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Change vfork calls to use vfork_and_run operation with GNO-compatible semantics

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This commit is contained in:
Stephen Heumann 2014-10-27 13:06:24 -05:00
parent e61b4040ec
commit 16c89af688
4 changed files with 200 additions and 119 deletions
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3
build
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@ -52,4 +52,5 @@ libbb/parse_mode.c \
libbb/messages.c \
libbb/appletlib.c \
libbb/get_last_path_component.c \
libbb/mempcpy.c
libbb/mempcpy.c \
libbb/vfork_and_run.c

4
include/libbb.h
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@ -1035,6 +1035,10 @@ void bb_sanitize_stdio(void) FAST_FUNC;
int sanitize_env_if_suid(void) FAST_FUNC;
pid_t vfork_and_run(void (*fn)(void*) NORETURN, void *arg);
pid_t xvfork_and_run(void (*fn)(void*) NORETURN, void *arg);
char* single_argv(char **argv) FAST_FUNC;
extern const char *const bb_argv_dash[]; /* "-", NULL */
extern const char *opt_complementary;

24
libbb/vfork_and_run.c Normal file
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@ -0,0 +1,24 @@
#include <unistd.h>
#include "libbb.h"
/* Like vfork, but calls fn(arg) in the child instead of returning.
* This is designed to match the semantics of GNO's fork2 call.
*/
pid_t vfork_and_run(void (*fn)(void*) NORETURN, void *arg) {
pid_t pid = vfork();
if (pid == 0) {
fn(arg);
}
return pid;
}
pid_t xvfork_and_run(void (*fn)(void*) NORETURN, void *arg) {
pid_t pid = vfork_and_run(fn, arg);
if (pid < 0)
bb_perror_msg_and_die("vfork");
return pid;
}

