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When kcm is loaded while many processes try to create a KCM socket, a
crash occurs:
BUG: unable to handle kernel NULL pointer dereference at 000000000000000e
IP: mutex_lock+0x27/0x40 kernel/locking/mutex.c:240
PGD 8000000016ef2067 P4D 8000000016ef2067 PUD 3d6e9067 PMD 0
Oops: 0002 [#1] SMP KASAN PTI
CPU: 0 PID: 7005 Comm: syz-executor.5 Not tainted 4.12.14-396-default #1 SLE15-SP1 (unreleased)
RIP: 0010:mutex_lock+0x27/0x40 kernel/locking/mutex.c:240
RSP: 0018:ffff88000d487a00 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 000000000000000e RCX: 1ffff100082b0719
...
CR2: 000000000000000e CR3: 000000004b1bc003 CR4: 0000000000060ef0
Call Trace:
kcm_create+0x600/0xbf0 [kcm]
__sock_create+0x324/0x750 net/socket.c:1272
...
This is due to race between sock_create and unfinished
register_pernet_device. kcm_create tries to do "net_generic(net,
kcm_net_id)". but kcm_net_id is not initialized yet.
So switch the order of the two to close the race.
This can be reproduced with mutiple processes doing socket(PF_KCM, ...)
and one process doing module removal.
Fixes: ab7ac4eb98 ("kcm: Kernel Connection Multiplexor module")
Reviewed-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
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https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
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.