--- systemvp should pretty much be a drop-in replacement for system with the exception that it takes an argv array and uses exec. If anybody wants to play with it to stress test it a little, I have a self-contained copy and test program at: https://github.com/andrewgregory/snippets/blob/systemv/c/systemv.c TODO: * update docs * fix debug logging * should the command be run with PATH lookup (execv vs execvp)? * Is the use of mmap with MAP_ANONYMOUS okay? MAP_ANONYMOUS is not POSIX but "most systems also support MAP_ANONYMOUS (or its synonym MAP_ANON)" (mmap(2)). * should we reset signals prior to exec'ing like we do with hooks/scripts? src/pacman/conf.c | 95 ++++++++++++++++++++++++++++++++++++++--------- src/pacman/conf.h | 2 + 2 files changed, 80 insertions(+), 17 deletions(-) diff --git a/src/pacman/conf.c b/src/pacman/conf.c index 2d8518c4..faf446dc 100644 --- a/src/pacman/conf.c +++ b/src/pacman/conf.c @@ -26,9 +26,11 @@ #include #include #include /* strdup */ +#include #include #include #include /* uname */ +#include #include /* pacman */ @@ -153,6 +155,7 @@ int config_free(config_t *oldconfig) free(oldconfig->print_format); free(oldconfig->arch); free(oldconfig); + _alpm_wordsplit_free(oldconfig->xfercommand_argv); return 0; } @@ -201,18 +204,59 @@ static char *get_tempfile(const char *path, const char *filename) return tempfile; } +static int systemvp(const char *file, char *const argv[]) +{ + int pid, *err; + + err = mmap(NULL, sizeof(*err), PROT_READ | PROT_WRITE, + MAP_SHARED | MAP_ANONYMOUS, -1, 0); + if(err == NULL) { + return -1; + } + + pid = fork(); + if(pid == -1) { + /* error */ + munmap(err, sizeof(*err)); + return -1; + } else if(pid == 0) { + /* child */ + *err = 0; + execvp(file, argv); + *err = errno; + munmap(err, sizeof(*err)); + _Exit(1); + } else { + /* parent */ + int status; + while(waitpid(pid, &status, 0) == -1) { + if(errno != EINTR) { + munmap(err, sizeof(*err)); + return -1; + } + } + if(*err != 0) { + errno = *err; + status = -1; + } + munmap(err, sizeof(*err)); + return status; + } +} + /** External fetch callback */ static int download_with_xfercommand(const char *url, const char *localpath, int force) { int ret = 0, retval; int usepart = 0; - int cwdfd; + int cwdfd = -1; struct stat st; - char *parsedcmd, *tempcmd; char *destfile, *tempfile, *filename; + const char **argv; + size_t i; - if(!config->xfercommand) { + if(!config->xfercommand_argv) { return -1; } @@ -230,17 +274,20 @@ static int download_with_xfercommand(const char *url, const char *localpath, unlink(destfile); } - tempcmd = strdup(config->xfercommand); - /* replace all occurrences of %o with fn.part */ - if(strstr(tempcmd, "%o")) { - usepart = 1; - parsedcmd = strreplace(tempcmd, "%o", tempfile); - free(tempcmd); - tempcmd = parsedcmd; + if((argv = calloc(config->xfercommand_argc + 1, sizeof(char*))) == NULL) { + pm_printf(ALPM_LOG_ERROR, _("could not get current working directory\n")); + goto cleanup; + } + + for(i = 0; i <= config->xfercommand_argc; i++) { + const char *val = config->xfercommand_argv[i]; + if(val && strcmp(val, "%o") == 0) { + val = tempfile; + } else if(val && strcmp(val, "%u") == 0) { + val = url; + } + argv[i] = val; } - /* replace all occurrences of %u with the download URL */ - parsedcmd = strreplace(tempcmd, "%u", url); - free(tempcmd); /* save the cwd so we can restore it later */ do { @@ -256,9 +303,13 @@ static int download_with_xfercommand(const char *url, const char *localpath, ret = -1; goto cleanup; } - /* execute the parsed command via /bin/sh -c */ - pm_printf(ALPM_LOG_DEBUG, "running command: %s\n", parsedcmd); - retval = system(parsedcmd); + + printf("running command: %s", config->xfercommand_argv[0]); + for(i = 1; argv[i]; i++) { + printf(" '%s'", argv[i]); + } + printf("\n"); + retval = systemvp(argv[0], (char**)argv); if(retval == -1) { pm_printf(ALPM_LOG_WARNING, _("running XferCommand: fork failed!\n")); @@ -296,7 +347,6 @@ cleanup: } free(destfile); free(tempfile); - free(parsedcmd); return ret; } @@ -544,6 +594,17 @@ static int _parse_options(const char *key, char *value, pm_printf(ALPM_LOG_DEBUG, "config: logfile: %s\n", value); } } else if(strcmp(key, "XferCommand") == 0) { + char **c; + if((config->xfercommand_argv = _alpm_wordsplit(value)) == NULL) { + pm_printf(ALPM_LOG_WARNING, + _("config file %s, line %d: invalid value for '%s' : '%s'\n"), + file, linenum, "XferCommand", value); + return 1; + } + config->xfercommand_argc = 0; + for(c = config->xfercommand_argv; *c; c++) { + config->xfercommand_argc++; + } config->xfercommand = strdup(value); pm_printf(ALPM_LOG_DEBUG, "config: xfercommand: %s\n", value); } else if(strcmp(key, "CleanMethod") == 0) { diff --git a/src/pacman/conf.h b/src/pacman/conf.h index f45ed436..47df979d 100644 --- a/src/pacman/conf.h +++ b/src/pacman/conf.h @@ -125,6 +125,8 @@ typedef struct __config_t { alpm_list_t *noextract; alpm_list_t *overwrite_files; char *xfercommand; + char **xfercommand_argv; + size_t xfercommand_argc; /* our connection to libalpm */ alpm_handle_t *handle; -- 2.21.0

