diff options
author | Thomas Roessler <roessler@does-not-exist.org> | 1998-08-25 22:33:07 +0000 |
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committer | Thomas Roessler <roessler@does-not-exist.org> | 1998-08-25 22:33:07 +0000 |
commit | 986ab5e943db7aaed2aed98f8b74e4c26666fdd8 (patch) | |
tree | 58cfec1114686823dbdbf22cf2ca52f77eb1075d /dotlock.c | |
parent | 9044dd4d58af4b4d64a6e68b7b76c42d317e7ce5 (diff) |
CVS branch clean-up.
Diffstat (limited to 'dotlock.c')
-rw-r--r-- | dotlock.c | 714 |
1 files changed, 714 insertions, 0 deletions
diff --git a/dotlock.c b/dotlock.c new file mode 100644 index 00000000..0b978fdb --- /dev/null +++ b/dotlock.c @@ -0,0 +1,714 @@ +/* + * Copyright (C) 1996-8 Michael R. Elkins <me@cs.hmc.edu> + * Copyright (C) 1998 Thomas Roessler <roessler@guug.de> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; either version 2 of the License, or + * (at your option) any later version. + * + * This program is distributed in the hope that it will be useful, + * but WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the + * GNU General Public License for more details. + * + * You should have received a copy of the GNU General Public License + * along with this program; if not, write to the Free Software + * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. + */ + +/* + * This module either be compiled into Mutt, or it can be + * built as a separate program. For building it + * separately, define the DL_STANDALONE preprocessor + * macro. + */ + +#include <stdio.h> +#include <stdlib.h> +#include <string.h> + +#include <unistd.h> +#include <dirent.h> +#include <sys/file.h> +#include <sys/stat.h> +#include <sys/utsname.h> +#include <errno.h> +#include <time.h> +#include <fcntl.h> +#include <limits.h> + +#ifndef _POSIX_PATH_MAX +#include <posix1_lim.h> +#endif + +#include "dotlock.h" +#include "config.h" + +#ifdef DL_STANDALONE +#include "reldate.h" +#endif + +# define MAXLINKS 1024 /* maximum link depth */ + +# ifdef DL_STANDALONE + +# define LONG_STRING 1024 +# define MAXLOCKATTEMPT 5 + +# define strfcpy(A,B,C) strncpy(A,B,C), *(A+(C)-1)=0 + +# ifdef USE_SETGID + +# ifdef HAVE_SETEGID +# define SETEGID setegid +# else +# define SETEGID setgid +# endif +# ifndef S_ISLNK +# define S_ISLNK(x) (((x) & S_IFMT) == S_IFLNK ? 1 : 0) +# endif + +# endif + +# ifndef HAVE_SNPRINTF +extern int snprintf(char *, size_t, const char *, ...); +# endif + +#else /* DL_STANDALONE */ + +# ifdef USE_SETGID +# error Do not try to compile dotlock as a mutt module when requiring egid switching! +# endif + +# include "mutt.h" +# include "mx.h" + +#endif /* DL_STANDALONE */ + +static short f_try = 0; +static short f_force = 0; +static short f_unlock = 0; +static short f_priv = 0; +static int Retry = MAXLOCKATTEMPT; + +#ifdef DL_STANDALONE +static char *Hostname; +#endif + +#ifdef USE_SETGID +static gid_t UserGid; +static gid_t MailGid; +#endif + +static int dotlock_deference_symlink(char *, size_t, const char *); +static int dotlock_prepare(char *, size_t, const char *); + +#ifdef DL_STANDALONE +static int dotlock_init_privs(void); +static void usage(const char *); +#endif + +static void dotlock_expand_link(char *, const char *, const char *); +static void BEGIN_PRIVILEGED(void); +static void END_PRIVILEGED(void); + +/* These functions work on the current directory. + * Invoke dotlock_prepare() before and check their + * return value. + */ + +static int dotlock_try(void); +static int dotlock_unlock(const char *); +static int dotlock_lock(const char *); + + +#ifdef DL_STANDALONE + +int main(int argc, char **argv) +{ + int i; + char *p; + const char *f; + struct utsname utsname; + char realpath[_POSIX_PATH_MAX]; + + + /* first, drop privileges */ + + if(dotlock_init_privs() == -1) + return DL_EX_ERROR; + + + /* determine the system's host name */ + + uname(&utsname); + if(!