git/pager.c
Enzo Matsumiya f917f57f40 pager: fix crash when pager program doesn't exist
When prepare_cmd() fails for, e.g., pager process setup,
child_process_clear() frees the memory in pager_process.args, but .argv
was pointed to pager_process.args.v earlier in start_command(), so it's
now a dangling pointer.

setup_pager() is then called a second time, from cmd_log_init_finish()
in this case, and any further operations using its .argv, e.g. strvec_*,
will use the dangling pointer and eventually crash. According to trivial
tests, setup_pager() is not called twice if the first call is
successful.

This patch makes sure that pager_process is properly initialized on
setup_pager(). Drop CHILD_PROCESS_INIT from its declaration since it's
no longer really necessary.

Add a test to catch possible regressions.

Reproducer:
$ git config pager.show INVALID_PAGER
$ git show $VALID_COMMIT
error: cannot run INVALID_PAGER: No such file or directory
[1]    3619 segmentation fault (core dumped)  git show $VALID_COMMIT

Signed-off-by: Enzo Matsumiya <ematsumiya@suse.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-11-24 16:14:10 -08:00

259 lines
5.3 KiB
C

#include "cache.h"
#include "config.h"
#include "run-command.h"
#include "sigchain.h"
#include "alias.h"
#ifndef DEFAULT_PAGER
#define DEFAULT_PAGER "less"
#endif
static struct child_process pager_process;
static const char *pager_program;
/* Is the value coming back from term_columns() just a guess? */
static int term_columns_guessed;
static void close_pager_fds(void)
{
/* signal EOF to pager */
close(1);
close(2);
}
static void wait_for_pager_atexit(void)
{
fflush(stdout);
fflush(stderr);
close_pager_fds();
finish_command(&pager_process);
}
static void wait_for_pager_signal(int signo)
{
close_pager_fds();
finish_command_in_signal(&pager_process);
sigchain_pop(signo);
raise(signo);
}
static int core_pager_config(const char *var, const char *value, void *data)
{
if (!strcmp(var, "core.pager"))
return git_config_string(&pager_program, var, value);
return 0;
}
const char *git_pager(int stdout_is_tty)
{
const char *pager;
if (!stdout_is_tty)
return NULL;
pager = getenv("GIT_PAGER");
if (!pager) {
if (!pager_program)
read_early_config(core_pager_config, NULL);
pager = pager_program;
}
if (!pager)
pager = getenv("PAGER");
if (!pager)
pager = DEFAULT_PAGER;
if (!*pager || !strcmp(pager, "cat"))
pager = NULL;
return pager;
}
static void setup_pager_env(struct strvec *env)
{
const char **argv;
int i;
char *pager_env = xstrdup(PAGER_ENV);
int n = split_cmdline(pager_env, &argv);
if (n < 0)
die("malformed build-time PAGER_ENV: %s",
split_cmdline_strerror(n));
for (i = 0; i < n; i++) {
char *cp = strchr(argv[i], '=');
if (!cp)
die("malformed build-time PAGER_ENV");
*cp = '\0';
if (!getenv(argv[i])) {
*cp = '=';
strvec_push(env, argv[i]);
}
}
free(pager_env);
free(argv);
}
void prepare_pager_args(struct child_process *pager_process, const char *pager)
{
strvec_push(&pager_process->args, pager);
pager_process->use_shell = 1;
setup_pager_env(&pager_process->env_array);
pager_process->trace2_child_class = "pager";
}
void setup_pager(void)
{
const char *pager = git_pager(isatty(1));
if (!pager)
return;
/*
* After we redirect standard output, we won't be able to use an ioctl
* to get the terminal size. Let's grab it now, and then set $COLUMNS
* to communicate it to any sub-processes.
*/
{
char buf[64];
xsnprintf(buf, sizeof(buf), "%d", term_columns());
if (!term_columns_guessed)
setenv("COLUMNS", buf, 0);
}
setenv("GIT_PAGER_IN_USE", "true", 1);
child_process_init(&pager_process);
/* spawn the pager */
prepare_pager_args(&pager_process, pager);
pager_process.in = -1;
strvec_push(&pager_process.env_array, "GIT_PAGER_IN_USE");
if (start_command(&pager_process))
return;
/* original process continues, but writes to the pipe */
dup2(pager_process.in, 1);
if (isatty(2))
dup2(pager_process.in, 2);
close(pager_process.in);
/* this makes sure that the parent terminates after the pager */
sigchain_push_common(wait_for_pager_signal);
atexit(wait_for_pager_atexit);
}
int pager_in_use(void)
{
return git_env_bool("GIT_PAGER_IN_USE", 0);
}
/*
* Return cached value (if set) or $COLUMNS environment variable (if
* set and positive) or ioctl(1, TIOCGWINSZ).ws_col (if positive),
* and default to 80 if all else fails.
*/
int term_columns(void)
{
static int term_columns_at_startup;
char *col_string;
int n_cols;
if (term_columns_at_startup)
return term_columns_at_startup;
term_columns_at_startup = 80;
term_columns_guessed = 1;
col_string = getenv("COLUMNS");
if (col_string && (n_cols = atoi(col_string)) > 0) {
term_columns_at_startup = n_cols;
term_columns_guessed = 0;
}
#ifdef TIOCGWINSZ
else {
struct winsize ws;
if (!ioctl(1, TIOCGWINSZ, &ws) && ws.ws_col) {
term_columns_at_startup = ws.ws_col;
term_columns_guessed = 0;
}
}
#endif
return term_columns_at_startup;
}
/*
* Clear the entire line, leave cursor in first column.
*/
void term_clear_line(void)
{
if (is_terminal_dumb())
/*
* Fall back to print a terminal width worth of space
* characters (hoping that the terminal is still as wide
* as it was upon the first call to term_columns()).
*/
fprintf(stderr, "\r%*s\r", term_columns(), "");
else
/*
* On non-dumb terminals use an escape sequence to clear
* the whole line, no matter how wide the terminal.
*/
fputs("\r\033[K", stderr);
}
/*
* How many columns do we need to show this number in decimal?
*/
int decimal_width(uintmax_t number)
{
int width;
for (width = 1; number >= 10; width++)
number /= 10;
return width;
}
struct pager_command_config_data {
const char *cmd;
int want;
char *value;
};
static int pager_command_config(const char *var, const char *value, void *vdata)
{
struct pager_command_config_data *data = vdata;
const char *cmd;
if (skip_prefix(var, "pager.", &cmd) && !strcmp(cmd, data->cmd)) {
int b = git_parse_maybe_bool(value);
if (b >= 0)
data->want = b;
else {
data->want = 1;
data->value = xstrdup(value);
}
}
return 0;
}
/* returns 0 for "no pager", 1 for "use pager", and -1 for "not specified" */
int check_pager_config(const char *cmd)
{
struct pager_command_config_data data;
data.cmd = cmd;
data.want = -1;
data.value = NULL;
read_early_config(pager_command_config, &data);
if (data.value)
pager_program = data.value;
return data.want;
}