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From b6f73810a2e7afd02a231e2dfa14b05752c83db7 Mon Sep 17 00:00:00 2001
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From: "Dmitry V. Levin" <ldv@altlinux.org>
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Date: Wed, 26 Feb 2020 19:20:58 +0000
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Subject: [PATCH] pam_modutil_sanitize_helper_fds: fix SIGPIPE effect of
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PAM_MODUTIL_PIPE_FD
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When pam_modutil_sanitize_helper_fds() is invoked with
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PAM_MODUTIL_PIPE_FD to provide a dummy pipe descriptor for stdout
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or stderr, it closes the read end of the newly created dummy pipe.
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The negative side effect of this approach is that any write to such
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descriptor triggers a SIGPIPE. Avoid this by closing the write end of
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the dummy pipe and using its read end as a dummy pipe descriptor for
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output. Any read from such descriptor returns 0, and any write just
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fails with EBADF, which should work better with unprepared writers.
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* libpam/pam_modutil_sanitize.c (redirect_out_pipe): Remove.
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(redirect_out): Call redirect_in_pipe instead of redirect_out_pipe.
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Fixes: b0ec5d1e ("Introduce pam_modutil_sanitize_helper_fds")
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---
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libpam/pam_modutil_sanitize.c | 30 +-----------------------------
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1 file changed, 1 insertion(+), 29 deletions(-)
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diff --git a/libpam/pam_modutil_sanitize.c b/libpam/pam_modutil_sanitize.c
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index 605c859d..58b9537c 100644
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--- a/libpam/pam_modutil_sanitize.c
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+++ b/libpam/pam_modutil_sanitize.c
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@@ -46,34 +46,6 @@ redirect_in_pipe(pam_handle_t *pamh, int fd, const char *name)
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return fd;
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}
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-/*
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- * Creates a pipe, closes its read end, redirects fd to its write end.
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- * Returns fd on success, -1 otherwise.
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- */
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-static int
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-redirect_out_pipe(pam_handle_t *pamh, int fd, const char *name)
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-{
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- int out[2];
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-
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- if (pipe(out) < 0) {
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- pam_syslog(pamh, LOG_ERR, "Could not create pipe: %m");
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- return -1;
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- }
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-
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- close(out[0]);
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-
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- if (out[1] == fd)
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- return fd;
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-
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- if (dup2(out[1], fd) != fd) {
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- pam_syslog(pamh, LOG_ERR, "dup2 of %s failed: %m", name);
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- fd = -1;
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- }
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-
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- close(out[1]);
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- return fd;
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-}
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-
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/*
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* Opens /dev/null for writing, redirects fd there.
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* Returns fd on success, -1 otherwise.
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@@ -106,7 +78,7 @@ redirect_out(pam_handle_t *pamh, enum pam_modutil_redirect_fd mode,
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{
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switch (mode) {
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case PAM_MODUTIL_PIPE_FD:
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- if (redirect_out_pipe(pamh, fd, name) < 0)
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+ if (redirect_in_pipe(pamh, fd, name) < 0)
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return -1;
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break;
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case PAM_MODUTIL_NULL_FD:
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--
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2.25.3
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