diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..98ed9b6 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,5 @@ +* text eol=lf + +su-exec -text +su-exec-shared -text +su-exec-static -text diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..3f3c1d1 --- /dev/null +++ b/.gitignore @@ -0,0 +1,9 @@ +.* +*~ + +*.out +*.so + +su-exec +su-exec-shared +su-exec-static diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..d645695 --- /dev/null +++ b/LICENSE @@ -0,0 +1,202 @@ + + Apache License + Version 2.0, January 2004 + http://www.apache.org/licenses/ + + TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION + + 1. 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We also recommend that a + file or class name and description of purpose be included on the + same "printed page" as the copyright notice for easier + identification within third-party archives. + + Copyright [yyyy] [name of copyright owner] + + Licensed under the Apache License, Version 2.0 (the "License"); + you may not use this file except in compliance with the License. + You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..a3e1988 --- /dev/null +++ b/Makefile @@ -0,0 +1,18 @@ +CFLAGS ?= -Os -Wall -Wextra -pedantic +LDFLAGS ?= + +PROG := su-exec +SRCS := $(PROG).c + +all: $(PROG)-shared $(PROG)-static + +$(PROG)-shared: $(SRCS) + $(CC) $(CFLAGS) -s -o $@ $^ $(LDFLAGS) + ldd -v $@ + +$(PROG)-static: $(SRCS) + $(CC) $(CFLAGS) -s -o $@ $^ $(LDFLAGS) -static + /bin/cp $(PROG)-static $(PROG) + +clean: + rm -f $(PROG) $(PROG)-shared $(PROG)-static diff --git a/README.md b/README.md new file mode 100644 index 0000000..5f4d2ee --- /dev/null +++ b/README.md @@ -0,0 +1,63 @@ +# su-exec +switch user and group, then exec. + +[`su-exec`](https://github.com/songdongsheng/su-exec) is a very minimal re-write of +[`gosu`](https://github.com/tianon/gosu) in C, making for a much smaller binary. + +## Purpose +This is a simple tool that will simply execute a program with different +privileges. The program will be executed directly and not run as a child, +like su and sudo does, which avoids TTY and signal issues. + +Notice that su-exec depends on being **run by the root user**, non-root +users do not have permission to change uid/gid. + +## Usage + +```shell +su-exec user-spec command [ arguments... ] +``` + +`user-spec` is either a user name (e.g. `nobody`) or user name and group +name separated with colon (e.g. `ftp:ftp`). Numeric uid/gid values +can be used instead of names. + +```shell +$ su-exec nginx:122 /usr/sbin/nginx -c /etc/nginx/nginx.conf +``` + +## Why reinvent gosu/su-exec ? + +This does more or less exactly the same thing as [gosu](https://github.com/tianon/gosu) +but it is only 0.6MB (7KB for shared version) instead of 2.2MB. +In particular, the simple C program has a smaller attack plane. + +The [`ncopa's su-exec`](https://github.com/ncopa/su-exec) have critical bugs (or features), +it will **use root permission silently** if given invalid user-spec ! + +# Download from IPFS (InterPlanetary File System) +## IPFS hash +``` +# touch -d "1970-01-01 00:00:00" su-exec-shared su-exec-static + +# ls -la su-exec-shared su-exec-static +-rwxr-xr-x 1 root root 6960 Jan 1 1970 su-exec-shared +-rwxr-xr-x 1 root root 609376 Jan 1 1970 su-exec-static + +# ipfs add su-exec-shared su-exec-static +added QmWcck5mQqbzcEx8mM6bdDestYwqiwsXkCVa97odggk9Vy