288
shell/hush.c
View File

@ -5827,6 +5827,13 @@ static void parse_and_run_file(FILE *f)
}
#if ENABLE_HUSH_TICK
static void xforked_child(void *) NORETURN;
struct child_args2 {
int *channel;
const char *s;
char ***to_free_p;
};
static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
{
pid_t pid;
@ -5836,82 +5843,18 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
# endif
xpipe(channel);
pid = BB_MMU ? xfork() : xvfork();
struct child_args2 args_struct = {
channel,
s,
&to_free,
};
pid = BB_MMU ? xfork() : xvfork_and_run(xforked_child, &args_struct);
#if BB_MMU
if (pid == 0) { /* child */
disable_restore_tty_pgrp_on_exit();
/* Process substitution is not considered to be usual
* 'command execution'.
* SUSv3 says ctrl-Z should be ignored, ctrl-C should not.
*/
bb_signals(0
+ (1 << SIGTSTP)
+ (1 << SIGTTIN)
+ (1 << SIGTTOU)
, SIG_IGN);
CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */
close(channel[0]); /* NB: close _first_, then move fd! */
xmove_fd(channel[1], 1);
/* Prevent it from trying to handle ctrl-z etc */
IF_HUSH_JOB(G.run_list_level = 1;)
/* Awful hack for `trap` or $(trap).
*
* http://www.opengroup.org/onlinepubs/009695399/utilities/trap.html
* contains an example where "trap" is executed in a subshell:
*
* save_traps=$(trap)
* ...
* eval "$save_traps"
*
* Standard does not say that "trap" in subshell shall print
* parent shell's traps. It only says that its output
* must have suitable form, but then, in the above example
* (which is not supposed to be normative), it implies that.
*
* bash (and probably other shell) does implement it
* (traps are reset to defaults, but "trap" still shows them),
* but as a result, "trap" logic is hopelessly messed up:
*
* # trap
* trap -- 'echo Ho' SIGWINCH <--- we have a handler
* # (trap) <--- trap is in subshell - no output (correct, traps are reset)
* # true | trap <--- trap is in subshell - no output (ditto)
* # echo `true | trap` <--- in subshell - output (but traps are reset!)
* trap -- 'echo Ho' SIGWINCH
* # echo `(trap)` <--- in subshell in subshell - output
* trap -- 'echo Ho' SIGWINCH
* # echo `true | (trap)` <--- in subshell in subshell in subshell - output!
* trap -- 'echo Ho' SIGWINCH
*
* The rules when to forget and when to not forget traps
* get really complex and nonsensical.
*
* Our solution: ONLY bare $(trap) or `trap` is special.
*/
s = skip_whitespace(s);
if (strncmp(s, "trap", 4) == 0
&& skip_whitespace(s + 4)[0] == '\0'
) {
static const char *const argv[] = { NULL, NULL };
builtin_trap((char**)argv);
exit(0); /* not _exit() - we need to fflush */
}
# if BB_MMU
reset_traps_to_defaults();
parse_and_run_string(s);
_exit(G.last_exitcode);
# else
/* We re-execute after vfork on NOMMU. This makes this script safe:
* yes "0123456789012345678901234567890" | dd bs=32 count=64k >BIG
* huge=`cat BIG` # was blocking here forever
* echo OK
*/
re_execute_shell(&to_free,
s,
G.global_argv[0],
G.global_argv + 1,
NULL);
# endif
xforked_child(&args_struct);
}
#endif
/* parent */
*pid_p = pid;
@ -5930,6 +5873,85 @@ static FILE *generate_stream_from_string(const char *s, pid_t *pid_p)
return xfdopen_for_read(channel[0]);
}
static void xforked_child(void *args_struct) {
struct child_args2 *args = (struct child_args2 *)args_struct;
disable_restore_tty_pgrp_on_exit();
/* Process substitution is not considered to be usual
* 'command execution'.
* SUSv3 says ctrl-Z should be ignored, ctrl-C should not.
*/
bb_signals(0
+ (1 << SIGTSTP)
+ (1 << SIGTTIN)
+ (1 << SIGTTOU)
, SIG_IGN);
CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */
close(args->channel[0]); /* NB: close _first_, then move fd! */
xmove_fd(args->channel[1], 1);
/* Prevent it from trying to handle ctrl-z etc */
IF_HUSH_JOB(G.run_list_level = 1;)
/* Awful hack for `trap` or $(trap).
*
* http://www.opengroup.org/onlinepubs/009695399/utilities/trap.html
* contains an example where "trap" is executed in a subshell:
*
* save_traps=$(trap)
* ...
* eval "$save_traps"
*
* Standard does not say that "trap" in subshell shall print
* parent shell's traps. It only says that its output
* must have suitable form, but then, in the above example
* (which is not supposed to be normative), it implies that.
*
* bash (and probably other shell) does implement it
* (traps are reset to defaults, but "trap" still shows them),
* but as a result, "trap" logic is hopelessly messed up:
*
* # trap
* trap -- 'echo Ho' SIGWINCH <--- we have a handler
* # (trap) <--- trap is in subshell - no output (correct, traps are reset)
* # true | trap <--- trap is in subshell - no output (ditto)
* # echo `true | trap` <--- in subshell - output (but traps are reset!)
* trap -- 'echo Ho' SIGWINCH
* # echo `(trap)` <--- in subshell in subshell - output
* trap -- 'echo Ho' SIGWINCH
* # echo `true | (trap)` <--- in subshell in subshell in subshell - output!
