1. 28 Feb, 2020 3 commits
    • Gustavo A. R. Silva's avatar
      net: dccp: Replace zero-length array with flexible-array member · 8402a31d
      Gustavo A. R. Silva authored
      The current codebase makes use of the zero-length array language
      extension to the C90 standard, but the preferred mechanism to declare
      variable-length types such as these ones is a flexible array member[1][2],
      introduced in C99:
      
      struct foo {
              int stuff;
              struct boo array[];
      };
      
      By making use of the mechanism above, we will get a compiler warning
      in case the flexible array does not occur last in the structure, which
      will help us prevent some kind of undefined behavior bugs from being
      inadvertently introduced[3] to the codebase from now on.
      
      Also, notice that, dynamic memory allocations won't be affected by
      this change:
      
      "Flexible array members have incomplete type, and so the sizeof operator
      may not be applied. As a quirk of the original implementation of
      zero-length arrays, sizeof evaluates to zero."[1]
      
      This issue was found with the help of Coccinelle.
      
      [1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
      [2] https://github.com/KSPP/linux/issues/21
      [3] commit 76497732 ("cxgb3/l2t: Fix undefined behaviour")
      Signed-off-by: default avatarGustavo A. R. Silva <gustavo@embeddedor.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      8402a31d
    • Martin KaFai Lau's avatar
      inet_diag: Move the INET_DIAG_REQ_BYTECODE nlattr to cb->data · 0df6d328
      Martin KaFai Lau authored
      The INET_DIAG_REQ_BYTECODE nlattr is currently re-found every time when
      the "dump()" is re-started.
      
      In a latter patch, it will also need to parse the new
      INET_DIAG_REQ_SK_BPF_STORAGES nlattr to learn the map_fds. Thus, this
      patch takes this chance to store the parsed nlattr in cb->data
      during the "start" time of a dump.
      
      By doing this, the "bc" argument also becomes unnecessary
      and is removed.  Also, the two copies of the INET_DIAG_REQ_BYTECODE
      parsing-audit logic between compat/current version can be
      consolidated to one.
      Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
      Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      Acked-by: default avatarSong Liu <songliubraving@fb.com>
      Link: https://lore.kernel.org/bpf/20200225230415.1975555-1-kafai@fb.com
      0df6d328
    • Martin KaFai Lau's avatar
      inet_diag: Refactor inet_sk_diag_fill(), dump(), and dump_one() · 5682d393
      Martin KaFai Lau authored
      In a latter patch, there is a need to update "cb->min_dump_alloc"
      in inet_sk_diag_fill() as it learns the diffierent bpf_sk_storages
      stored in a sk while dumping all sk(s) (e.g. tcp_hashinfo).
      
      The inet_sk_diag_fill() currently does not take the "cb" as an argument.
      One of the reason is inet_sk_diag_fill() is used by both dump_one()
      and dump() (which belong to the "struct inet_diag_handler".  The dump_one()
      interface does not pass the "cb" along.
      
      This patch is to make dump_one() pass a "cb".  The "cb" is created in
      inet_diag_cmd_exact().  The "nlh" and "in_skb" are stored in "cb" as
      the dump() interface does.  The total number of args in
      inet_sk_diag_fill() is also cut from 10 to 7 and
      that helps many callers to pass fewer args.
      
      In particular,
      "struct user_namespace *user_ns", "u32 pid", and "u32 seq"
      can be replaced by accessing "cb->nlh" and "cb->skb".
      
