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tools/bpftool: fix a percpu_array map dump problem

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I hit the following problem when I tried to use bpftool
to dump a percpu array.

  $ sudo ./bpftool map show
  61: percpu_array  name stub  flags 0x0
          key 4B  value 4B  max_entries 1  memlock 4096B
  ...
  $ sudo ./bpftool map dump id 61
  bpftool: malloc.c:2406: sysmalloc: Assertion
  `(old_top == initial_top (av) && old_size == 0) || \
   ((unsigned long) (old_size) >= MINSIZE && \
   prev_inuse (old_top) && \
   ((unsigned long) old_end & (pagesize - 1)) == 0)'
  failed.
  Aborted

Further debugging revealed that this is due to
miscommunication between bpftool and kernel.
For example, for the above percpu_array with value size of 4B.
The map info returned to user space has value size of 4B.

In bpftool, the values array for lookup is allocated like:
   info->value_size * get_possible_cpus() = 4 * get_possible_cpus()
In kernel (kernel/bpf/syscall.c), the values array size is
rounded up to multiple of 8.
   round_up(map->value_size, 8) * num_possible_cpus()
   = 8 * num_possible_cpus()
So when kernel copies the values to user buffer, the kernel will
overwrite beyond user buffer boundary.

This patch fixed the issue by allocating and stepping through
percpu map value array properly in bpftool.

Fixes: 71bb428fe2 ("tools: bpf: add bpftool")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
This commit is contained in:
Yonghong Song 2018-07-30 08:49:03 -07:00 committed by Daniel Borkmann
parent 61f4b23769
commit 573b3aa694
1 changed files with 9 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

14
tools/bpf/bpftool/map.c
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@ -36,6 +36,7 @@
#include <assert.h>
#include <errno.h>
#include <fcntl.h>
#include <linux/kernel.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
@ -90,7 +91,8 @@ static bool map_is_map_of_progs(__u32 type)
static void *alloc_value(struct bpf_map_info *info)
{
if (map_is_per_cpu(info->type))
return malloc(info->value_size * get_possible_cpus());
return malloc(round_up(info->value_size, 8) *
get_possible_cpus());
else
return malloc(info->value_size);
}
@ -161,9 +163,10 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key,
jsonw_name(json_wtr, "value");
print_hex_data_json(value, info->value_size);
} else {
unsigned int i, n;
unsigned int i, n, step;
n = get_possible_cpus();
step = round_up(info->value_size, 8);
jsonw_name(json_wtr, "key");
print_hex_data_json(key, info->key_size);
@ -176,7 +179,7 @@ static void print_entry_json(struct bpf_map_info *info, unsigned char *key,
jsonw_int_field(json_wtr, "cpu", i);
jsonw_name(json_wtr, "value");
print_hex_data_json(value + i * info->value_size,
print_hex_data_json(value + i * step,
info->value_size);
jsonw_end_object(json_wtr);
@ -207,9 +210,10 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
printf("\n");
} else {
unsigned int i, n;
unsigned int i, n, step;
n = get_possible_cpus();
step = round_up(info->value_size, 8);
printf("key:\n");
fprint_hex(stdout, key, info->key_size, " ");
@ -217,7 +221,7 @@ static void print_entry_plain(struct bpf_map_info *info, unsigned char *key,
for (i = 0; i < n; i++) {
printf("value (CPU %02d):%c",
i, info->value_size > 16 ? '\n' : ' ');
fprint_hex(stdout, value + i * info->value_size,
fprint_hex(stdout, value + i * step,
info->value_size, " ");
printf("\n");
}