* trap -- 'echo Ho' SIGWINCH
*
* The rules when to forget and when to not forget traps
* get really complex and nonsensical.
*
* Our solution: ONLY bare $(trap) or `trap` is special.
*/
args->s = skip_whitespace(args->s);
if (strncmp(args->s, "trap", 4) == 0
&& skip_whitespace(args->s + 4)[0] == '\0'
) {
static const char *const argv[] = { NULL, NULL };
builtin_trap((char**)argv);
exit(0); /* not _exit() - we need to fflush */
}
# if BB_MMU
reset_traps_to_defaults();
parse_and_run_string(s);
_exit(G.last_exitcode);
# else
/* We re-execute after vfork on NOMMU. This makes this script safe:
* yes "0123456789012345678901234567890" | dd bs=32 count=64k >BIG
* huge=`cat BIG` # was blocking here forever
* echo OK
*/
re_execute_shell(args->to_free_p,
args->s,
G.global_argv[0],
G.global_argv + 1,
NULL);
# endif
}
/* Return code is exit status of the process that is run. */
static int process_command_subs(o_string *dest, const char *s)
{
@ -6926,6 +6948,17 @@ static int redirect_and_varexp_helper(char ***new_env_p,
}
return rcode;
}
static void forked_child(void *) NORETURN;
struct child_args {
struct pipe **pi_p;
int *next_infd_p;
struct fd_pair *pipefds_p;
struct command **command_p;
volatile nommu_save_t *nommu_save_p;
char ***argv_expanded_p;
};
static NOINLINE int run_pipe(struct pipe *pi)
{
static const char *const null_ptr = NULL;
@ -7191,52 +7224,21 @@ static NOINLINE int run_pipe(struct pipe *pi)
if (cmd_no < pi->num_cmds)
xpiped_pair(pipefds);
command->pid = BB_MMU ? fork() : vfork();
struct child_args args_struct = {
&pi,
&next_infd,
&pipefds,
&command,
&nommu_save,
&argv_expanded,
};
command->pid = BB_MMU ? fork() : vfork_and_run(forked_child, &args_struct);
#if BB_MMU
if (!command->pid) { /* child */
#if ENABLE_HUSH_JOB
disable_restore_tty_pgrp_on_exit();
CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */
/* Every child adds itself to new process group
* with pgid == pid_of_first_child_in_pipe */
if (G.run_list_level == 1 && G_interactive_fd) {
pid_t pgrp;
pgrp = pi->pgrp;
if (pgrp < 0) /* true for 1st process only */
pgrp = getpid();
if (setpgid(0, pgrp) == 0
&& pi->followup != PIPE_BG
&& G_saved_tty_pgrp /* we have ctty */
) {
/* We do it in *every* child, not just first,
* to avoid races */
tcsetpgrp(G_interactive_fd, pgrp);
}
}
#endif
if (pi->alive_cmds == 0 && pi->followup == PIPE_BG) {
/* 1st cmd in backgrounded pipe
* should have its stdin /dev/null'ed */
close(0);
if (open(bb_dev_null, O_RDONLY))
xopen("/", O_RDONLY);
} else {
xmove_fd(next_infd, 0);
}
xmove_fd(pipefds.wr, 1);
if (pipefds.rd > 1)
close(pipefds.rd);
/* Like bash, explicit redirects override pipes,
* and the pipe fd is available for dup'ing. */
if (setup_redirects(command, NULL))
_exit(1);
/* Stores to nommu_save list of env vars putenv'ed
* (NOMMU, on MMU we don't need that) */
/* cast away volatility... */
pseudo_exec((nommu_save_t*) &nommu_save, command, argv_expanded);
/* pseudo_exec() does not return */
forked_child(&args_struct);
}
#endif
/* parent or error */
#if ENABLE_HUSH_FAST
@ -7283,6 +7285,56 @@ static NOINLINE int run_pipe(struct pipe *pi)
debug_printf_exec("run_pipe return -1 (%u children started)\n", pi->alive_cmds);
return -1;
}
static void forked_child(void *args_struct) {
struct child_args *args = (struct child_args *)args_struct;
#if ENABLE_HUSH_JOB
disable_restore_tty_pgrp_on_exit();
CLEAR_RANDOM_T(&G.random_gen); /* or else $RANDOM repeats in child */
/* Every child adds itself to new process group
* with pgid == pid_of_first_child_in_pipe */
if (G.run_list_level == 1 && G_interactive_fd) {
pid_t pgrp;
pgrp = (*args->pi_p)->pgrp;
if (pgrp < 0) /* true for 1st process only */
pgrp = getpid();
if (setpgid(0, pgrp) == 0
&& (*args->pi_p)->followup != PIPE_BG
&& G_saved_tty_pgrp /* we have ctty */
) {
/* We do it in *every* child, not just first,
* to avoid races */
tcsetpgrp(G_interactive_fd, pgrp);
}
}
#endif
if ((*args->pi_p)->alive_cmds == 0 && (*args->pi_p)->followup == PIPE_BG) {
/* 1st cmd in backgrounded pipe
* should have its stdin /dev/null'ed */
close(0);
if (open(bb_dev_null, O_RDONLY))
xopen("/", O_RDONLY);
} else {
xmove_fd(*args->next_infd_p, 0);
}
xmove_fd(args->pipefds_p->wr, 1);
if (args->pipefds_p->rd > 1)
close(args->pipefds_p->rd);
/* Like bash, explicit redirects override pipes,
* and the pipe fd is available for dup'ing. */
if (setup_redirects(*args->command_p, NULL))
_exit(1);
/* Stores to nommu_save list of env vars putenv'ed
* (NOMMU, on MMU we don't need that) */
/* cast away volatility... */
pseudo_exec((nommu_save_t*) args->nommu_save_p, *args->command_p, *args->argv_expanded_p);
/* pseudo_exec() does not return */
}
/* NB: called by pseudo_exec, and therefore must not modify any
* global data until exec/_exit (we can be a child after vfork!) */