linux-kernel - [PATCH net 2/3] bpf: fix splat for illegal devmap percpu allocation

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Date:   Tue, 17 Oct 2017 16:55:53 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     davem@...emloft.net
Cc:     tj@...nel.org, ast@...nel.org, john.fastabend@...il.com,
        mark.rutland@....com, richard@....at, sp3485@...umbia.edu,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>
Subject: [PATCH net 2/3] bpf: fix splat for illegal devmap percpu allocation

It was reported that syzkaller was able to trigger a splat on
devmap percpu allocation due to illegal/unsupported allocation
request size passed to __alloc_percpu():

  [   70.094249] illegal size (32776) or align (8) for percpu allocation
  [   70.094256] ------------[ cut here ]------------
  [   70.094259] WARNING: CPU: 3 PID: 3451 at mm/percpu.c:1365 pcpu_alloc+0x96/0x630
  [...]
  [   70.094325] Call Trace:
  [   70.094328]  __alloc_percpu_gfp+0x12/0x20
  [   70.094330]  dev_map_alloc+0x134/0x1e0
  [   70.094331]  SyS_bpf+0x9bc/0x1610
  [   70.094333]  ? selinux_task_setrlimit+0x5a/0x60
  [   70.094334]  ? security_task_setrlimit+0x43/0x60
  [   70.094336]  entry_SYSCALL_64_fastpath+0x1a/0xa5

This was due to too large max_entries for the map such that we
surpassed the upper limit of PCPU_MIN_UNIT_SIZE. It's fine to
fail naturally here, so switch to __alloc_percpu_gfp() and pass
__GFP_NOWARN instead.

Fixes: 11393cc9b9be ("xdp: Add batching support to redirect map")
Reported-by: Mark Rutland <mark.rutland@....com>
Reported-by: Shankara Pailoor <sp3485@...umbia.edu>
Reported-by: Richard Weinberger <richard@....at>
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Cc: John Fastabend <john.fastabend@...il.com>
---
 kernel/bpf/devmap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index e093d9a..920428d 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -111,8 +111,9 @@ static struct bpf_map *dev_map_alloc(union bpf_attr *attr)
 	err = -ENOMEM;
 
 	/* A per cpu bitfield with a bit per possible net device */
-	dtab->flush_needed = __alloc_percpu(dev_map_bitmap_size(attr),
-					    __alignof__(unsigned long));
+	dtab->flush_needed = __alloc_percpu_gfp(dev_map_bitmap_size(attr),
+						__alignof__(unsigned long),
+						GFP_KERNEL | __GFP_NOWARN);
 	if (!dtab->flush_needed)
 		goto free_dtab;
 
-- 
1.9.3