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