      A similar argument reduction is also made to
      inet_twsk_diag_fill() and inet_req_diag_fill().
      
      inet_csk_diag_dump() and inet_csk_diag_fill() are also removed.
      They are mostly equivalent to inet_sk_diag_fill().  Their repeated
      usages are very limited.  Thus, inet_sk_diag_fill() is directly used
      in those occasions.
      Signed-off-by: default avatarMartin KaFai Lau <kafai@fb.com>
      Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
      Acked-by: default avatarSong Liu <songliubraving@fb.com>
      Link: https://lore.kernel.org/bpf/20200225230409.1975173-1-kafai@fb.com
      5682d393
  2. 24 Feb, 2020 1 commit
  3. 09 Dec, 2019 1 commit
  4. 04 Dec, 2019 1 commit
  5. 07 Nov, 2019 1 commit
  6. 04 Nov, 2019 1 commit
  7. 01 Nov, 2019 1 commit
    • Eric Dumazet's avatar
      inet: stop leaking jiffies on the wire · a904a069
      Eric Dumazet authored
      Historically linux tried to stick to RFC 791, 1122, 2003
      for IPv4 ID field generation.
      
      RFC 6864 made clear that no matter how hard we try,
      we can not ensure unicity of IP ID within maximum
      lifetime for all datagrams with a given source
      address/destination address/protocol tuple.
      
      Linux uses a per socket inet generator (inet_id), initialized
      at connection startup with a XOR of 'jiffies' and other
      fields that appear clear on the wire.
      
      Thiemo Nagel pointed that this strategy is a privacy
      concern as this provides 16 bits of entropy to fingerprint
      devices.
      
      Let's switch to a random starting point, this is just as
      good as far as RFC 6864 is concerned and does not leak
      anything critical.
      
      Fixes: 1da177e4 ("Linux-2.6.12-rc2")
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Reported-by: default avatarThiemo Nagel <tnagel@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      a904a069
  8. 01 Oct, 2019 1 commit
    • Florian Westphal's avatar
      netfilter: drop bridge nf reset from nf_reset · 895b5c9f
      Florian Westphal authored
      commit 174e2381
      ("sk_buff: drop all skb extensions on free and skb scrubbing") made napi
      recycle always drop skb extensions.  The additional skb_ext_del() that is
      performed via nf_reset on napi skb recycle is not needed anymore.
      
      Most nf_reset() calls in the stack are there so queued skb won't block
      'rmmod nf_conntrack' indefinitely.
      
      This removes the skb_ext_del from nf_reset, and renames it to a more
      fitting nf_reset_ct().
      
      In a few selected places, add a call to skb_ext_reset to make sure that
      no active extensions remain.
      
      I am submitting this for "net", because we're still early in the release
      cycle.  The patch applies to net-next too, but I think the rename causes
      needless divergence between those trees.
      Suggested-by: default avatarEric Dumazet <edumazet@google.com>
      Signed-off-by: default avatarFlorian Westphal <fw@strlen.de>
      Signed-off-by: default avatarPablo Neira Ayuso <pablo@netfilter.org>
      895b5c9f
  9. 27 Sep, 2019 1 commit
  10. 19 Jul, 2019 1 commit
  11. 09 Jul, 2019 1 commit
    • Willem de Bruijn's avatar
      ipv6: elide flowlabel check if no exclusive leases exist · 59c820b2
      Willem de Bruijn authored
      Processes can request ipv6 flowlabels with cmsg IPV6_FLOWINFO.
      If not set, by default an autogenerated flowlabel is selected.
      
      Explicit flowlabels require a control operation per label plus a
      datapath check on every connection (every datagram if unconnected).
      This is particularly expensive on unconnected sockets multiplexing
      many flows, such as QUIC.
      
      In the common case, where no lease is exclusive, the check can be
      safely elided, as both lease request and check trivially succeed.
      Indeed, autoflowlabel does the same even with exclusive leases.
      
      Elide the check if no process has requested an exclusive lease.
      
      fl6_sock_lookup previously returns either a reference to a lease or
      NULL to denote failure. Modify to return a real error and update
      all callers. On return NULL, they can use the label and will elide
      the atomic_dec in fl6_sock_release.
      
      This is an optimization. Robust applications still have to revert to
      requesting leases if the fast path fails due to an exclusive lease.
      
