1// Copyright (c) 2012 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// The following is the C version of code from base/process_utils_linux.cc.
6// We shouldn't link against C++ code in a setuid binary.
7
8#define _GNU_SOURCE  // needed for O_DIRECTORY
9
10#include "process_util.h"
11
12#include <fcntl.h>
13#include <inttypes.h>
14#include <limits.h>
15#include <stdio.h>
16#include <stdlib.h>
17#include <string.h>
18#include <sys/stat.h>
19#include <sys/types.h>
20#include <unistd.h>
21
22// Ranges for the current (oom_score_adj) and previous (oom_adj)
23// flavors of OOM score.
24static const int kMaxOomScore = 1000;
25static const int kMaxOldOomScore = 15;
26
27// NOTE: This is not the only version of this function in the source:
28// the base library (in process_util_linux.cc) also has its own C++ version.
29bool AdjustOOMScore(pid_t process, int score) {
30  if (score < 0 || score > kMaxOomScore)
31    return false;
32
33  char oom_adj[27];  // "/proc/" + log_10(2**64) + "\0"
34                     //    6     +       20     +     1         = 27
35  snprintf(oom_adj, sizeof(oom_adj), "/proc/%" PRIdMAX, (intmax_t)process);
36
37  const int dirfd = open(oom_adj, O_RDONLY | O_DIRECTORY);
38  if (dirfd < 0)
39    return false;
40
41  struct stat statbuf;
42  if (fstat(dirfd, &statbuf) < 0) {
43    close(dirfd);
44    return false;
45  }
46  if (getuid() != statbuf.st_uid) {
47    close(dirfd);
48    return false;
49  }
50
51  int fd = openat(dirfd, "oom_score_adj", O_WRONLY);
52  if (fd < 0) {
53    // We failed to open oom_score_adj, so let's try for the older
54    // oom_adj file instead.
55    fd = openat(dirfd, "oom_adj", O_WRONLY);
56    if (fd < 0) {
57      // Nope, that doesn't work either.
58      return false;
59    } else {
60      // If we're using the old oom_adj file, the allowed range is now
61      // [0, kMaxOldOomScore], so we scale the score.  This may result in some
62      // aliasing of values, of course.
63      score = score * kMaxOldOomScore / kMaxOomScore;
64    }
65  }
66  close(dirfd);
67
68  char buf[11];  // 0 <= |score| <= kMaxOomScore; using log_10(2**32) + 1 size
69  snprintf(buf, sizeof(buf), "%d", score);
70  size_t len = strlen(buf);
71
72  ssize_t bytes_written = write(fd, buf, len);
73  close(fd);
74  return (bytes_written == len);
75}
76