- Add the needed options to tools/testing/selftests/net/config (Sashiko).
---
 tools/testing/selftests/net/config       |   4 +
 tools/testing/selftests/net/nl_netdev.py | 125 ++++++++++++++++++++++-
 2 files changed, 126 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/net/config b/tools/testing/selftests/net/config
index 737e7e6327b37..1e21f0055a2c0 100644
--- a/tools/testing/selftests/net/config
+++ b/tools/testing/selftests/net/config
@@ -11,6 +11,7 @@ CONFIG_CRYPTO_ARIA=y
 CONFIG_CRYPTO_CHACHA20POLY1305=m
 CONFIG_CRYPTO_SHA1=y
 CONFIG_CRYPTO_SM4_GENERIC=y
+CONFIG_DEBUG_FS=y
 CONFIG_DEBUG_INFO_BTF=y
 CONFIG_DEBUG_INFO_BTF_MODULES=n
 CONFIG_DUMMY=y
@@ -76,6 +77,7 @@ CONFIG_NET_CLS_BPF=m
 CONFIG_NET_CLS_FLOWER=m
 CONFIG_NET_CLS_MATCHALL=m
 CONFIG_NET_CLS_U32=m
+CONFIG_NET_DEVMEM=y
 CONFIG_NETDEVSIM=m
 CONFIG_NET_DROP_MONITOR=m
 CONFIG_NETFILTER=y
@@ -120,6 +122,7 @@ CONFIG_OPENVSWITCH=m
 CONFIG_PAGE_POOL_STATS=y
 CONFIG_PSAMPLE=m
 CONFIG_RPS=y
+CONFIG_SYNC_FILE=y
 CONFIG_SYN_COOKIES=y
 CONFIG_SYSCTL=y
 CONFIG_SYSFS=y
@@ -131,6 +134,7 @@ CONFIG_TEST_BPF=m
 CONFIG_TLS=m
 CONFIG_TRACEPOINTS=y
 CONFIG_TUN=y
+CONFIG_UDMABUF=y
 CONFIG_USER_NS=y
 CONFIG_VETH=y
 CONFIG_VLAN_8021Q=y
diff --git a/tools/testing/selftests/net/nl_netdev.py b/tools/testing/selftests/net/nl_netdev.py
index ceb44c8e1fec5..988878b71358c 100755
--- a/tools/testing/selftests/net/nl_netdev.py
+++ b/tools/testing/selftests/net/nl_netdev.py
@@ -6,10 +6,14 @@ Tests for the netdev netlink family.
 """
 
 import errno
+import fcntl
+import mmap
+import os
+import struct
 from os import system
-from lib.py import ksft_run, ksft_exit
+from lib.py import ksft_run, ksft_exit, KsftFailEx, KsftSkipEx
 from lib.py import ksft_eq, ksft_ge, ksft_ne, ksft_raises, ksft_busy_wait
-from lib.py import NetdevFamily, NetdevSimDev, NlError, defer, ip
+from lib.py import EthtoolFamily, NetdevFamily, NetdevSimDev, NlError, defer, ip
 
 
 def empty_check(nf) -> None:
@@ -366,6 +370,119 @@ def page_pool_stats_ifindex_check(nf) -> None:
     ksft_eq(cm.exception.nl_msg.extack['bad-attr'], '.info.id')
 
