The patch below does not apply to the 4.15-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 0911287ce32b14fbc8aab0083151d9b54254091c Mon Sep 17 00:00:00 2001
From: Alexei Starovoitov ast@kernel.org Date: Fri, 2 Feb 2018 15:14:05 -0800 Subject: [PATCH] bpf: fix bpf_prog_array_copy_to_user() issues
1. move copy_to_user out of rcu section to fix the following issue:
./include/linux/rcupdate.h:302 Illegal context switch in RCU read-side critical section! stack backtrace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:53 lockdep_rcu_suspicious+0x123/0x170 kernel/locking/lockdep.c:4592 rcu_preempt_sleep_check include/linux/rcupdate.h:301 [inline] ___might_sleep+0x385/0x470 kernel/sched/core.c:6079 __might_sleep+0x95/0x190 kernel/sched/core.c:6067 __might_fault+0xab/0x1d0 mm/memory.c:4532 _copy_to_user+0x2c/0xc0 lib/usercopy.c:25 copy_to_user include/linux/uaccess.h:155 [inline] bpf_prog_array_copy_to_user+0x217/0x4d0 kernel/bpf/core.c:1587 bpf_prog_array_copy_info+0x17b/0x1c0 kernel/bpf/core.c:1685 perf_event_query_prog_array+0x196/0x280 kernel/trace/bpf_trace.c:877 _perf_ioctl kernel/events/core.c:4737 [inline] perf_ioctl+0x3e1/0x1480 kernel/events/core.c:4757
2. move *prog under rcu, since it's not ok to dereference it afterwards
3. in a rare case of prog array being swapped between bpf_prog_array_length() and bpf_prog_array_copy_to_user() calls make sure to copy zeros to user space, so the user doesn't walk over uninited prog_ids while kernel reported uattr->query.prog_cnt > 0
Reported-by: syzbot+7dbcd2d3b85f9b608b23@syzkaller.appspotmail.com Fixes: 468e2f64d220 ("bpf: introduce BPF_PROG_QUERY command") Signed-off-by: Alexei Starovoitov ast@kernel.org Signed-off-by: Daniel Borkmann daniel@iogearbox.net
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 5f35f93dcab2..29ca9208dcfa 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1576,25 +1576,41 @@ int bpf_prog_array_copy_to_user(struct bpf_prog_array __rcu *progs, __u32 __user *prog_ids, u32 cnt) { struct bpf_prog **prog; - u32 i = 0, id; - + unsigned long err = 0; + u32 i = 0, *ids; + bool nospc; + + /* users of this function are doing: + * cnt = bpf_prog_array_length(); + * if (cnt > 0) + * bpf_prog_array_copy_to_user(..., cnt); + * so below kcalloc doesn't need extra cnt > 0 check, but + * bpf_prog_array_length() releases rcu lock and + * prog array could have been swapped with empty or larger array, + * so always copy 'cnt' prog_ids to the user. + * In a rare race the user will see zero prog_ids + */ + ids = kcalloc(cnt, sizeof(u32), GFP_USER); + if (!ids) + return -ENOMEM; rcu_read_lock(); prog = rcu_dereference(progs)->progs; for (; *prog; prog++) { if (*prog == &dummy_bpf_prog.prog) continue; - id = (*prog)->aux->id; - if (copy_to_user(prog_ids + i, &id, sizeof(id))) { - rcu_read_unlock(); - return -EFAULT; - } + ids[i] = (*prog)->aux->id; if (++i == cnt) { prog++; break; } } + nospc = !!(*prog); rcu_read_unlock(); - if (*prog) + err = copy_to_user(prog_ids, ids, cnt * sizeof(u32)); + kfree(ids); + if (err) + return -EFAULT; + if (nospc) return -ENOSPC; return 0; }