      Changes RFC->v1:
        - use static_key_false_deferred to rate limit jump label operations
          - call static_key_deferred_flush to stop timers on exit
        - move decrement out of RCU context
        - defer optimization also if opt data is associated with a lease
        - updated all fp6_sock_lookup callers, not just udp
      Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      59c820b2
  12. 19 Jun, 2019 1 commit
  13. 05 Jun, 2019 2 commits
  14. 30 May, 2019 2 commits
  15. 24 May, 2019 1 commit
  16. 21 May, 2019 1 commit
  17. 12 May, 2019 1 commit
  18. 19 Apr, 2019 1 commit
  19. 02 Apr, 2019 1 commit
  20. 19 Mar, 2019 1 commit
  21. 01 Feb, 2019 1 commit
    • Eric Dumazet's avatar
      dccp: fool proof ccid_hc_[rt]x_parse_options() · 9b1f19d8
      Eric Dumazet authored
      Similarly to commit 276bdb82 ("dccp: check ccid before dereferencing")
      it is wise to test for a NULL ccid.
      
      kasan: CONFIG_KASAN_INLINE enabled
      kasan: GPF could be caused by NULL-ptr deref or user memory access
      general protection fault: 0000 [#1] PREEMPT SMP KASAN
      CPU: 1 PID: 16 Comm: ksoftirqd/1 Not tainted 5.0.0-rc3+ #37
      Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
      RIP: 0010:ccid_hc_tx_parse_options net/dccp/ccid.h:205 [inline]
      RIP: 0010:dccp_parse_options+0x8d9/0x12b0 net/dccp/options.c:233
      Code: c5 0f b6 75 b3 80 38 00 0f 85 d6 08 00 00 48 b9 00 00 00 00 00 fc ff df 48 8b 45 b8 4c 8b b8 f8 07 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 08 00 0f 85 95 08 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b
      kobject: 'loop5' (0000000080f78fc1): kobject_uevent_env
      RSP: 0018:ffff8880a94df0b8 EFLAGS: 00010246
      RAX: 0000000000000000 RBX: ffff8880858ac723 RCX: dffffc0000000000
      RDX: 0000000000000100 RSI: 0000000000000007 RDI: 0000000000000001
      RBP: ffff8880a94df140 R08: 0000000000000001 R09: ffff888061b83a80
      R10: ffffed100c370752 R11: ffff888061b83a97 R12: 0000000000000026
      R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
      FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007f0defa33518 CR3: 000000008db5e000 CR4: 00000000001406e0
      kobject: 'loop5' (0000000080f78fc1): fill_kobj_path: path = '/devices/virtual/block/loop5'
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      Call Trace:
       dccp_rcv_state_process+0x2b6/0x1af6 net/dccp/input.c:654
       dccp_v4_do_rcv+0x100/0x190 net/dccp/ipv4.c:688
       sk_backlog_rcv include/net/sock.h:936 [inline]
       __sk_receive_skb+0x3a9/0xea0 net/core/sock.c:473
       dccp_v4_rcv+0x10cb/0x1f80 net/dccp/ipv4.c:880
       ip_protocol_deliver_rcu+0xb6/0xa20 net/ipv4/ip_input.c:208
       ip_local_deliver_finish+0x23b/0x390 net/ipv4/ip_input.c:234
       NF_HOOK include/linux/netfilter.h:289 [inline]
       NF_HOOK include/linux/netfilter.h:283 [inline]
       ip_local_deliver+0x1f0/0x740 net/ipv4/ip_input.c:255
       dst_input include/net/dst.h:450 [inline]
       ip_rcv_finish+0x1f4/0x2f0 net/ipv4/ip_input.c:414
       NF_HOOK include/linux/netfilter.h:289 [inline]
       NF_HOOK include/linux/netfilter.h:283 [inline]
       ip_rcv+0xed/0x620 net/ipv4/ip_input.c:524
       __netif_receive_skb_one_core+0x160/0x210 net/core/dev.c:4973
       __netif_receive_skb+0x2c/0x1c0 net/core/dev.c:5083
       process_backlog+0x206/0x750 net/core/dev.c:5923
       napi_poll net/core/dev.c:6346 [inline]
       net_rx_action+0x76d/0x1930 net/core/dev.c:6412
       __do_softirq+0x30b/0xb11 kernel/softirq.c:292
       run_ksoftirqd kernel/softirq.c:654 [inline]
       run_ksoftirqd+0x8e/0x110 kernel/softirq.c:646
       smpboot_thread_fn+0x6ab/0xa10 kernel/smpboot.c:164
       kthread+0x357/0x430 kernel/kthread.c:246
       ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:352
      Modules linked in:
      ---[ end trace 58a0ba03bea2c376 ]---
      RIP: 0010:ccid_hc_tx_parse_options net/dccp/ccid.h:205 [inline]
      RIP: 0010:dccp_parse_options+0x8d9/0x12b0 net/dccp/options.c:233
      Code: c5 0f b6 75 b3 80 38 00 0f 85 d6 08 00 00 48 b9 00 00 00 00 00 fc ff df 48 8b 45 b8 4c 8b b8 f8 07 00 00 4c 89 f8 48 c1 e8 03 <80> 3c 08 00 0f 85 95 08 00 00 48 b8 00 00 00 00 00 fc ff df 4d 8b
      RSP: 0018:ffff8880a94df0b8 EFLAGS: 00010246
      RAX: 0000000000000000 RBX: ffff8880858ac723 RCX: dffffc0000000000
      RDX: 0000000000000100 RSI: 0000000000000007 RDI: 0000000000000001
      RBP: ffff8880a94df140 R08: 0000000000000001 R09: ffff888061b83a80
      R10: ffffed100c370752 R11: ffff888061b83a97 R12: 0000000000000026
      R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000000
      FS:  0000000000000000(0000) GS:ffff8880ae700000(0000) knlGS:0000000000000000
      CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
      CR2: 00007f0defa33518 CR3: 0000000009871000 CR4: 00000000001406e0
      DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
      DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
      Cc: Gerrit Renker <gerrit@erg.abdn.ac.uk>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      9b1f19d8
  22. 27 Jan, 2019 1 commit
  23. 28 Dec, 2018 2 commits
  24. 24 Dec, 2018 1 commit
    • Peter Oskolkov's avatar
      net: dccp: fix kernel crash on module load · c92c81df
      Peter Oskolkov authored
      Patch eedbbb0d "net: dccp: initialize (addr,port) ..."
      added calling to inet_hashinfo2_init() from dccp_init().
      