Signed-off-by: Andrew Gregory --- v2: removes _alpm_prefix and moves to util-common lib/libalpm/hook.c | 119 +-------------------------------------- src/common/util-common.c | 112 ++++++++++++++++++++++++++++++++++++ src/common/util-common.h | 3 + 3 files changed, 118 insertions(+), 116 deletions(-) diff --git a/lib/libalpm/hook.c b/lib/libalpm/hook.c index 6143ea0f..9d1aa215 100644 --- a/lib/libalpm/hook.c +++ b/lib/libalpm/hook.c @@ -17,7 +17,6 @@ * along with this program. If not, see http://www.gnu.org/licenses/. */ -#include #include #include #include @@ -71,23 +70,12 @@ static void _alpm_trigger_free(struct _alpm_trigger_t *trigger) } } -static void _alpm_wordsplit_free(char **ws) -{ - if(ws) { - char **c; - for(c = ws; *c; c++) { - free(*c); - } - free(ws); - } -} - static void _alpm_hook_free(struct _alpm_hook_t *hook) { if(hook) { free(hook->name); free(hook->desc); - _alpm_wordsplit_free(hook->cmd); + wordsplit_free(hook->cmd); alpm_list_free_inner(hook->triggers, (alpm_list_fn_free) _alpm_trigger_free); alpm_list_free(hook->triggers); alpm_list_free(hook->matches); @@ -158,107 +146,6 @@ static int _alpm_hook_validate(alpm_handle_t *handle, return ret; } -static char **_alpm_wordsplit(char *str) -{ - char *c = str, *end; - char **out = NULL, **outsave; - size_t count = 0; - - if(str == NULL) { - errno = EINVAL; - return NULL; - } - - for(c = str; isspace(*c); c++); - while(*c) { - size_t wordlen = 0; - - /* extend our array */ - outsave = out; - if((out = realloc(out, (count + 1) * sizeof(char*))) == NULL) { - out = outsave; - goto error; - } - - /* calculate word length and check for unbalanced quotes */ - for(end = c; *end && !isspace(*end); end++) { - if(*end == '\'' || *end == '"') { - char quote = *end; - while(*(++end) && *end != quote) { - if(*end == '\\' && *(end + 1) == quote) { - end++; - } - wordlen++; - } - if(*end != quote) { - errno = EINVAL; - goto error; - } - } else { - if(*end == '\\' && (end[1] == '\'' || end[1] == '"')) { - end++; /* skip the '\\' */ - } - wordlen++; - } - } - - if(wordlen == (size_t) (end - c)) { - /* no internal quotes or escapes, copy it the easy way */ - if((out[count++] = strndup(c, wordlen)) == NULL) { - goto error; - } - } else { - /* manually copy to remove quotes and escapes */ - char *dest = out[count++] = malloc(wordlen + 1); - if(dest == NULL) { goto error; } - while(c < end) { - if(*c == '\'' || *c == '"') { - char quote = *c; - /* we know there must be a matching end quote, - * no need to check for '\0' */ - for(c++; *c != quote; c++) { - if(*c == '\\' && *(c + 1) == quote) { - c++; - } - *(dest++) = *c; - } - c++; - } else { - if(*c == '\\' && (c[1] == '\'' || c[1] == '"')) { - c++; /* skip the '\\' */ - } - *(dest++) = *(c++); - } - } - *dest = '\0'; - } - - if(*end == '\0') { - break; - } else { - for(c = end + 1; isspace(*c); c++); - } - } - - outsave = out; - if((out = realloc(out, (count + 1) * sizeof(char*))) == NULL) { - out = outsave; - goto error; - } - - out[count++] = NULL; - - return out; - -error: - /* can't use wordsplit_free here because NULL has not been appended */ - while(count) { - free(out[--count]); - } - free(out); - return NULL; -} - static int _alpm_hook_parse_cb(const char *file, int line, const char *section, char *key, char *value, void *data) { @@ -347,9 +234,9 @@ static int _alpm_hook_parse_cb(const char *file, int line, } else if(strcmp(key, "Exec") == 0) { if(hook->cmd != NULL) { warning(_("hook %s line %d: overwriting previous definition of %s\n"), file, line, "Exec"); - _alpm_wordsplit_free(hook->cmd); + wordsplit_free(hook->cmd); } - if((hook->cmd = _alpm_wordsplit(value)) == NULL) { + if((hook->cmd = wordsplit(value)) == NULL) { if(errno == EINVAL) { error(_("hook %s line %d: invalid value %s\n"), file, line, value); } else { diff --git a/src/common/util-common.c b/src/common/util-common.c index 3aa0eac9..fd91ecec 100644 --- a/src/common/util-common.c +++ b/src/common/util-common.c @@ -197,3 +197,115 @@ char *strndup(const char *s, size_t n) return (char *)memcpy(new, s, len); } #endif + +void wordsplit_free(char **ws) +{ + if(ws) { + char **c; + for(c = ws; *c; c++) { + free(*c); + } + free(ws); + } +} + +char **wordsplit(const char *str) +{ + const char *c = str, *end; + char **out = NULL, **outsave; + size_t count = 0; + + if(str == NULL) { + errno = EINVAL; + return NULL; + } + + for(c = str; isspace(*c); c++); + while(*c) { + size_t wordlen = 0; + + /* extend our array */ + outsave = out; + if((out = realloc(out, (count + 1) * sizeof(char*))) == NULL) { + out = outsave; + goto error; + } + + /* calculate word length and check for unbalanced quotes */ + for(end = c; *end && !isspace(*end); end++) { + if(*end == '\'' || *end == '"') { + char quote = *end; + while(*(++end) && *end != quote) { + if(*end == '\\' && *(end + 1) == quote) { + end++; + } + wordlen++; + } + if(*end != quote) { + errno = EINVAL; + goto error; + } + } else { + if(*end == '\\' && (end[1] == '\'' || end[1] == '"')) { + end++; /* skip the '\\' */ + } + wordlen++; + } + } + + if(wordlen == (size_t) (end - c)) { + /* no internal quotes or escapes, copy it the easy way */ + if((out[count++] = strndup(c, wordlen)) == NULL) { + goto error; + } + } else { + /* manually copy to remove quotes and escapes */ + char *dest = out[count++] = malloc(wordlen + 1); + if(dest == NULL) { goto error; } + while(c < end) { + if(*c == '\'' || *c == '"') { + char quote = *c; + /* we know there must be a matching end quote, + * no need to check for '\0' */ + for(c++; *c != quote; c++) { + if(*c == '\\' && *(c + 1) == quote) { + c++; + } + *(dest++) = *c; + } + c++; + } else { + if(*c == '\\' && (c[1] == '\'' || c[1] == '"')) { + c++; /* skip the '\\' */ + } + *(dest++) = *(c++); + } + } + *dest = '\0'; + } + + if(*end == '\0') { + break; + } else { + for(c = end + 1; isspace(*c); c++); + } + } + + outsave = out; + if((out = realloc(out, (count + 1) * sizeof(char*))) == NULL) { + out = outsave; + goto error; + } + + out[count++] = NULL; + + return out; + +error: + /* can't use wordsplit_free here because NULL has not been appended */ + while(count) { + free(out[--count]); + } + free(out); + return NULL; +} diff --git a/src/common/util-common.h b/src/common/util-common.h index 3434e1eb..7ec588cc 100644 --- a/src/common/util-common.h +++ b/src/common/util-common.h @@ -30,6 +30,9 @@ int llstat(char *path, struct stat *buf); char *safe_fgets(char *s, int size, FILE *stream); +void wordsplit_free(char **ws); +char **wordsplit(const char *str); + size_t strtrim(char *str); #ifndef HAVE_STRNDUP -- 2.23.0

