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// Needed for O_DIRECTORY, must be defined before fcntl.h is included
9// (and it can be included earlier than the explicit #include below
10// in some versions of glibc).
11#define _GNU_SOURCE
12
13#include "sandbox/linux/suid/process_util.h"
14
15#include <fcntl.h>
16#include <inttypes.h>
17#include <limits.h>
18#include <stdio.h>
19#include <stdlib.h>
20#include <string.h>
21#include <sys/stat.h>
22#include <sys/types.h>
23#include <unistd.h>
24
25// Ranges for the current (oom_score_adj) and previous (oom_adj)
26// flavors of OOM score.
27static const int kMaxOomScore = 1000;
28static const int kMaxOldOomScore = 15;
29
30// NOTE: This is not the only version of this function in the source:
31// the base library (in process_util_linux.cc) also has its own C++ version.
32bool AdjustOOMScore(pid_t process, int score) {
33  if (score < 0 || score > kMaxOomScore)
34    return false;
35
36  char oom_adj[27];  // "/proc/" + log_10(2**64) + "\0"
37                     //    6     +       20     +     1         = 27
38  snprintf(oom_adj, sizeof(oom_adj), "/proc/%" PRIdMAX, (intmax_t)process);
39
40  const int dirfd = open(oom_adj, O_RDONLY | O_DIRECTORY);
41  if (dirfd < 0)
42    return false;
43
44  struct stat statbuf;
45  if (fstat(dirfd, &statbuf) < 0) {
46    close(dirfd);
47    return false;
48  }
49  if (getuid() != statbuf.st_uid) {
50    close(dirfd);
51    return false;
52  }
53
54  int fd = openat(dirfd, "oom_score_adj", O_WRONLY);
55  if (fd < 0) {
56    // We failed to open oom_score_adj, so let's try for the older
57    // oom_adj file instead.
58    fd = openat(dirfd, "oom_adj", O_WRONLY);
59    if (fd < 0) {
60      // Nope, that doesn't work either.
61      return false;
62    } else {
63      // If we're using the old oom_adj file, the allowed range is now
64      // [0, kMaxOldOomScore], so we scale the score.  This may result in some
65      // aliasing of values, of course.
66      score = score * kMaxOldOomScore / kMaxOomScore;
67    }
68  }
69  close(dirfd);
70
71  char buf[11];  // 0 <= |score| <= kMaxOomScore; using log_10(2**32) + 1 size
72  snprintf(buf, sizeof(buf), "%d", score);
73  size_t len = strlen(buf);
74
75  ssize_t bytes_written = write(fd, buf, len);
76  close(fd);
77  return (bytes_written == (ssize_t)len);
78}
79