 
+def _udmabuf_create_ioctl() -> int:
+    """Return UDMABUF_CREATE, _IOW('u', 0x42, struct udmabuf_create)."""
+    machine = os.uname().machine
+    if machine.startswith(("alpha", "mips", "ppc", "powerpc", "sparc")):
+        ioc_write = 4 << 29
+    elif machine.startswith("parisc"):
+        ioc_write = 2 << 30
+    else:
+        ioc_write = 1 << 30
+    return ioc_write | 24 << 16 | ord("u") << 8 | 0x42
+
+
+def _create_udmabuf(num_pages=64) -> int:
+    """Create a sealed memfd-backed udmabuf fd for devmem tests."""
+    if not os.path.exists("/dev/udmabuf"):
+        raise KsftSkipEx("/dev/udmabuf is not available")
+
+    size = num_pages * mmap.PAGESIZE
+    memfd = os.memfd_create("devmem-ksft", os.MFD_ALLOW_SEALING)
+    try:
+        os.ftruncate(memfd, size)
+        fcntl.fcntl(memfd, fcntl.F_ADD_SEALS, fcntl.F_SEAL_SHRINK)
+        devfd = os.open("/dev/udmabuf", os.O_RDWR)
+        try:
+            req = bytearray(struct.pack("IIQQ", memfd, 0, 0, size))
+            return fcntl.ioctl(devfd, _udmabuf_create_ioctl(), req)
+        finally:
+            os.close(devfd)
+    finally:
+        os.close(memfd)
+
+
+def _dmabuf_attach_count(dmabuf_fd) -> int:
+    """Return the number of devices attached to dmabuf_fd, from debugfs."""
+    path = "/sys/kernel/debug/dma_buf/bufinfo"
+    try:
+        with open(path, "r", encoding="utf-8") as f:
+            lines = f.read().splitlines()
+    except OSError as e:
+        raise KsftSkipEx(f"{path} is not readable: {e}") from e
+
+    ino = os.fstat(dmabuf_fd).st_ino
+    found = False
+    for line in lines:
+        fields = line.split("\t")
+        if not found:
+            found = (len(fields) == 7 and fields[5].isdigit() and
+                     int(fields[5]) == ino)
+        elif line.startswith("Total "):
+            return int(line.split()[1])
+    raise KsftFailEx(f"dma-buf {ino} not found in {path}")
+
+
+def _devmem_bind(bind, attrs) -> None:
+    """Run a devmem bind op, skip the test if the device can't do devmem."""
+    try:
+        bind(attrs)
+    except NlError as e:
+        if e.error == errno.EOPNOTSUPP:
+            raise KsftSkipEx(f"devmem binding not supported: {e}") from e
+        raise
+
+
+def devmem_bind_rx_unregister_check(_nf) -> None:
+    """Verify RX devmem bindings detach dma_buf synchronously on netdev unregister."""
+    dmabuf_fd = _create_udmabuf()
+    defer(os.close, dmabuf_fd)
+    nf_priv = NetdevFamily()
+    defer(nf_priv.close)
+    nsimdev = NetdevSimDev(queue_count=2)
+    defer(nsimdev.remove)
+    nsim = nsimdev.nsims[0]
+
+    ip(f"link set dev {nsim.ifname} up")
+    with EthtoolFamily() as ef:
+        ef.rings_set({"header": {"dev-index": nsim.ifindex},
+                      "tcp-data-split": "enabled"})
+    _devmem_bind(nf_priv.bind_rx, {
+        "ifindex": nsim.ifindex,
+        "fd": dmabuf_fd,
+        "queues": [{"id": 1, "type": "rx"}],
+    })
+    ksft_ge(_dmabuf_attach_count(dmabuf_fd), 1)
+
+    nsimdev.remove()
+    ksft_eq(_dmabuf_attach_count(dmabuf_fd), 0)
+
+    nf_priv.close()
+
+
+def devmem_bind_tx_unregister_check(_nf) -> None:
+    """Verify TX devmem bindings detach cleanly on netdev unregister without UAF."""
+    dmabuf_fd = _create_udmabuf()
+    defer(os.close, dmabuf_fd)
+    nf_priv = NetdevFamily()
+    defer(nf_priv.close)
+    nsimdev = NetdevSimDev(queue_count=2)
+    defer(nsimdev.remove)
+    nsim = nsimdev.nsims[0]
+
+    ip(f"link set dev {nsim.ifname} up")
+    _devmem_bind(nf_priv.bind_tx, {
+        "ifindex": nsim.ifindex,
+        "fd": dmabuf_fd,
+    })
+    ksft_ge(_dmabuf_attach_count(dmabuf_fd), 1)
+
+    nsimdev.remove()
+    ksft_eq(_dmabuf_attach_count(dmabuf_fd), 0)
+
+    nf_priv.close()
+
+
 def main() -> None:
     """ Ksft boiler plate main """
     nf = NetdevFamily()
@@ -379,7 +496,9 @@ def main() -> None:
               page_pool_check,
               page_pool_dump_ifindex,
               page_pool_ifindex_leak_check,
-              page_pool_stats_ifindex_check
+              page_pool_stats_ifindex_check,
+              devmem_bind_rx_unregister_check,
+              devmem_bind_tx_unregister_check
               ],
              args=(nf, ))
     ksft_exit()
-- 
2.56.0.176.g3575e65682-goog