[PATCH net v2 0/4] tun: fix re-attaching the socket filter

[Rongguang Wei <clementwei90@163.com>]

From: Rongguang Wei <weirongguang@kylinos.cn>

This is v2 of the series that fixes attaching a queue to a TAP device which
re-installs the socket filter of a persistent device.

Patch 1 fixes an inverted error check in tun_attach(): a successful
re-attach returned early, so the queue was never published in
tun->tfiles[] while TUNSETIFF still reported success.  A failed re-attach
now aborts the attach, and the filter is detached again if a later step of
the attach fails.

Patch 2 adds sk_attach_filter_kern(), the kernel memory counterpart of
sk_attach_filter().

Patch 3 uses it to install a copy of the program that the kernel holds,
instead of reading tun->fprog from user space again on every later attach.
That is the second issue reported in the review of v1, fixed here together
with patch 1 as the review asked; IFF_NOFILTER keeps working and is no
longer needed as a workaround.

Patch 4 adds the selftest that a queue re-attached after the buffer the
program was copied from was made unreadable, a rejected TUNATTACHFILTER
that has to keep the saved descriptor, and attaching a queue without a
filter.

Rongguang Wei (4):
  tun: fix inverted error check when re-attaching the filter
  net: filter: add sk_attach_filter_kern() function
  tun: keep a kernel copy of the socket filter program
  selftests: net: add TAP socket filter attach tests

---
v2:
  - roll back the filter attach when a later step of tun_attach() fails
  - keep a copy of the program in the kernel, so that a later attach does
    not depend on the address space of the process that set the filter
  - add selftests for the re-attach and for a rejected TUNATTACHFILTER,
    without patch 3, two of them fail.
v1:
  - https://lore.kernel.org/netdev/20260923025653.59348-1-clementwei90@163.com/
---
 drivers/net/tun.c                 |  50 +++++++++-
 include/linux/filter.h            |   1 +
 net/core/filter.c                 |  22 +++++
 tools/testing/selftests/net/tun.c | 159 ++++++++++++++++++++++++++++++
 4 files changed, 227 insertions(+), 5 deletions(-)

-- 
2.43.0


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