1 files changed, 223 insertions, 0 deletions
diff --git a/libmisc/idmapping.c b/libmisc/idmapping.c
new file mode 100644
index 0000000..30eb89f
--- /dev/null
+++ b/libmisc/idmapping.c
@@ -0,0 +1,223 @@
+/*
+ * SPDX-FileCopyrightText: 2013 Eric Biederman
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <config.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include "prototypes.h"
+#include "idmapping.h"
+#if HAVE_SYS_CAPABILITY_H
+#include <sys/prctl.h>
+#include <sys/capability.h>
+#endif
+#include "shadowlog.h"
+
+struct map_range *get_map_ranges(int ranges, int argc, char **argv)
+{
+	struct map_range *mappings, *mapping;
+	int idx, argidx;
+
+	if (ranges < 0 || argc < 0) {
+		fprintf(log_get_logfd(), "%s: error calculating number of arguments\n", log_get_progname());
+		return NULL;
+	}
+
+	if (ranges != ((argc + 2) / 3)) {
+		fprintf(log_get_logfd(), "%s: ranges: %u is wrong for argc: %d\n", log_get_progname(), ranges, argc);
+		return NULL;
+	}
+
+	if ((ranges * 3) > argc) {
+		fprintf(log_get_logfd(), "ranges: %u argc: %d\n",
+			ranges, argc);
+		fprintf(log_get_logfd(),
+			_( "%s: Not enough arguments to form %u mappings\n"),
+			log_get_progname(), ranges);
+		return NULL;
+	}
+
+	mappings = calloc(ranges, sizeof(*mappings));
+	if (!mappings) {
+		fprintf(log_get_logfd(), _( "%s: Memory allocation failure\n"),
+			log_get_progname());
+		exit(EXIT_FAILURE);
+	}
+
+	/* Gather up the ranges from the command line */
+	mapping = mappings;
+	for (idx = 0, argidx = 0; idx < ranges; idx++, argidx += 3, mapping++) {
+		if (!getulong(argv[argidx + 0], &mapping->upper)) {
+			free(mappings);
+			return NULL;
+		}
+		if (!getulong(argv[argidx + 1], &mapping->lower)) {
+			free(mappings);
+			return NULL;
+		}
+		if (!getulong(argv[argidx + 2], &mapping->count)) {
+			free(mappings);
+			return NULL;
+		}
+		if (ULONG_MAX - mapping->upper <= mapping->count || ULONG_MAX - mapping->lower <= mapping->count) {
+			fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+		if (mapping->upper > UINT_MAX ||
+			mapping->lower > UINT_MAX ||
+			mapping->count > UINT_MAX)  {
+			fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+		if (mapping->lower + mapping->count > UINT_MAX ||
+				mapping->upper + mapping->count > UINT_MAX) {
+			fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+		if (mapping->lower + mapping->count < mapping->lower ||
+				mapping->upper + mapping->count < mapping->upper) {
+			/* this one really shouldn't be possible given previous checks */
+			fprintf(log_get_logfd(), _( "%s: subuid overflow detected.\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+	}
+	return mappings;
+}
+
+/* Number of ascii digits needed to print any unsigned long in decimal.
+ * There are approximately 10 bits for every 3 decimal digits.
+ * So from bits to digits the formula is roundup((Number of bits)/10) * 3.
+ * For common sizes of integers this works out to:
+ *  2bytes -->  6 ascii estimate  -> 65536  (5 real)
+ *  4bytes --> 12 ascii estimated -> 4294967296 (10 real)
+ *  8bytes --> 21 ascii estimated -> 18446744073709551616 (20 real)
+ * 16bytes --> 39 ascii estimated -> 340282366920938463463374607431768211456 (39 real)
+ */
+#define ULONG_DIGITS ((((sizeof(unsigned long) * CHAR_BIT) + 9)/10)*3)
+
+#if HAVE_SYS_CAPABILITY_H
+static inline bool maps_lower_root(int cap, int ranges, const struct map_range *mappings)
+{
+	int idx;
+	const struct map_range *mapping;
+
+	if (cap != CAP_SETUID)
+		return false;
+
+	mapping = mappings;
+	for (idx = 0; idx < ranges; idx++, mapping++) {
+		if (mapping->lower == 0)
+			return true;
+	}
+
+	return false;
+}
+#endif
+
+/*
+ * The ruid refers to the caller's uid and is used to reset the effective uid
+ * back to the callers real uid.