      However, inet_hashinfo2_init() is marked as __init(), and
      thus the kernel panics when dccp is loaded as module. Removing
      __init() tag from inet_hashinfo2_init() is not feasible because
      it calls into __init functions in mm.
      
      This patch adds inet_hashinfo2_init_mod() function that can
      be called after the init phase is done; changes dccp_init() to
      call the new function; un-marks inet_hashinfo2_init() as
      exported.
      
      Fixes: eedbbb0d ("net: dccp: initialize (addr,port) ...")
      Reported-by: default avatarkernel test robot <lkp@intel.com>
      Signed-off-by: default avatarPeter Oskolkov <posk@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      c92c81df
  25. 18 Dec, 2018 1 commit
    • Peter Oskolkov's avatar
      net: dccp: initialize (addr,port) listening hashtable · eedbbb0d
      Peter Oskolkov authored
      Commit d9fbc7f6 "net: tcp: prefer listeners bound to an address"
      removes port-only listener lookups. This caused segfaults in DCCP
      lookups because DCCP did not initialize the (addr,port) hashtable.
      
      This patch adds said initialization.
      
      The only non-trivial issue here is the size of the new hashtable.
      It seemed reasonable to make it match the size of the port-only
      hashtable (= INET_LHTABLE_SIZE) that was used previously. Other
      parameters to inet_hashinfo2_init() match those used in TCP.
      
