sandbox/linux/suid/process_util_linux.c

   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.
  27 static const int kMaxOomScore = 1000;
  28 static 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.
  32 bool 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 }