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From 60f868ac16c4678d60f17d62fa3b47534d4d07cb Mon Sep 17 00:00:00 2001
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From: Jakub Hrozek <jhrozek@redhat.com>
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Date: Mon, 28 May 2018 21:41:49 +0200
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Subject: [PATCH] SSH: Do not exit abruptly if SSHD closes its end of the pipe
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before reading all the SSH keys
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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Resolves:
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https://pagure.io/SSSD/sssd/issue/3747
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Before writing the keys to sshd, ignore SIGPIPE so that if the pipe
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towards the authorizedkeys helper is closed, the sss_ssh_authorizedkeys
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helper is not terminated with SIGPIPE, but instead proceeds and then the
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write(2) calls would non-terminally fail with EPIPE.
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Reviewed-by: Fabiano Fidêncio <fidencio@redhat.com>
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(cherry picked from commit cb138d7d060611e891d341db08477e41f9a3d17d)
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---
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src/sss_client/ssh/sss_ssh_authorizedkeys.c | 35 ++++++++++++++++++++-
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1 file changed, 34 insertions(+), 1 deletion(-)
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diff --git a/src/sss_client/ssh/sss_ssh_authorizedkeys.c b/src/sss_client/ssh/sss_ssh_authorizedkeys.c
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index 782a9f44379bff5346c896b3e03570720632c0be..b0280fbf8b0ed0501d792973241b826fc4a7a04d 100644
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--- a/src/sss_client/ssh/sss_ssh_authorizedkeys.c
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+++ b/src/sss_client/ssh/sss_ssh_authorizedkeys.c
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@@ -21,6 +21,7 @@
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#include <stdio.h>
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#include <talloc.h>
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#include <popt.h>
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+#include <signal.h>
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#include "util/util.h"
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#include "util/crypto/sss_crypto.h"
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@@ -99,8 +100,16 @@ int main(int argc, const char **argv)
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goto fini;
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}
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+ /* if sshd closes its end of the pipe, we don't want sss_ssh_authorizedkeys
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+ * to exit abruptly, but to finish gracefully instead because the valid
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+ * key can be present in the data already written
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+ */
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+ signal(SIGPIPE, SIG_IGN);
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+
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/* print results */
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for (i = 0; i < ent->num_pubkeys; i++) {
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+ char *repr_break = NULL;
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+
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ret = sss_ssh_format_pubkey(mem_ctx, &ent->pubkeys[i], &repr);
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if (ret != EOK) {
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DEBUG(SSSDBG_OP_FAILURE,
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@@ -109,7 +118,31 @@ int main(int argc, const char **argv)
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continue;
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}
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- printf("%s\n", repr);
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+ /* OpenSSH expects a linebreak after each key */
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+ repr_break = talloc_asprintf(mem_ctx, "%s\n", repr);
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+ talloc_zfree(repr);
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+ if (repr_break == NULL) {
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+ ret = ENOMEM;
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+ goto fini;
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+ }
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+
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+ ret = sss_atomic_write_s(STDOUT_FILENO, repr_break, strlen(repr_break));
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+ /* Avoid spiking memory with too many large keys */
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+ talloc_zfree(repr_break);
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+ if (ret < 0) {
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+ ret = errno;
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+ if (ret == EPIPE) {
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+ DEBUG(SSSDBG_MINOR_FAILURE,
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+ "SSHD closed the pipe before all keys could be written\n");
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+ /* Return 0 so that openssh doesn't abort pubkey auth */
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+ ret = 0;
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+ goto fini;
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+ }
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+ DEBUG(SSSDBG_CRIT_FAILURE,
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+ "sss_atomic_write_s() failed (%d): %s\n",
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+ ret, strerror(ret));
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+ goto fini;
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+ }
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}
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ret = EXIT_SUCCESS;
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--
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2.17.1
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