      V2 changes: marked inet_hashinfo2_init as an exported symbol
      so that DCCP compiles when configured as a module.
      
      Tested: syzcaller issues fixed; the second patch in the patchset
              tests that DCCP lookups work correctly.
      
      Fixes: d9fbc7f6 "net: tcp: prefer listeners bound to an address"
      Reported-by: default avatarsyzcaller <syzkaller@googlegroups.com>
      Signed-off-by: default avatarPeter Oskolkov <posk@google.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      eedbbb0d
  26. 16 Dec, 2018 2 commits
  27. 09 Nov, 2018 1 commit
    • Stefano Brivio's avatar
      net: Convert protocol error handlers from void to int · 32bbd879
      Stefano Brivio authored
      We'll need this to handle ICMP errors for tunnels without a sending socket
      (i.e. FoU and GUE). There, we might have to look up different types of IP
      tunnels, registered as network protocols, before we get a match, so we
      want this for the error handlers of IPPROTO_IPIP and IPPROTO_IPV6 in both
      inet_protos and inet6_protos. These error codes will be used in the next
      patch.
      
      For consistency, return sensible error codes in protocol error handlers
      whenever handlers can't handle errors because, even if valid, they don't
      match a protocol or any of its states.
      
      This has no effect on existing error handling paths.
      Signed-off-by: default avatarStefano Brivio <sbrivio@redhat.com>
      Reviewed-by: default avatarSabrina Dubroca <sd@queasysnail.net>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      32bbd879
  28. 08 Nov, 2018 1 commit
  29. 23 Oct, 2018 1 commit
    • Karsten Graul's avatar
      Revert "net: simplify sock_poll_wait" · 89ab066d
      Karsten Graul authored
      This reverts commit dd979b4d.
      
      This broke tcp_poll for SMC fallback: An AF_SMC socket establishes an
      internal TCP socket for the initial handshake with the remote peer.
      Whenever the SMC connection can not be established this TCP socket is
      used as a fallback. All socket operations on the SMC socket are then
      forwarded to the TCP socket. In case of poll, the file->private_data
      pointer references the SMC socket because the TCP socket has no file
      assigned. This causes tcp_poll to wait on the wrong socket.
      Signed-off-by: default avatarKarsten Graul <kgraul@linux.ibm.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      89ab066d
  30. 02 Oct, 2018 1 commit
  31. 01 Oct, 2018 1 commit
    • Eric Dumazet's avatar
      tcp/dccp: fix lockdep issue when SYN is backlogged · 1ad98e9d
      Eric Dumazet authored
      In normal SYN processing, packets are handled without listener
      lock and in RCU protected ingress path.
      
      But syzkaller is known to be able to trick us and SYN
      packets might be processed in process context, after being
      queued into socket backlog.
      
      In commit 06f877d6 ("tcp/dccp: fix other lockdep splats
      accessing ireq_opt") I made a very stupid fix, that happened
      to work mostly because of the regular path being RCU protected.
      
      Really the thing protecting ireq->ireq_opt is RCU read lock,
      and the pseudo request refcnt is not relevant.
      
      This patch extends what I did in commit 449809a6 ("tcp/dccp:
      block BH for SYN processing") by adding an extra rcu_read_{lock|unlock}
      pair in the paths that might be taken when processing SYN from
      socket backlog (thus possibly in process context)
      
      Fixes: 06f877d6 ("tcp/dccp: fix other lockdep splats accessing ireq_opt")
      Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
      Reported-by: default avatarsyzbot <syzkaller@googlegroups.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      1ad98e9d
  32. 07 Aug, 2018 1 commit
    • Alexey Kodanev's avatar
      dccp: fix undefined behavior with 'cwnd' shift in ccid2_cwnd_restart() · 61ef4b07
      Alexey Kodanev authored
      The shift of 'cwnd' with '(now - hc->tx_lsndtime) / hc->tx_rto' value
      can lead to undefined behavior [1].
      