(Hostname = strdup(utsname.nodename))) + return DL_EX_ERROR; + if((p = strchr(Hostname, '.'))) + *p = '\0'; + + + /* parse the command line options. */ + + while((i = getopt(argc, argv, "tfupr:")) != EOF) + { + switch(i) + { + case 't': f_try = 1; break; + case 'f': f_force = 1; break; + case 'u': f_unlock = 1; break; + case 'p': f_priv = 1; break; + case 'r': Retry = atoi(optarg); break; + default: usage(argv[0]); + } + } + + if(optind == argc || f_try + f_force + f_unlock > 1 || Retry < 0) + usage(argv[0]); + + f = argv[optind]; + + + /* If dotlock_prepare() succeeds [return value == 0], + * realpath contains the basename of f, and we have + * successfully changed our working directory to + * `dirname $f`. Additionally, f has been opened for + * reading to verify that the user has at least read + * permissions on that file. + * + * For a more detailed explanation of all this, see the + * lengthy comment below. + */ + + if(dotlock_prepare(realpath, sizeof(realpath), f) != 0) + return DL_EX_ERROR; + + /* Finally, actually perform the locking operation. */ + + if(f_try) + return dotlock_try(); + else if(f_unlock) + return dotlock_unlock(realpath); + else /* lock */ + return dotlock_lock(realpath); + +} + +/* + * Determine our effective group ID, and drop + * privileges. + * + * Return value: + * + * 0 - everything went fine + * -1 - we couldn't drop privileges. + * + */ + + +static int +dotlock_init_privs(void) +{ + +# ifdef USE_SETGID + + UserGid = getgid(); + MailGid = getegid(); + + if(SETEGID(UserGid) != 0) + return -1; + +# endif + + return 0; +} + + +#else /* DL_STANDALONE */ + +/* + * This function is intended to be invoked from within + * mutt instead of mx.c's invoke_dotlock(). + * + */ + +int dotlock_invoke(const char *path, int flags, int retry) +{ + int currdir; + int r; + char realpath[_POSIX_PATH_MAX]; + + if((currdir = open(".", O_RDONLY)) == -1) + return DL_EX_ERROR; + + if(!(flags & DL_FL_RETRY) || retry) + Retry = MAXLOCKATTEMPT; + else + Retry = 0; + + f_priv = f_try = f_unlock = f_force = 0; + + if(flags & DL_FL_FORCE) + f_force = 1; + + r = DL_EX_ERROR; + if(dotlock_prepare(realpath, sizeof(realpath), path) == -1) + goto bail; + + if(flags & DL_FL_TRY) + r = dotlock_try(); + else if(flags & DL_FL_UNLOCK) + r = dotlock_unlock(realpath); + else /* lock */ + r = dotlock_lock(realpath); + + bail: + + fchdir(currdir); + close(currdir); + + return r; +} + +#endif /* DL_STANDALONE */ + + +/* + * Get privileges + * + * This function re-acquires the privileges we may have + * if the user told us to do so by giving the "-p" + * command line option. + * + * BEGIN_PRIVILEGES() won't return if an error occurs. + * + */ + +static void +BEGIN_PRIVILEGED(void) +{ +#ifdef USE_SETGID + if(f_priv) + { + if(SETEGID(MailGid) != 0) + { + /* perror("setegid"); */ + exit(DL_EX_ERROR); + } + } +#endif +} + +/* + * Drop privileges + * + * This function drops the group privileges we may have. + * + * END_PRIVILEGED() won't return if an error occurs. + * + */ + +static void +END_PRIVILEGED(void) +{ +#ifdef USE_SETGID + if(f_priv) + { + if(SETEGID(UserGid) != 0) + { + /* perror("setegid"); */ + exit(DL_EX_ERROR); + } + } +#endif +} + +#ifdef DL_STANDALONE + +/* + * Usage