[Libguestfs] [libnbd PATCH v5 1/4] socket activation: generalize environment construction
Laszlo Ersek
lersek at redhat.com
Sat Mar 25 11:39:26 UTC 2023
In the future, we'd like to add systemd socket activation environment
variables such that:
- their values may not be constants (not even for pre-allocating space),
- they may be optional,
- regardless of some optional variables being added or not, the positions
of those that we do add can be captured, for later reference.
Generalize prepare_socket_activation_environment() accordingly. Write the
child PID to "LISTEN_PID=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" with the new
"capturing" interface.
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
Reviewed-by: Richard W.M. Jones <rjones at redhat.com>
Reviewed-by: Eric Blake <eblake at redhat.com>
---
Notes:
v5:
- pick up Eric's R-b
v4:
- pick up Rich's R-b
- resolve rebase conflicts (a) inside
prepare_socket_activation_environment(), (b) near the
prepare_socket_activation_environment() call site -- due to keeping
set_error() internal to prepare_socket_activation_environment(), in
patch "socket activation: clean up responsibilities of
prep.sock.act.env.()"
context:-U6
generator/states-connect-socket-activation.c | 160 +++++++++++++++-----
1 file changed, 125 insertions(+), 35 deletions(-)
diff --git a/generator/states-connect-socket-activation.c b/generator/states-connect-socket-activation.c
index a214ffd5a6e4..10ccc3119299 100644
--- a/generator/states-connect-socket-activation.c
+++ b/generator/states-connect-socket-activation.c
@@ -27,85 +27,169 @@
#include <errno.h>
#include <assert.h>
#include <sys/socket.h>
#include <sys/un.h>
#include "internal.h"
+#include "compiler-macros.h"
+#include "unique-name.h"
+#include "array-size.h"
+#include "checked-overflow.h"
/* This is baked into the systemd socket activation API. */
#define FIRST_SOCKET_ACTIVATION_FD 3
-/* == strlen ("LISTEN_PID=") | strlen ("LISTEN_FDS=") */
-#define PREFIX_LENGTH 11
+/* Describes a systemd socket activation environment variable. */
+struct sact_var {
+ const char *prefix; /* variable name and equal sign */
+ size_t prefix_len;
+ const char *value;
+ size_t value_len;
+};
+
+/* Determine the length of a string, using "sizeof" whenever possible.
+ *
+ * Do not use this macro on an argument that has side effects, as no guarantees
+ * are given regarding the number of times the argument may be evaluated.
+ * TYPE_IS_ARRAY(s) itself may contribute a different number of evaluations
+ * dependent on whether "s" has variably modified type, and then the conditional
+ * operator either evaluates "sizeof s" (which contributes 0 or 1 evaluations,
+ * dependent on whether "s" has variably modified type) or strlen(s) (which
+ * contributes 1 evaluation). Also note that the argument of the "sizeof"
+ * operator is *only* parenthesized because "s" is a macro parameter here.
+*/
+#define STRLEN1(s) ((TYPE_IS_ARRAY (s) ? sizeof (s) - 1 : strlen (s)))
+
+/* Push a new element to an array of "sact_var" structures.
+ *
+ * "vars" is the array to extend. "num_vars" (of type (size_t *)) points to the
+ * number of elements that the array, on input, contains; (*num_vars) is
+ * increased by one on output. "prefix" and "value" serve as the values for
+ * setting the fields in the new element. "ofs" (of type (size_t *)) may be
+ * NULL; if it isn't, then on output, (*ofs) is set to the input value of
+ * (*num_vars): the offset of the just-pushed element.
+ *
+ * Avoid arguments with side-effects here as well.
+ */
+#define SACT_VAR_PUSH(vars, num_vars, prefix, value, ofs) \
+ SACT_VAR_PUSH1 ((vars), (num_vars), (prefix), (value), (ofs), \
+ NBDKIT_UNIQUE_NAME (_ofs))
+#define SACT_VAR_PUSH1(vars, num_vars, prefix, value, ofs, ofs1) \
+ do { \
+ size_t *ofs1; \
+ \
+ assert (*(num_vars) < ARRAY_SIZE (vars)); \
+ ofs1 = (ofs); \
+ if (ofs1 != NULL) \
+ *ofs1 = *(num_vars); \
+ (vars)[(*(num_vars))++] = (struct sact_var){ (prefix), STRLEN1 (prefix), \
+ (value), STRLEN1 (value) }; \
+ } while (0)
extern char **environ;
-/* Prepare environment for calling execvp when doing systemd socket
- * activation. Takes the current environment and copies it. Removes
- * any existing LISTEN_PID or LISTEN_FDS and replaces them with new
- * variables. env[0] is "LISTEN_PID=..." which is filled in by
- * CONNECT_SA.START, and env[1] is "LISTEN_FDS=1".
+/* Prepare environment for calling execvp when doing systemd socket activation.
+ * Takes the current environment and copies it. Removes any existing socket
+ * activation variables and replaces them with new ones. Variables in "sact_var"
+ * will be placed at the front of "env", preserving the order from "sact_var".