+ * This clutch mainly exists for setuid-based new{g,u}idmap binaries that are
+ * called in contexts where all capabilities other than the necessary
+ * CAP_SET{G,U}ID capabilities are dropped. Since the kernel will require
+ * assurance that the caller holds CAP_SYS_ADMIN over the target user namespace
+ * the only way it can confirm is in this case is if the effective uid is
+ * equivalent to the uid owning the target user namespace.
+ * Note, we only support this when a) new{g,u}idmap is not called by root and
+ * b) if the caller's uid and the uid retrieved via system appropriate means
+ * (shadow file or other) are identical. Specifically, this does not support
+ * when the root user calls the new{g,u}idmap binary for an unprivileged user.
+ * If this is wanted: use file capabilities!
+ */
+void write_mapping(int proc_dir_fd, int ranges, const struct map_range *mappings,
+	const char *map_file, uid_t ruid)
+{
+	int idx;
+	const struct map_range *mapping;
+	size_t bufsize;
+	char *buf, *pos;
+	int fd;
+
+#if HAVE_SYS_CAPABILITY_H
+	int cap;
+	struct __user_cap_header_struct hdr = {_LINUX_CAPABILITY_VERSION_3, 0};
+	struct __user_cap_data_struct data[2] = {{0}};
+
+	if (strcmp(map_file, "uid_map") == 0) {
+		cap = CAP_SETUID;
+	} else if (strcmp(map_file, "gid_map") == 0) {
+		cap = CAP_SETGID;
+	} else {
+		fprintf(log_get_logfd(), _("%s: Invalid map file %s specified\n"), log_get_progname(), map_file);
+		exit(EXIT_FAILURE);
+	}
+
+	/* Align setuid- and fscaps-based new{g,u}idmap behavior. */
+	if (geteuid() == 0 && geteuid() != ruid) {
+		if (prctl(PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0) {
+			fprintf(log_get_logfd(), _("%s: Could not prctl(PR_SET_KEEPCAPS)\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+
+		if (seteuid(ruid) < 0) {
+			fprintf(log_get_logfd(), _("%s: Could not seteuid to %d\n"), log_get_progname(), ruid);
+			exit(EXIT_FAILURE);
+		}
+	}
+
+	/* Lockdown new{g,u}idmap by dropping all unneeded capabilities. */
+	memset(data, 0, sizeof(data));
+	data[0].effective = CAP_TO_MASK(cap);
+	/*
+	 * When uid 0 from the ancestor userns is supposed to be mapped into
+	 * the child userns we need to retain CAP_SETFCAP.
+	 */
+	if (maps_lower_root(cap, ranges, mappings))
+		data[0].effective |= CAP_TO_MASK(CAP_SETFCAP);
+	data[0].permitted = data[0].effective;
+	if (capset(&hdr, data) < 0) {
+		fprintf(log_get_logfd(), _("%s: Could not set caps\n"), log_get_progname());
+		exit(EXIT_FAILURE);
+	}
+#endif
+
+	bufsize = ranges * ((ULONG_DIGITS + 1) * 3);
+	pos = buf = xmalloc(bufsize);
+
+	/* Build the mapping command */
+	mapping = mappings;
+	for (idx = 0; idx < ranges; idx++, mapping++) {
+		/* Append this range to the string that will be written */
+		int written = snprintf(pos, bufsize - (pos - buf),
+			"%lu %lu %lu\n",
+			mapping->upper,
+			mapping->lower,
+			mapping->count);
+		if ((written <= 0) || (written >= (bufsize - (pos - buf)))) {
+			fprintf(log_get_logfd(), _("%s: snprintf failed!\n"), log_get_progname());
+			exit(EXIT_FAILURE);
+		}
+		pos += written;
+	}
+
+	/* Write the mapping to the mapping file */
+	fd = openat(proc_dir_fd, map_file, O_WRONLY);
+	if (fd < 0) {
+		fprintf(log_get_logfd(), _("%s: open of %s failed: %s\n"),
+			log_get_progname(), map_file, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	if (write(fd, buf, pos - buf) != (pos - buf)) {
+		fprintf(log_get_logfd(), _("%s: write to %s failed: %s\n"),
+			log_get_progname(), map_file, strerror(errno));
+		exit(EXIT_FAILURE);
+	}
+	close(fd);
+	free(buf);
+}