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Yonghong Song e1a75e94a3 bpf: Fix a rcu warning for bpffs map pretty-print 
[ Upstream commit ce880cb825fcc22d4e39046a6c3a3a7f6603883d ]

Running selftest
  ./btf_btf -p
the kernel had the following warning:
  [   51.528185] WARNING: CPU: 3 PID: 1756 at kernel/bpf/hashtab.c:717 htab_map_get_next_key+0x2eb/0x300
  [   51.529217] Modules linked in:
  [   51.529583] CPU: 3 PID: 1756 Comm: test_btf Not tainted 5.9.0-rc1+ #878
  [   51.530346] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-1.el7.centos 04/01/2014
  [   51.531410] RIP: 0010:htab_map_get_next_key+0x2eb/0x300
  ...
  [   51.542826] Call Trace:
  [   51.543119]  map_seq_next+0x53/0x80
  [   51.543528]  seq_read+0x263/0x400
  [   51.543932]  vfs_read+0xad/0x1c0
  [   51.544311]  ksys_read+0x5f/0xe0
  [   51.544689]  do_syscall_64+0x33/0x40
  [   51.545116]  entry_SYSCALL_64_after_hwframe+0x44/0xa9

The related source code in kernel/bpf/hashtab.c:
  709 static int htab_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
  710 {
  711         struct bpf_htab *htab = container_of(map, struct bpf_htab, map);
  712         struct hlist_nulls_head *head;
  713         struct htab_elem *l, *next_l;
  714         u32 hash, key_size;
  715         int i = 0;
  716
  717         WARN_ON_ONCE(!rcu_read_lock_held());

In kernel/bpf/inode.c, bpffs map pretty print calls map->ops->map_get_next_key()
without holding a rcu_read_lock(), hence causing the above warning.
To fix the issue, just surrounding map->ops->map_get_next_key() with rcu read lock.

Fixes: a26ca7c982 ("bpf: btf: Add pretty print support to the basic arraymap")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200916004401.146277-1-yhs@fb.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
2020-10-01 13:14:52 +02:00
..
arraymap.c bpf: decouple btf from seq bpf fs dump and enable more maps 2018-08-13 00:52:45 +02:00
bpf_lru_list.c bpf: lru: Lower the PERCPU_NR_SCANS from 16 to 4 2017-04-17 13:55:52 -04:00
bpf_lru_list.h bpf: Only set node->ref = 1 if it has not been set 2017-09-01 09:57:39 -07:00
btf.c bpf: Explicitly memset some bpf info structures declared on the stack 2020-04-02 15:28:23 +02:00
cgroup.c bpf: introduce update_effective_progs() 2018-08-07 14:29:55 +02:00
core.c bpf: fix bpf_jit_limit knob for PAGE_SIZE >= 64K 2019-07-10 09:53:47 +02:00
cpumap.c cpumap: Avoid warning when CONFIG_DEBUG_PER_CPU_MAPS is enabled 2020-05-02 17:25:53 +02:00
devmap.c bpf: devmap: fix wrong interface selection in notifier_call 2019-12-01 09:17:01 +01:00
disasm.c bpf: Remove struct bpf_verifier_env argument from print_bpf_insn 2018-03-23 17:38:57 +01:00
disasm.h bpf: Remove struct bpf_verifier_env argument from print_bpf_insn 2018-03-23 17:38:57 +01:00
hashtab.c bpf: Remove recursion prevention from rcu free callback 2020-10-01 13:14:34 +02:00
helpers.c bpf: introduce the bpf_get_local_storage() helper function 2018-08-03 00:47:32 +02:00
inode.c bpf: Fix a rcu warning for bpffs map pretty-print 2020-10-01 13:14:52 +02:00
local_storage.c bpf: allocate local storage buffers using GFP_ATOMIC 2018-12-17 09:24:33 +01:00
lpm_trie.c bpf: lpm_trie: check left child of last leftmost node for NULL 2019-07-03 13:14:48 +02:00
Makefile bpf: silence warning messages in core 2019-07-26 09:14:06 +02:00
map_in_map.c bpf: fix inner map masking to prevent oob under speculation 2019-01-31 08:14:41 +01:00
map_in_map.h bpf: Add syscall lookup support for fd array and htab 2017-06-29 13:13:25 -04:00
offload.c bpf, offload: Replace bitwise AND by logical AND in bpf_prog_offload_info_fill 2020-02-28 16:38:59 +01:00
percpu_freelist.c bpf: fix lockdep false positive in percpu_freelist 2019-03-13 14:02:36 -07:00
percpu_freelist.h bpf: fix lockdep false positive in percpu_freelist 2019-03-13 14:02:36 -07:00
reuseport_array.c bpf: Introduce BPF_MAP_TYPE_REUSEPORT_SOCKARRAY 2018-08-11 01:58:46 +02:00
sockmap.c bpf: sockmap, fix transition through disconnect without close 2018-09-22 02:46:41 +02:00
stackmap.c bpf/stackmap: Fix deadlock with rq_lock in bpf_get_stack() 2019-12-31 16:35:20 +01:00
syscall.c bpf: Check correct cred for CAP_SYSLOG in bpf_dump_raw_ok() 2020-07-16 08:17:27 +02:00
tnum.c bpf: Fix incorrect verifier simulation of ARSH under ALU32 2020-01-23 08:21:32 +01:00
verifier.c bpf: fix buggy r0 retval refinement for tracing helpers 2020-04-23 10:30:24 +02:00
xskmap.c xsk: do not call synchronize_net() under RCU read lock 2018-10-11 10:19:01 +02:00