*/
static int
-prepare_socket_activation_environment (string_vector *env)
+prepare_socket_activation_environment (string_vector *env,
+ const struct sact_var *sact_var,
+ size_t num_vars)
{
- char *p;
+ const struct sact_var *var_end;
+ char *new_var;
+ const struct sact_var *var;
size_t i;
*env = (string_vector)empty_vector;
- /* Reserve slots env[0] and env[1]. */
- p = strdup ("LISTEN_PID=xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
- if (p == NULL)
- goto err;
- if (string_vector_append (env, p) == -1) {
- free (p);
- goto err;
- }
- p = strdup ("LISTEN_FDS=1");
- if (p == NULL)
- goto err;
- if (string_vector_append (env, p) == -1) {
- free (p);
- goto err;
+ /* Set the exclusive limit for loops over "sact_var". */
+ var_end = sact_var + num_vars;
+
+ /* New environment variable being constructed for "env". */
+ new_var = NULL;
+
+ /* Copy "sact_var" to the front of "env". */
+ for (var = sact_var; var < var_end; ++var) {
+ size_t new_var_size;
+ char *p;
+
+ /* Calculate the size of the "NAME=value" string. */
+ if (ADD_OVERFLOW (var->prefix_len, var->value_len, &new_var_size) ||
+ ADD_OVERFLOW (new_var_size, 1u, &new_var_size)) {
+ errno = EOVERFLOW;
+ goto err;
+ }
+
+ /* Allocate and format "NAME=value". */
+ new_var = malloc (new_var_size);
+ if (new_var == NULL)
+ goto err;
+ p = new_var;
+
+ memcpy (p, var->prefix, var->prefix_len);
+ p += var->prefix_len;
+
+ memcpy (p, var->value, var->value_len);
+ p += var->value_len;
+
+ *p++ = '\0';
+
+ /* Push "NAME=value" to the vector. */
+ if (string_vector_append (env, new_var) == -1)
+ goto err;
+ /* Ownership transferred. */
+ new_var = NULL;
}
- /* Append the current environment, but remove LISTEN_PID, LISTEN_FDS. */
+ /* Append the current environment to "env", but remove "sact_var". */
for (i = 0; environ[i] != NULL; ++i) {
- if (strncmp (environ[i], "LISTEN_PID=", PREFIX_LENGTH) != 0 &&
- strncmp (environ[i], "LISTEN_FDS=", PREFIX_LENGTH) != 0) {
- char *copy = strdup (environ[i]);
- if (copy == NULL)
- goto err;
- if (string_vector_append (env, copy) == -1) {
- free (copy);
- goto err;
- }
+ for (var = sact_var; var < var_end; ++var) {
+ if (strncmp (environ[i], var->prefix, var->prefix_len) == 0)
+ break;
}
+ /* Drop known socket activation variable from the current environment. */
+ if (var < var_end)
+ continue;
+
+ new_var = strdup (environ[i]);
+ if (new_var == NULL)
+ goto err;
+
+ if (string_vector_append (env, new_var) == -1)
+ goto err;
+ /* Ownership transferred. */
+ new_var = NULL;
}
/* The environ must be NULL-terminated. */
if (string_vector_append (env, NULL) == -1)
goto err;
return 0;
err:
set_error (errno, "malloc");
+ free (new_var);
string_vector_empty (env);
return -1;
}
STATE_MACHINE {
CONNECT_SA.START:
enum state next;
char *tmpdir;
char *sockpath;
int s;
struct sockaddr_un addr;
struct execvpe execvpe_ctx;
+ size_t num_vars;
+ struct sact_var sact_var[2];
+ size_t pid_ofs;
string_vector env;
pid_t pid;
assert (!h->sock);
assert (h->argv.ptr);
assert (h->argv.ptr[0]);
@@ -153,13 +237,18 @@ CONNECT_SA.START:
if (nbd_internal_execvpe_init (&execvpe_ctx, h->argv.ptr[0], h->argv.len) ==
-1) {
set_error (errno, "nbd_internal_execvpe_init");
goto unlink_sockpath;
}
- if (prepare_socket_activation_environment (&env) == -1)
+ num_vars = 0;
+ SACT_VAR_PUSH (sact_var, &num_vars,
+ "LISTEN_PID=", "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", &pid_ofs);
+ SACT_VAR_PUSH (sact_var, &num_vars,
+ "LISTEN_FDS=", "1", NULL);
+ if (prepare_socket_activation_environment (&env, sact_var, num_vars) == -1)
/* prepare_socket_activation_environment() calls set_error() internally */
goto uninit_execvpe;
pid = fork ();
if (pid == -1) {
set_error (errno, "fork");
@@ -193,13 +282,14 @@ CONNECT_SA.START:
}
}
char buf[32];
const char *v =
nbd_internal_fork_safe_itoa ((long) getpid (), buf, sizeof buf);
- strcpy (&env.ptr[0][PREFIX_LENGTH], v);
+ NBD_INTERNAL_FORK_SAFE_ASSERT (strlen (v) <= sact_var[pid_ofs].value_len);
+ strcpy (env.ptr[pid_ofs] + sact_var[pid_ofs].prefix_len, v);
/* Restore SIGPIPE back to SIG_DFL. */
if (signal (SIGPIPE, SIG_DFL) == SIG_ERR) {
nbd_internal_fork_safe_perror ("signal");
_exit (126);
}
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