      In order to fix this use a gradual shift of the window with a 'while'
      loop, similar to what tcp_cwnd_restart() is doing.
      
      When comparing delta and RTO there is a minor difference between TCP
      and DCCP, the last one also invokes dccp_cwnd_restart() and reduces
      'cwnd' if delta equals RTO. That case is preserved in this change.
      
      [1]:
      [40850.963623] UBSAN: Undefined behaviour in net/dccp/ccids/ccid2.c:237:7
      [40851.043858] shift exponent 67 is too large for 32-bit type 'unsigned int'
      [40851.127163] CPU: 3 PID: 15940 Comm: netstress Tainted: G        W   E     4.18.0-rc7.x86_64 #1
      ...
      [40851.377176] Call Trace:
      [40851.408503]  dump_stack+0xf1/0x17b
      [40851.451331]  ? show_regs_print_info+0x5/0x5
      [40851.503555]  ubsan_epilogue+0x9/0x7c
      [40851.548363]  __ubsan_handle_shift_out_of_bounds+0x25b/0x2b4
      [40851.617109]  ? __ubsan_handle_load_invalid_value+0x18f/0x18f
      [40851.686796]  ? xfrm4_output_finish+0x80/0x80
      [40851.739827]  ? lock_downgrade+0x6d0/0x6d0
      [40851.789744]  ? xfrm4_prepare_output+0x160/0x160
      [40851.845912]  ? ip_queue_xmit+0x810/0x1db0
      [40851.895845]  ? ccid2_hc_tx_packet_sent+0xd36/0x10a0 [dccp]
      [40851.963530]  ccid2_hc_tx_packet_sent+0xd36/0x10a0 [dccp]
      [40852.029063]  dccp_xmit_packet+0x1d3/0x720 [dccp]
      [40852.086254]  dccp_write_xmit+0x116/0x1d0 [dccp]
      [40852.142412]  dccp_sendmsg+0x428/0xb20 [dccp]
      [40852.195454]  ? inet_dccp_listen+0x200/0x200 [dccp]
      [40852.254833]  ? sched_clock+0x5/0x10
      [40852.298508]  ? sched_clock+0x5/0x10
      [40852.342194]  ? inet_create+0xdf0/0xdf0
      [40852.388988]  sock_sendmsg+0xd9/0x160
      ...
      
      Fixes: 113ced1f ("dccp ccid-2: Perform congestion-window validation")
      Signed-off-by: default avatarAlexey Kodanev <alexey.kodanev@oracle.com>
      Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
      61ef4b07
  33. 30 Jul, 2018 1 commit
  34. 28 Jun, 2018 1 commit
    • Linus Torvalds's avatar
      Revert changes to convert to ->poll_mask() and aio IOCB_CMD_POLL · a11e1d43
      Linus Torvalds authored
      The poll() changes were not well thought out, and completely
      unexplained.  They also caused a huge performance regression, because
      "->poll()" was no longer a trivial file operation that just called down
      to the underlying file operations, but instead did at least two indirect
      calls.
      
      Indirect calls are sadly slow now with the Spectre mitigation, but the
      performance problem could at least be largely mitigated by changing the
      "->get_poll_head()" operation to just have a per-file-descriptor pointer
      to the poll head instead.  That gets rid of one of the new indirections.
      
      But that doesn't fix the new complexity that is completely unwarranted
      for the regular case.  The (undocumented) reason for the poll() changes
      was some alleged AIO poll race fixing, but we don't make the common case
      slower and more complex for some uncommon special case, so this all
      really needs way more explanations and most likely a fundamental
      redesign.
      
      [ This revert is a revert of about 30 different commits, not reverted
        individually because that would just be unnecessarily messy  - Linus ]
      
      Cc: Al Viro <viro@zeniv.linux.org.uk>
      Cc: Christoph Hellwig <hch@lst.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      a11e1d43