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various: try to use DEFAULT_USER_SHELL for root too

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/bin/sh as a shell is punishing. There is no good reason to make
the occasional root login unpleasant.

Since /bin/sh is usually /bin/bash in compat mode, i.e. if one is
available, the other will be too, /bin/bash is almost as good as a default.
But to avoid a regression in the situation where /bin/bash (or
DEFAULT_USER_SHELL) is not installed, we check with access() and fall back
to /bin/sh. This should make this change in behaviour less risky.

(FWIW, e.g. Fedora/RHEL use /bin/bash as default for root.)

This is a follow-up of sorts for 53350c7bba,
which added the default-user-shell option, but most likely with the idea
of using /bin/bash less ;)

Fixes #24369.
This commit is contained in:
Zbigniew Jędrzejewski-Szmek
2022-08-24 10:02:46 +02:00
parent 5f465fda4e
commit 8a7adccbdb
9 changed files with 59 additions and 37 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/nss-systemd/nss-systemd.c
+33 -27
View File
@@ -26,7 +26,7 @@ static const struct passwd root_passwd = {
.pw_gid = 0,
.pw_gecos = (char*) "Super User",
.pw_dir = (char*) "/root",
.pw_shell = (char*) "/bin/sh",
.pw_shell = NULL,
};
static const struct spwd root_spwd = {
@@ -142,24 +142,25 @@ NSS_INITGROUPS_PROTOTYPE(systemd);
static enum nss_status copy_synthesized_passwd(
struct passwd *dest,
const struct passwd *src,
const char *fallback_shell,
char *buffer, size_t buflen,
int *errnop) {
size_t required;
assert(dest);
assert(src);
assert(src->pw_name);
assert(src->pw_passwd);
assert(src->pw_gecos);
assert(src->pw_dir);
assert(src->pw_shell);
required = strlen(src->pw_name) + 1;
required += strlen(src->pw_passwd) + 1;
required += strlen(src->pw_gecos) + 1;
required += strlen(src->pw_dir) + 1;
required += strlen(src->pw_shell) + 1;
const char *shell = ASSERT_PTR(src->pw_shell ?: fallback_shell);
size_t required =
strlen(src->pw_name) + 1 +
strlen(src->pw_passwd) + 1 +
strlen(src->pw_gecos) + 1 +
strlen(src->pw_dir) + 1 +
strlen(shell) + 1;
if (buflen < required) {
*errnop = ERANGE;
@@ -176,7 +177,7 @@ static enum nss_status copy_synthesized_passwd(
dest->pw_gecos = stpcpy(dest->pw_passwd, src->pw_passwd) + 1;
dest->pw_dir = stpcpy(dest->pw_gecos, src->pw_gecos) + 1;
dest->pw_shell = stpcpy(dest->pw_dir, src->pw_dir) + 1;
strcpy(dest->pw_shell, src->pw_shell);
strcpy(dest->pw_shell, shell);
return NSS_STATUS_SUCCESS;
}
@@ -187,15 +188,14 @@ static enum nss_status copy_synthesized_spwd(
char *buffer, size_t buflen,
int *errnop) {
size_t required;
assert(dest);
assert(src);
assert(src->sp_namp);
assert(src->sp_pwdp);
required = strlen(src->sp_namp) + 1;
required += strlen(src->sp_pwdp) + 1;
size_t required =
strlen(src->sp_namp) + 1 +
strlen(src->sp_pwdp) + 1;
if (buflen < required) {
*errnop = ERANGE;
@@ -220,8 +220,6 @@ static enum nss_status copy_synthesized_group(
char *buffer, size_t buflen,
int *errnop) {
size_t required;
assert(dest);
assert(src);
assert(src->gr_name);
@@ -229,9 +227,10 @@ static enum nss_status copy_synthesized_group(
assert(src->gr_mem);
assert(!*src->gr_mem); /* Our synthesized records' gr_mem is always just NULL... */
required = strlen(src->gr_name) + 1;
required += strlen(src->gr_passwd) + 1;
required += sizeof(char*); /* ...but that NULL still needs to be stored into the buffer! */
size_t required =
strlen(src->gr_name) + 1 +
strlen(src->gr_passwd) + 1 +
sizeof(char*); /* ...but that NULL still needs to be stored into the buffer! */
if (buflen < ALIGN(required)) {
*errnop = ERANGE;
@@ -257,15 +256,14 @@ static enum nss_status copy_synthesized_sgrp(
char *buffer, size_t buflen,
int *errnop) {
size_t required;
assert(dest);
assert(src);
assert(src->sg_namp);
assert(src->sg_passwd);
required = strlen(src->sg_namp) + 1;
required += strlen(src->sg_passwd) + 1;
size_t required =
strlen(src->sg_namp) + 1 +
strlen(src->sg_passwd) + 1;
if (buflen < required) {
*errnop = ERANGE;
@@ -310,13 +308,17 @@ enum nss_status _nss_systemd_getpwnam_r(
if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_SYNTHETIC") <= 0) {
if (streq(name, root_passwd.pw_name))
return copy_synthesized_passwd(pwd, &root_passwd, buffer, buflen, errnop);
return copy_synthesized_passwd(pwd, &root_passwd,
default_root_shell(NULL),
buffer, buflen, errnop);
if (streq(name, nobody_passwd.pw_name)) {
if (!synthesize_nobody())
return NSS_STATUS_NOTFOUND;
return copy_synthesized_passwd(pwd, &nobody_passwd, buffer, buflen, errnop);
return copy_synthesized_passwd(pwd, &nobody_passwd,
NULL,
buffer, buflen, errnop);
}
} else if (STR_IN_SET(name, root_passwd.pw_name, nobody_passwd.pw_name))
@@ -354,13 +356,17 @@ enum nss_status _nss_systemd_getpwuid_r(
if (getenv_bool_secure("SYSTEMD_NSS_BYPASS_SYNTHETIC") <= 0) {
if (uid == root_passwd.pw_uid)
return copy_synthesized_passwd(pwd, &root_passwd, buffer, buflen, errnop);
return copy_synthesized_passwd(pwd, &root_passwd,
default_root_shell(NULL),
buffer, buflen, errnop);
if (uid == nobody_passwd.pw_uid) {
if (!synthesize_nobody())
return NSS_STATUS_NOTFOUND;
return copy_synthesized_passwd(pwd, &nobody_passwd, buffer, buflen, errnop);
return copy_synthesized_passwd(pwd, &nobody_passwd,
NULL,
buffer, buflen, errnop);
}
} else if (uid == root_passwd.pw_uid || uid == nobody_passwd.pw_uid)