system() runs the provided command via a shell, which is subject to command injection. Even though pacman already provides a mechanism to sign and verify the databases containing the urls, certain distributions have yet to get their act together and start signing databases, leaving them vulnerable to MITM attacks. Replacing the system call with an almost equivalent exec call removes the possibility of a shell-injection attack for those users. Signed-off-by: Andrew Gregory --- v2: * properly deal with signals * pass errno via pipe instead of mmap * fix debug logging src/pacman/conf.c | 129 ++++++++++++++++++++++++---- src/pacman/conf.h | 2 + test/pacman/tests/sync200.py | 2 +- test/pacman/tests/xfercommand001.py | 2 +- 4 files changed, 116 insertions(+), 19 deletions(-) diff --git a/src/pacman/conf.c b/src/pacman/conf.c index 2d8518c4..9a39bba9 100644 --- a/src/pacman/conf.c +++ b/src/pacman/conf.c @@ -29,6 +29,7 @@ #include #include #include /* uname */ +#include #include /* pacman */ @@ -153,6 +154,7 @@ int config_free(config_t *oldconfig) free(oldconfig->print_format); free(oldconfig->arch); free(oldconfig); + wordsplit_free(oldconfig->xfercommand_argv); return 0; } @@ -201,18 +203,86 @@ static char *get_tempfile(const char *path, const char *filename) return tempfile; } +/* system()/exec() hybrid function allowing exec()-style direct execution + * of a command with the simplicity of system() + * - not thread-safe + * - errno may be set by fork(), pipe(), or execvp() + */ +static int systemvp(const char *file, char *const argv[]) +{ + int pid, err = 0, ret = -1, err_fd[2]; + sigset_t oldblock; + struct sigaction sa_ign = { .sa_handler = SIG_IGN }, oldint, oldquit; + + if(pipe(err_fd) != 0) { + return -1; + } + + sigaction(SIGINT, &sa_ign, &oldint); + sigaction(SIGQUIT, &sa_ign, &oldquit); + sigaddset(&sa_ign.sa_mask, SIGCHLD); + sigprocmask(SIG_BLOCK, &sa_ign.sa_mask, &oldblock); + + pid = fork(); + + /* child */ + if(pid == 0) { + close(err_fd[0]); + fcntl(err_fd[1], F_SETFD, FD_CLOEXEC); + + /* restore signal handling for the child to inherit */ + sigaction(SIGINT, &oldint, NULL); + sigaction(SIGQUIT, &oldquit, NULL); + sigprocmask(SIG_SETMASK, &oldblock, NULL); + + execvp(file, argv); + + /* execvp failed, pass the error back to the parent */ + while(write(err_fd[1], &errno, sizeof(errno)) == -1 && errno == EINTR); + _Exit(127); + } + + /* parent */ + close(err_fd[1]); + + if(pid != -1) { + int wret; + while((wret = waitpid(pid, &ret, 0)) == -1 && errno == EINTR); + if(wret > 0) { + while(read(err_fd[0], &err, sizeof(err)) == -1 && errno == EINTR); + } + } else { + /* fork failed, make sure errno is preserved after cleanup */ + err = errno; + } + + close(err_fd[0]); + + sigaction(SIGINT, &oldint, NULL); + sigaction(SIGQUIT, &oldquit, NULL); + sigprocmask(SIG_SETMASK, &oldblock, NULL); + + if(err) { + errno = err; + ret = -1; + } + + return ret; +} + /** External fetch callback */ static int download_with_xfercommand(const char *url, const char *localpath, int force) { int ret = 0, retval; int usepart = 0; - int cwdfd; + int cwdfd = -1; struct stat st; - char *parsedcmd, *tempcmd; char *destfile, *tempfile, *filename; + const char **argv; + size_t i; - if(!config->xfercommand) { + if(!config->xfercommand_argv) { return -1; } @@ -230,17 +300,26 @@ static int download_with_xfercommand(const char *url, const char *localpath, unlink(destfile); } - tempcmd = strdup(config->xfercommand); - /* replace all occurrences of %o with fn.part */ - if(strstr(tempcmd, "%o")) { - usepart = 1; - parsedcmd = strreplace(tempcmd, "%o", tempfile); - free(tempcmd); - tempcmd = parsedcmd; + if((argv = calloc(config->xfercommand_argc + 1, sizeof(char*))) == NULL) { + size_t bytes = (config->xfercommand_argc + 1) * sizeof(char*); + pm_printf(ALPM_LOG_ERROR, + _n("malloc failure: could not allocate %zu byte\n", + "malloc failure: could not allocate %zu bytes\n", + bytes), + bytes); + goto cleanup; + } + + for(i = 0; i <= config->xfercommand_argc; i++) { + const char *val = config->xfercommand_argv[i]; + if(val && strcmp(val, "%o") == 0) { + usepart = 1; + val = tempfile; + } else if(val && strcmp(val, "%u") == 0) { + val = url; + } + argv[i] = val; } - /* replace all occurrences of %u with the download URL */ - parsedcmd = strreplace(tempcmd, "%u", url); - free(tempcmd); /* save the cwd so we can restore it later */ do { @@ -256,9 +335,15 @@ static int download_with_xfercommand(const char *url, const char *localpath, ret = -1; goto cleanup; } - /* execute the parsed command via /bin/sh -c */ - pm_printf(ALPM_LOG_DEBUG, "running command: %s\n", parsedcmd); - retval = system(parsedcmd); + + if(config->logmask & ALPM_LOG_DEBUG) { + char *cmd = arg_to_string(config->xfercommand_argc, (char**)argv); + if(cmd) { + pm_printf(ALPM_LOG_DEBUG, "running command: %s\n", cmd); + free(cmd); + } + } + retval = systemvp(argv[0], (char**)argv); if(retval == -1) { pm_printf(ALPM_LOG_WARNING, _("running XferCommand: fork failed!\n")); @@ -296,7 +381,6 @@ cleanup: } free(destfile); free(tempfile); - free(parsedcmd); return ret; } @@ -544,6 +628,17 @@ static int _parse_options(const char *key, char *value, pm_printf(ALPM_LOG_DEBUG, "config: logfile: %s\n", value); } } else if(strcmp(key, "XferCommand") == 0) { + char **c; + if((config->xfercommand_argv = wordsplit(value)) == NULL) { + pm_printf(ALPM_LOG_WARNING, + _("config file %s, line %d: invalid value for '%s' : '%s'\n"), + file, linenum, "XferCommand", value); + return 1; + } + config->xfercommand_argc = 0; + for(c = config->xfercommand_argv; *c; c++) { + config->xfercommand_argc++; + } config->xfercommand = strdup(value); pm_printf(ALPM_LOG_DEBUG, "config: xfercommand: %s\n", value); } else if(strcmp(key, "CleanMethod") == 0) { diff --git a/src/pacman/conf.h b/src/pacman/conf.h index f45ed436..47df979d 100644 --- a/src/pacman/conf.h +++ b/src/pacman/conf.h @@ -125,6 +125,8 @@ typedef struct __config_t { alpm_list_t *noextract; alpm_list_t *overwrite_files; char *xfercommand; + char **xfercommand_argv; + size_t xfercommand_argc; /* our connection to libalpm */ alpm_handle_t *handle; diff --git a/test/pacman/tests/sync200.py b/test/pacman/tests/sync200.py index 2bcdd5d3..18f38b81 100644 --- a/test/pacman/tests/sync200.py +++ b/test/pacman/tests/sync200.py @@ -1,6 +1,6 @@ self.description = "Synchronize the local database" -self.option['XferCommand'] = ['/usr/bin/curl %u > %o'] +self.option['XferCommand'] = ['/usr/bin/curl %u -o %o'] sp1 = pmpkg("spkg1", "1.0-1") sp1.depends = ["spkg2"] diff --git a/test/pacman/tests/xfercommand001.py b/test/pacman/tests/xfercommand001.py index 0d244dc6..0ac99080 100644 --- a/test/pacman/tests/xfercommand001.py +++ b/test/pacman/tests/xfercommand001.py @@ -3,7 +3,7 @@ # this setting forces us to download packages self.cachepkgs = False #wget doesn't support file:// urls. curl does -self.option['XferCommand'] = ['/usr/bin/curl %u > %o'] +self.option['XferCommand'] = ['/usr/bin/curl %u -o %o'] numpkgs = 10 pkgnames = [] -- 2.23.0

