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      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 <stddef.h>
     19 #include <stdio.h>
     20 #include <stdlib.h>
     21 #include <string.h>
     22 #include <sys/stat.h>
     23 #include <sys/types.h>
     24 #include <unistd.h>
     25 
     26 // Ranges for the current (oom_score_adj) and previous (oom_adj)
     27 // flavors of OOM score.
     28 static const int kMaxOomScore = 1000;
     29 static const int kMaxOldOomScore = 15;
     30 
     31 // NOTE: This is not the only version of this function in the source:
     32 // the base library (in process_util_linux.cc) also has its own C++ version.
     33 bool AdjustOOMScore(pid_t process, int score) {
     34   if (score < 0 || score > kMaxOomScore)
     35     return false;
     36 
     37   char oom_adj[27];  // "/proc/" + log_10(2**64) + "\0"
     38                      //    6     +       20     +     1         = 27
     39   snprintf(oom_adj, sizeof(oom_adj), "/proc/%" PRIdMAX, (intmax_t)process);
     40 
     41   const int dirfd = open(oom_adj, O_RDONLY | O_DIRECTORY);
     42   if (dirfd < 0)
     43     return false;
     44 
     45   struct stat statbuf;
     46   if (fstat(dirfd, &statbuf) < 0) {
     47     close(dirfd);
     48     return false;
     49   }
     50   if (getuid() != statbuf.st_uid) {
     51     close(dirfd);
     52     return false;
     53   }
     54 
     55   int fd = openat(dirfd, "oom_score_adj", O_WRONLY);
     56   if (fd < 0) {
     57     // We failed to open oom_score_adj, so let's try for the older
     58     // oom_adj file instead.
     59     fd = openat(dirfd, "oom_adj", O_WRONLY);
     60     if (fd < 0) {
     61       // Nope, that doesn't work either.
     62       return false;
     63     } else {
     64       // If we're using the old oom_adj file, the allowed range is now
     65       // [0, kMaxOldOomScore], so we scale the score.  This may result in some
     66       // aliasing of values, of course.
     67       score = score * kMaxOldOomScore / kMaxOomScore;
     68     }
     69   }
     70   close(dirfd);
     71 
     72   char buf[11];  // 0 <= |score| <= kMaxOomScore; using log_10(2**32) + 1 size
     73   snprintf(buf, sizeof(buf), "%d", score);
     74   size_t len = strlen(buf);
     75 
     76   ssize_t bytes_written = write(fd, buf, len);
     77   close(fd);
     78   return (bytes_written == (ssize_t)len);
     79 }
     80