Taehee Yoo 84258438e8 net: bpfilter: use get_pid_task instead of pid_task ... pid_task() dereferences rcu protected tasks array. But there is no rcu_read_lock() in shutdown_umh() routine so that rcu_read_lock() is needed. get_pid_task() is wrapper function of pid_task. it holds rcu_read_lock() then calls pid_task(). if task isn't NULL, it increases reference count of task. test commands: %modprobe bpfilter %modprobe -rv bpfilter splat looks like: [15102.030932] ============================= [15102.030957] WARNING: suspicious RCU usage [15102.030985] 4.19.0-rc7+ #21 Not tainted [15102.031010] ----------------------------- [15102.031038] kernel/pid.c:330 suspicious rcu_dereference_check() usage! [15102.031063] other info that might help us debug this: [15102.031332] rcu_scheduler_active = 2, debug_locks = 1 [15102.031363] 1 lock held by modprobe/1570: [15102.031389] #0: 00000000580ef2b0 (bpfilter_lock){+.+.}, at: stop_umh+0x13/0x52 [bpfilter] [15102.031552] stack backtrace: [15102.031583] CPU: 1 PID: 1570 Comm: modprobe Not tainted 4.19.0-rc7+ #21 [15102.031607] Hardware name: To be filled by O.E.M. To be filled by O.E.M./Aptio CRB, BIOS 5.6.5 07/08/2015 [15102.031628] Call Trace: [15102.031676] dump_stack+0xc9/0x16b [15102.031723] ? show_regs_print_info+0x5/0x5 [15102.031801] ? lockdep_rcu_suspicious+0x117/0x160 [15102.031855] pid_task+0x134/0x160 [15102.031900] ? find_vpid+0xf0/0xf0 [15102.032017] shutdown_umh.constprop.1+0x1e/0x53 [bpfilter] [15102.032055] stop_umh+0x46/0x52 [bpfilter] [15102.032092] __x64_sys_delete_module+0x47e/0x570 [ ... ] Fixes: d2ba09c17a ("net: add skeleton of bpfilter kernel module") Signed-off-by: Taehee Yoo <ap420073@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>		2018-10-17 22:03:40 -07:00
..
.gitignore	bpfilter: ignore binary files	2018-06-20 09:07:46 +09:00
bpfilter_kern.c	net: bpfilter: use get_pid_task instead of pid_task	2018-10-17 22:03:40 -07:00
bpfilter_umh_blob.S	bpfilter: include bpfilter_umh in assembly instead of using objcopy	2018-06-28 21:39:16 +09:00
Kconfig	bpfilter: remove trailing newline	2018-07-24 14:10:42 -07:00
main.c	bpfilter: don't pass O_CREAT when opening console for debug	2018-05-24 09:36:49 -04:00
Makefile	kbuild: Rename HOSTLDFLAGS to KBUILD_HOSTLDFLAGS	2018-07-18 01:18:05 +09:00
msgfmt.h