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A reference underflow is found in TLS handshake subsystem that causes a
direct use-after-free. Part of the crash log is like below:
[ 2.022114] ------------[ cut here ]------------
[ 2.022193] refcount_t: underflow; use-after-free.
[ 2.022288] WARNING: CPU: 0 PID: 60 at lib/refcount.c:28 refcount_warn_saturate+0xbe/0x110
[ 2.022432] Modules linked in:
[ 2.022848] RIP: 0010:refcount_warn_saturate+0xbe/0x110
[ 2.023231] RSP: 0018:ffffc900001bfe18 EFLAGS: 00000286
[ 2.023325] RAX: 0000000000000000 RBX: 0000000000000007 RCX: 00000000ffffdfff
[ 2.023438] RDX: 0000000000000000 RSI: 00000000ffffffea RDI: 0000000000000001
[ 2.023555] RBP: ffff888004c20098 R08: ffffffff82b392c8 R09: 00000000ffffdfff
[ 2.023693] R10: ffffffff82a592e0 R11: ffffffff82b092e0 R12: ffff888004c200d8
[ 2.023813] R13: 0000000000000000 R14: ffff888004c20000 R15: ffffc90000013ca8
[ 2.023930] FS: 0000000000000000(0000) GS:ffff88807dc00000(0000) knlGS:0000000000000000
[ 2.024062] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 2.024161] CR2: ffff888003601000 CR3: 0000000002a2e000 CR4: 00000000000006f0
[ 2.024275] Call Trace:
[ 2.024322] <TASK>
[ 2.024367] ? __warn+0x7f/0x130
[ 2.024430] ? refcount_warn_saturate+0xbe/0x110
[ 2.024513] ? report_bug+0x199/0x1b0
[ 2.024585] ? handle_bug+0x3c/0x70
[ 2.024676] ? exc_invalid_op+0x18/0x70
[ 2.024750] ? asm_exc_invalid_op+0x1a/0x20
[ 2.024830] ? refcount_warn_saturate+0xbe/0x110
[ 2.024916] ? refcount_warn_saturate+0xbe/0x110
[ 2.024998] __tcp_close+0x2f4/0x3d0
[ 2.025065] ? __pfx_kunit_generic_run_threadfn_adapter+0x10/0x10
[ 2.025168] tcp_close+0x1f/0x70
[ 2.025231] inet_release+0x33/0x60
[ 2.025297] sock_release+0x1f/0x80
[ 2.025361] handshake_req_cancel_test2+0x100/0x2d0
[ 2.025457] kunit_try_run_case+0x4c/0xa0
[ 2.025532] kunit_generic_run_threadfn_adapter+0x15/0x20
[ 2.025644] kthread+0xe1/0x110
[ 2.025708] ? __pfx_kthread+0x10/0x10
[ 2.025780] ret_from_fork+0x2c/0x50
One can enable CONFIG_NET_HANDSHAKE_KUNIT_TEST config to reproduce above
crash.
The root cause of this bug is that the commit 1ce77c998f
("net/handshake: Unpin sock->file if a handshake is cancelled") adds one
additional fput() function. That patch claims that the fput() is used to
enable sock->file to be freed even when user space never calls DONE.
However, it seems that the intended DONE routine will never give an
additional fput() of ths sock->file. The existing two of them are just
used to balance the reference added in sockfd_lookup().
This patch revert the mentioned commit to avoid the use-after-free. The
patched kernel could successfully pass the KUNIT test and boot to shell.
[ 0.733613] # Subtest: Handshake API tests
[ 0.734029] 1..11
[ 0.734255] KTAP version 1
[ 0.734542] # Subtest: req_alloc API fuzzing
[ 0.736104] ok 1 handshake_req_alloc NULL proto
[ 0.736114] ok 2 handshake_req_alloc CLASS_NONE
[ 0.736559] ok 3 handshake_req_alloc CLASS_MAX
[ 0.737020] ok 4 handshake_req_alloc no callbacks
[ 0.737488] ok 5 handshake_req_alloc no done callback
[ 0.737988] ok 6 handshake_req_alloc excessive privsize
[ 0.738529] ok 7 handshake_req_alloc all good
[ 0.739036] # req_alloc API fuzzing: pass:7 fail:0 skip:0 total:7
[ 0.739444] ok 1 req_alloc API fuzzing
[ 0.740065] ok 2 req_submit NULL req arg
[ 0.740436] ok 3 req_submit NULL sock arg
[ 0.740834] ok 4 req_submit NULL sock->file
[ 0.741236] ok 5 req_lookup works
[ 0.741621] ok 6 req_submit max pending
[ 0.741974] ok 7 req_submit multiple
[ 0.742382] ok 8 req_cancel before accept
[ 0.742764] ok 9 req_cancel after accept
[ 0.743151] ok 10 req_cancel after done
[ 0.743510] ok 11 req_destroy works
[ 0.743882] # Handshake API tests: pass:11 fail:0 skip:0 total:11
[ 0.744205] # Totals: pass:17 fail:0 skip:0 total:17
Acked-by: Chuck Lever <chuck.lever@oracle.com>
Fixes: 1ce77c998f ("net/handshake: Unpin sock->file if a handshake is cancelled")
Signed-off-by: Lin Ma <linma@zju.edu.cn>
Link: https://lore.kernel.org/r/20230613083204.633896-1-linma@zju.edu.cn
Link: https://lore.kernel.org/r/20230614015249.987448-1-linma@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
361b6889ae