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posix_spawn - implement support for POSIX_SPAWN_CLOEXEC_DEFAULT

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This new posix_spawn attribute flag marks all file descriptors
(except stdin/out/err) as close-on-exec before executing any user
registered file actions (posix_spawn_file_actions_addopen/adddup2).

Test: TreeHugger
Bug: 229913920
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: If458100d6a253a9b0348d4e93a9a610225f89615
This commit is contained in:
Maciej Żenczykowski 2022-01-20 14:56:20 -08:00
parent 3e25f8272f
commit 262b873dea
2 changed files with 27 additions and 1 deletions
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26
libc/bionic/spawn.cpp
View file

@ -33,6 +33,7 @@
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <sys/resource.h>
#include <unistd.h>
#include <android/fdsan.h>
@ -40,6 +41,25 @@
#include "private/ScopedSignalBlocker.h"
#include "private/SigSetConverter.h"
static int set_cloexec(int i) {
int v = fcntl(i, F_GETFD);
if (v == -1) return -1; // almost certainly: errno == EBADF
return fcntl(i, F_SETFD, v | FD_CLOEXEC);
}
// mark all open fds except stdin/out/err as close-on-exec
static int cloexec_except_stdioe() {
// unfortunately getrlimit can lie:
// - both soft and hard limits can be lowered to 0, with fds still open, so it can underestimate
// - in practice it usually is some really large value (like 32K or more)
// even though only a handful of small fds are actually open (ie. < 500),
// this results in poor performance when trying to act on all possibly open fds
struct rlimit m;
int max = getrlimit(RLIMIT_NOFILE, &m) ? 1000000 : m.rlim_max;
for (int i = 3; i < max; ++i) set_cloexec(i);
return 0;
}
enum Action {
kOpen,
kClose,
@ -141,6 +161,10 @@ static void ApplyAttrs(short flags, const posix_spawnattr_t* attr) {
if ((flags & POSIX_SPAWN_SETSIGMASK) != 0) {
if (sigprocmask64(SIG_SETMASK, &(*attr)->sigmask.sigset64, nullptr)) _exit(127);
}
if ((flags & POSIX_SPAWN_CLOEXEC_DEFAULT) != 0) {
if (cloexec_except_stdioe()) _exit(127);
}
}
static int posix_spawn(pid_t* pid_ptr,
@ -199,7 +223,7 @@ int posix_spawnattr_destroy(posix_spawnattr_t* attr) {
int posix_spawnattr_setflags(posix_spawnattr_t* attr, short flags) {
if ((flags & ~(POSIX_SPAWN_RESETIDS | POSIX_SPAWN_SETPGROUP | POSIX_SPAWN_SETSIGDEF |
POSIX_SPAWN_SETSIGMASK | POSIX_SPAWN_SETSCHEDPARAM | POSIX_SPAWN_SETSCHEDULER |
POSIX_SPAWN_USEVFORK | POSIX_SPAWN_SETSID)) != 0) {
POSIX_SPAWN_USEVFORK | POSIX_SPAWN_SETSID | POSIX_SPAWN_CLOEXEC_DEFAULT)) != 0) {
return EINVAL;
}
(*attr)->flags = flags;

2
libc/include/spawn.h
View file

@ -46,6 +46,8 @@ __BEGIN_DECLS
#define POSIX_SPAWN_USEVFORK 64
#define POSIX_SPAWN_SETSID 128
#endif
// mark all fds (except stdin/out/err) as close-on-exec prior to executing registered file actions
#define POSIX_SPAWN_CLOEXEC_DEFAULT 256
typedef struct __posix_spawnattr* posix_spawnattr_t;
typedef struct __posix_spawn_file_actions* posix_spawn_file_actions_t;