information. + * + * This function doesn't return. + * + */ + +static void +usage(const char *av0) +{ + fprintf(stderr, "dotlock [Mutt %s (%s)]\n", VERSION, ReleaseDate); + fprintf(stderr, "usage: %s [-t|-f|-u] [-p] [-r <retries>] file\n", + av0); + + fputs("\noptions:" + "\n -t\t\ttry" + "\n -f\t\tforce" + "\n -u\t\tunlock" + "\n -p\t\tprivileged" +#ifndef USE_SETGID + " (ignored)" +#endif + "\n -r <retries>\tRetry locking" + "\n", stderr); + + exit(DL_EX_ERROR); +} + +#endif + +/* + * Access checking: Let's avoid to lock other users' mail + * spool files if we aren't permitted to read them. + * + * Some simple-minded access(2) checking isn't sufficient + * here: The problem is that the user may give us a + * deeply nested path to a file which has the same name + * as the file he wants to lock, but different + * permissions, say, e.g. + * /tmp/lots/of/subdirs/var/spool/mail/root. + * + * He may then try to replace /tmp/lots/of/subdirs by a + * symbolic link to / after we have invoked access() to + * check the file's permissions. The lockfile we'd + * create or remove would then actually be + * /var/spool/mail/root. + * + * To avoid this attack, we proceed as follows: + * + * - First, follow symbolic links a la + * dotlock_deference_symlink(). + * + * - get the result's dirname. + * + * - chdir to this directory. If you can't, bail out. + * + * - try to open the file in question, only using its + * basename. If you can't, bail out. + * + * - fstat that file and compare the result to a + * subsequent lstat (only using the basename). If + * the comparison fails, bail out. + * + * dotlock_prepare() is invoked from main() directly + * after the command line parsing has been done. + * + * Return values: + * + * 0 - Evereything's fine. The program's new current + * directory is the contains the file to be locked. + * The string pointed to by bn contains the name of + * the file to be locked. + * + * -1 - Something failed. Don't continue. + * + * tlr, Jul 15 1998 + */ + +static int +dotlock_prepare(char *bn, size_t l, const char *f) +{ + struct stat fsb, lsb; + char realpath[_POSIX_PATH_MAX]; + char *basename, *dirname; + char *p; + int fd; + int r; + + if(dotlock_deference_symlink(realpath, sizeof(realpath), f) == -1) + return -1; + + if((p = strrchr(realpath, '/'))) + { + *p = '\0'; + basename = p + 1; + dirname = realpath; + } + else + { + basename = realpath; + dirname = "."; + } + + if(strlen(basename) + 1 > l) + return -1; + + strfcpy(bn, basename, l); + + if(chdir(dirname) == -1) + return -1; + + if((fd = open(basename, O_RDONLY)) == -1) + return -1; + + r = fstat(fd, &fsb); + close(fd); + + if(r == -1) + return -1; + + if(lstat(basename, &lsb) == -1) + return -1; + + if(S_ISLNK(lsb.st_mode)) + return -1; + + if((lsb.st_dev != fsb.st_dev) || + (lsb.st_ino != fsb.st_ino) || + (lsb.st_mode != fsb.st_mode) || + (lsb.st_nlink != fsb.st_nlink) || + (lsb.st_uid != fsb.st_uid) || + (lsb.st_gid != fsb.st_gid) || + (lsb.st_rdev != fsb.st_rdev) || + (lsb.st_size != fsb.st_size)) + { + /* something's fishy */ + return -1; + } + + return 0; +} + +/* + * Expand a symbolic link. + * + * This function expects newpath to have space for + * at least _POSIX_PATH_MAX characters. + * + */ + +static void +dotlock_expand_link (char *newpath, const char *path, const char *link) +{ + const char *lb = NULL; + size_t len; + + /* link is full path */ + if (*link == '/') + { + strfcpy (newpath, link, _POSIX_PATH_MAX); + return; + } + + if ((lb = strrchr (path, '/')) == NULL) + { + /* no path in link */ + strfcpy (newpath, link, _POSIX_PATH_MAX); + return; + } + + len = lb - path + 1; + memcpy (newpath, path, len); + strfcpy (newpath + len, link, _POSIX_PATH_MAX - len); +} + + +/* + * Deference a chain of symbolic links + * + * The final path is written to d. + * + */ + +static int +dotlock_deference_symlink(char *d, size_t l, const char *path) +{ + struct stat sb; + char realpath[_POSIX_PATH_MAX]; + const char *pathptr = path; + int count = 0; + + while(count++ < MAXLINKS) + { + if(lstat(pathptr, &sb) == -1) + { + /* perror(pathptr); */ + return -1; + } + + if(S_ISLNK (sb.st_mode)) + { + char linkfile[_POSIX_PATH_MAX]; + char linkpath[_POSIX_PATH_MAX]; + int len; + + if((len = readlink(pathptr, linkfile, sizeof(linkfile))) == -1) + { + /* perror(pathptr); */ + return -1; + } + + linkfile[len] = '\0'; + dotlock_expand_link(linkpath, pathptr, linkfile); + strfcpy(realpath, linkpath, sizeof(realpath)); + pathptr = realpath; + } + else + break; + } + + strfcpy(d, pathptr, l); + return 0; +} + +/* + * Dotlock a file. + * + * realpath is assumed _not_ to be an absolute path to + * the file we are about to lock. Invoke + * dotlock_prepare() before using this function! + * + */ + +static int +dotlock_lock(const char *realpath) +{ + char lockfile[_POSIX_PATH_MAX + LONG_STRING]; + char nfslockfile[_POSIX_PATH_MAX + LONG_STRING]; + size_t prev_size = 0; + int fd; + int count = 0; + struct stat sb; + time_t t; + + snprintf(nfslockfile, sizeof(nfslockfile), "%s.%s.%d", + realpath, Hostname, (int) getpid()); + snprintf(lockfile, sizeof(lockfile), "%s.lock", realpath); + + + BEGIN_PRIVILEGED(); + + unlink(nfslockfile); + + while ((fd = open (nfslockfile, O_WRONLY | O_EXCL | O_CREAT, 0)) < 0) + { + END_PRIVILEGED(); + + + if (errno != EAGAIN) + { + /* perror ("cannot open NFS lock file"); */ + return DL_EX_ERROR; + } + + + BEGIN_PRIVILEGED(); + } + + END_PRIVILEGED(); + + + close(fd); + + while(1) + { + + BEGIN_PRIVILEGED(); + link(nfslockfile, lockfile); + END_PRIVILEGED(); + + if(stat(nfslockfile, &sb) != 0) + { + /* perror("stat"); */ + return DL_EX_ERROR; + } + + if(sb.st_nlink == 2) + break; + + if(count == 0) + prev_size = sb.st_size; + + if(prev_size == sb.st_size && ++count > Retry) + { + if(f_force) + { + BEGIN_PRIVILEGED(); + unlink(lockfile); + END_PRIVILEGED(); + + count = 0; + continue; + } + else + { + BEGIN_PRIVILEGED(); + unlink(nfslockfile); + END_PRIVILEGED(); + return DL_EX_EXIST; + } + } + + prev_size = sb.st_size; + + /* don't trust sleep(3) as it may be interrupted + * by users sending signals. + */ + + t = time(NULL); + do { + sleep(1); + } while (time(NULL) == t); + } + + BEGIN_PRIVILEGED(); + unlink(nfslockfile); + END_PRIVILEGED(); + + return DL_EX_OK; +} + + +/* + * Unlock a file. + * + * The same comment as for dotlock_lock() applies here. + * + */ + +static int +dotlock_unlock(const char *realpath) +{ + char lockfile[_POSIX_PATH_MAX + LONG_STRING]; + int i; + + snprintf(lockfile, sizeof(lockfile), "%s.lock", + realpath); + + BEGIN_PRIVILEGED(); + i = unlink(lockfile); + END_PRIVILEGED(); + + if(i == -1) + return DL_EX_ERROR; + + return DL_EX_OK; +} + + +/* + * Check if a file can be locked at all. + * + * The same comment as for dotlock_lock() applies here. + * + */ + +static int +dotlock_try(void) +{ +#ifdef USE_SETGID + struct stat sb; +#endif + + if(access(".", W_OK) == 0) + return DL_EX_OK; + +#ifdef USE_SETGID + if(stat(".", &sb) == 0) + { + if((sb.st_mode & S_IWGRP) == S_IWGRP && sb.st_gid == MailGid) + return DL_EX_NEED_PRIVS; + } +#endif + + return DL_EX_IMPOSSIBLE; +} |