On 12/10/19 1:45 pm, Andrew Gregory wrote:

system() runs the provided command via a shell, which is subject to command injection. Even though pacman already provides a mechanism to sign and verify the databases containing the urls, certain distributions have yet to get their act together and start signing databases, leaving them vulnerable to MITM attacks. Replacing the system call with an almost equivalent exec call removes the possibility of a shell-injection attack for those users.

Signed-off-by: Andrew Gregory --- v2: * properly deal with signals * pass errno via pipe instead of mmap * fix debug logging

src/pacman/conf.c | 129 ++++++++++++++++++++++++---- src/pacman/conf.h | 2 + test/pacman/tests/sync200.py | 2 +- test/pacman/tests/xfercommand001.py | 2 +- 4 files changed, 116 insertions(+), 19 deletions(-)

diff --git a/src/pacman/conf.c b/src/pacman/conf.c index 2d8518c4..9a39bba9 100644 --- a/src/pacman/conf.c +++ b/src/pacman/conf.c @@ -29,6 +29,7 @@ #include #include #include /* uname */ +#include #include

/* pacman */ @@ -153,6 +154,7 @@ int config_free(config_t *oldconfig) free(oldconfig->print_format); free(oldconfig->arch); free(oldconfig); + wordsplit_free(oldconfig->xfercommand_argv);

This line needs to be one higher. A

On 10/12/19 at 09:11pm, Allan McRae wrote:

On 12/10/19 1:45 pm, Andrew Gregory wrote:

...

system() runs the provided command via a shell, which is subject to command injection. Even though pacman already provides a mechanism to sign and verify the databases containing the urls, certain distributions have yet to get their act together and start signing databases, leaving them vulnerable to MITM attacks. Replacing the system call with an almost equivalent exec call removes the possibility of a shell-injection attack for those users.

Signed-off-by: Andrew Gregory

<snip>

...

@@ -230,17 +300,26 @@ static int download_with_xfercommand(const char *url, const char *localpath, unlink(destfile); }

- tempcmd = strdup(config->xfercommand); - /* replace all occurrences of %o with fn.part */ - if(strstr(tempcmd, "%o")) { - usepart = 1; - parsedcmd = strreplace(tempcmd, "%o", tempfile); - free(tempcmd); - tempcmd = parsedcmd; + if((argv = calloc(config->xfercommand_argc + 1, sizeof(char*))) == NULL) {

need to free this at the end.

Updated patch pushed to my repo that fixes this and the misplaced free and also corrects the indenting in systemvp to use tabs.