7df9c24625
Dmitry has reported that a BUG_ON() condition in unix_notinflight()
may be triggered by a simple code that forwards unix socket in an
SCM_RIGHTS message.
That is caused by incorrect unix socket GC implementation in unix_gc().
The GC first collects list of candidates, then (a) decrements their
"children's" inflight counter, (b) checks which inflight counters are
now 0, and then (c) increments all inflight counters back.
(a) and (c) are done by calling scan_children() with inc_inflight or
dec_inflight as the second argument.
Commit 6209344f5a37 ("net: unix: fix inflight counting bug in garbage
collector") changed scan_children() such that it no longer considers
sockets that do not have UNIX_GC_CANDIDATE flag. It also added a block
of code that that unsets this flag _before_ invoking
scan_children(, dec_iflight, ). This may lead to incorrect inflight
counters for some sockets.
This change fixes this bug by changing order of operations:
UNIX_GC_CANDIDATE is now unset only after all inflight counters are
restored to the original state.
kernel BUG at net/unix/garbage.c:149!
RIP: 0010:[<ffffffff8717ebf4>] [<ffffffff8717ebf4>]
unix_notinflight+0x3b4/0x490 net/unix/garbage.c:149
Call Trace:
[<ffffffff8716cfbf>] unix_detach_fds.isra.19+0xff/0x170 net/unix/af_unix.c:1487
[<ffffffff8716f6a9>] unix_destruct_scm+0xf9/0x210 net/unix/af_unix.c:1496
[<ffffffff86a90a01>] skb_release_head_state+0x101/0x200 net/core/skbuff.c:655
[<ffffffff86a9808a>] skb_release_all+0x1a/0x60 net/core/skbuff.c:668
[<ffffffff86a980ea>] __kfree_skb+0x1a/0x30 net/core/skbuff.c:684
[<ffffffff86a98284>] kfree_skb+0x184/0x570 net/core/skbuff.c:705
[<ffffffff871789d5>] unix_release_sock+0x5b5/0xbd0 net/unix/af_unix.c:559
[<ffffffff87179039>] unix_release+0x49/0x90 net/unix/af_unix.c:836
[<ffffffff86a694b2>] sock_release+0x92/0x1f0 net/socket.c:570
[<ffffffff86a6962b>] sock_close+0x1b/0x20 net/socket.c:1017
[<ffffffff81a76b8e>] __fput+0x34e/0x910 fs/file_table.c:208
[<ffffffff81a771da>] ____fput+0x1a/0x20 fs/file_table.c:244
[<ffffffff81483ab0>] task_work_run+0x1a0/0x280 kernel/task_work.c:116
[< inline >] exit_task_work include/linux/task_work.h:21
[<ffffffff8141287a>] do_exit+0x183a/0x2640 kernel/exit.c:828
[<ffffffff8141383e>] do_group_exit+0x14e/0x420 kernel/exit.c:931
[<ffffffff814429d3>] get_signal+0x663/0x1880 kernel/signal.c:2307
[<ffffffff81239b45>] do_signal+0xc5/0x2190 arch/x86/kernel/signal.c:807
[<ffffffff8100666a>] exit_to_usermode_loop+0x1ea/0x2d0
arch/x86/entry/common.c:156
[< inline >] prepare_exit_to_usermode arch/x86/entry/common.c:190
[<ffffffff81009693>] syscall_return_slowpath+0x4d3/0x570
arch/x86/entry/common.c:259
[<ffffffff881478e6>] entry_SYSCALL_64_fastpath+0xc4/0xc6
Link: https://lkml.org/lkml/2017/3/6/252
Signed-off-by: Andrey Ulanov <andreyu@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Fixes: 6209344 ("net: unix: fix inflight counting bug in garbage collector")
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.