su-exec-shared +added QmX3bzvCM3cxFFWGGMhQnMV214HLzyFceD6Vyf2aRYW7NB su-exec-static +``` + +## Download from IPFS +``` +# ipfs get -o su-exec-shared QmWcck5mQqbzcEx8mM6bdDestYwqiwsXkCVa97odggk9Vy +# ipfs get -o su-exec-static QmX3bzvCM3cxFFWGGMhQnMV214HLzyFceD6Vyf2aRYW7NB +``` + +## Download from IPFS gateway +### cloudflare-ipfs.com +``` +curl -o su-exec-shared https://cloudflare-ipfs.com/ipfs/QmWcck5mQqbzcEx8mM6bdDestYwqiwsXkCVa97odggk9Vy +curl -o su-exec-static https://cloudflare-ipfs.com/ipfs/QmX3bzvCM3cxFFWGGMhQnMV214HLzyFceD6Vyf2aRYW7NB +``` diff --git a/su-exec.c b/su-exec.c new file mode 100644 index 0000000..7abc00a --- /dev/null +++ b/su-exec.c @@ -0,0 +1,132 @@ +/* + * switch user and group, then exec. + * + * indent -linux -cs -nut -i 4 -l 120 su-exec.c + * clang-format -style=file -i su-exec.c + * cc -O2 -std=gnu99 -Wall -Wextra -pedantic -o su-exec su-exec.c + * + * http://man7.org/linux/man-pages/dir_all_alphabetic.html + */ + +#include + +#include +#include +#include +#include +#include +#include +#include +#include + +int main(int argc, char *argv[]) +{ + char *end; + + if (argc < 3) { + printf("Usage: su-exec user-spec command [args]\n"); + printf(" eg: su-exec tianon bash\n"); + printf(" su-exec nobody:root bash -c 'whoami && id'\n"); + printf(" su-exec 1000:1 id\n"); + printf("\n"); + printf("su-exec license: Apache License, Version 2.0\n"); + exit(1); + } + + /* get user and group part from user-spec */ + char *user = argv[1]; + char *group = strchr(user, ':'); + if (group) { + *group++ = '\0'; + } + + if (user[0] == '\0') { + printf("invalid user-spec, user part needed\n"); + exit(1); + } + + /* get passwd entry */ + struct passwd *pw = NULL; + if (user[0] != '\0') { + pw = getpwnam(user); + uid_t nuid = strtol(user, &end, 10); + if (*end == '\0') { + pw = getpwuid(nuid); + } + } + if (pw == NULL) { + printf("invalid user-spec, user '%s' not found\n", user); + exit(1); + } + + uid_t uid = pw->pw_uid; + gid_t gid = pw->pw_gid; + + /* set variable HOME and USER in the environment */ + setenv("HOME", pw->pw_dir != NULL ? pw->pw_dir : "/", 1); + setenv("USER", pw->pw_name, 1); + + /* get group entry */ + if (group && group[0] != '\0') { + /* group was specified, ignore grouplist for setgroups later */ + pw = NULL; + + struct group *gr = getgrnam(group); + if (gr == NULL) { + gid_t ngid = strtol(group, &end, 10); + if (*end == '\0') { + gr = getgrgid(ngid); + if (gr == NULL) + gid = ngid; + } + } + if (gr != NULL) + gid = gr->gr_gid; + else { + printf("invalid user-spec, group '%s' not found\n", group); + exit(1); + } + } + + /* setgroups */ + if (pw == NULL) { + /* group was specified */ + if (setgroups(1, &gid) < 0) + err(1, "setgroups(%i)", gid); + } else { + /* group was not specified */ + int ngroups = 0; + gid_t *glist = NULL; + + while (1) { + int r = getgrouplist(pw->pw_name, gid, glist, &ngroups); + + if (r >= 0) { + if (setgroups(ngroups, glist) < 0) + err(1, "setgroups"); + break; + } + + glist = realloc(glist, ngroups * sizeof(gid_t)); + if (glist == NULL) + err(1, "malloc"); + } + free(glist); + } + + /* setgid */ + if (setgid(gid) < 0) + err(1, "setgid(%i)", gid); + + /* setuid */ + if (setuid(uid) < 0) + err(1, "setuid(%i)", uid); + + /* exec */ + execvp(argv[2], &argv[2]); + + /* error has occurred */ + err(1, "%s", argv[2]); + + return 1; +}