From 77dfab7bd3d8e503d3ba196480f3ffa96bedcd48 Mon Sep 17 00:00:00 2001 From: Eric Wong Date: Sun, 26 Nov 2023 20:07:45 +0000 Subject: xap_helper: avoid strerror(3) inside signal handler It's not async-signal-safe and the glibc implementation uses malloc via asnprintf. Practically it's not a problem unless the kernel OOMs and the write(2) fails to the self-pipe. --- lib/PublicInbox/xap_helper.h | 29 ++++++++++++----------------- 1 file changed, 12 insertions(+), 17 deletions(-) (limited to 'lib/PublicInbox') diff --git a/lib/PublicInbox/xap_helper.h b/lib/PublicInbox/xap_helper.h index b6b517d5..1d8437c9 100644 --- a/lib/PublicInbox/xap_helper.h +++ b/lib/PublicInbox/xap_helper.h @@ -980,7 +980,8 @@ static void sigp(int sig) // parent signal handler { static const char eagain[] = "signals coming in too fast"; static const char bad_sig[] = "BUG: bad sig\n"; - static const char write_err[] = "BUG: sigp write: "; + static const char write_errno[] = "BUG: sigp write (errno)"; + static const char write_zero[] = "BUG: sigp write wrote zero bytes"; char c = 0; switch (sig) { @@ -992,23 +993,17 @@ static void sigp(int sig) // parent signal handler _exit(EXIT_FAILURE); } ssize_t w = write(pipefds[1], &c, 1); - if (w == sizeof(c)) return; - int e = 0; - if (w < 0) { - e = errno; - if (e == EAGAIN) { - write(STDERR_FILENO, eagain, sizeof(eagain) - 1); - return; - } + if (w > 0) return; + if (w < 0 && errno == EAGAIN) { + write(STDERR_FILENO, eagain, sizeof(eagain) - 1); + return; + } else if (w == 0) { + write(STDERR_FILENO, write_zero, sizeof(write_zero) - 1); + } else { + // strerror isn't technically async-signal-safe, and + // strerrordesc_np+strerrorname_np isn't portable + write(STDERR_FILENO, write_errno, sizeof(write_errno) - 1); } - struct iovec iov[3]; - iov[0].iov_base = (void *)write_err; - iov[0].iov_len = sizeof(write_err) - 1; - iov[1].iov_base = (void *)(e ? strerror(e) : "zero write"); - iov[1].iov_len = strlen((const char *)iov[1].iov_base); - iov[2].iov_base = (void *)"\n"; - iov[2].iov_len = 1; - (void)writev(STDERR_FILENO, iov, MY_ARRAY_SIZE(iov)); _exit(EXIT_FAILURE); } -- cgit v1.2.3-24-ge0c7