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From adb4360c40df99238c17c3ecedcb1d32d76e2b2e Mon Sep 17 00:00:00 2001
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From: "Todd C. Miller" <Todd.Miller@sudo.ws>
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Date: Fri, 17 Apr 2020 19:08:56 -0600
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Subject: [PATCH] Extend the original file before to the new size before
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updating it. Instead of opening the original file for writing w/ tuncation,
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we first extend the file with zeroes (by writing, not seeking), then
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overwrite it. This should allow sudo to fail early if the disk is out of
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space before it overwrites the original file.
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---
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src/sudo_edit.c | 93 ++++++++++++++++++++++++++++++++++++++++---------
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1 file changed, 77 insertions(+), 16 deletions(-)
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diff --git a/src/sudo_edit.c b/src/sudo_edit.c
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index 28f6c6100..d99a5658a 100644
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--- a/src/sudo_edit.c
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+++ b/src/sudo_edit.c
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@@ -1,7 +1,7 @@
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/*
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* SPDX-License-Identifier: ISC
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*
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- * Copyright (c) 2004-2008, 2010-2018 Todd C. Miller <Todd.Miller@sudo.ws>
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+ * Copyright (c) 2004-2008, 2010-2020 Todd C. Miller <Todd.Miller@sudo.ws>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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@@ -650,6 +650,51 @@ sudo_edit_create_tfiles(struct command_details *command_details,
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debug_return_int(j);
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}
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+/*
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+ * Extend the given fd to the specified size in bytes.
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+ * We do this to allocate disk space up-front before overwriting
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+ * the original file with the temporary. Otherwise, we could
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+ * we run out of disk space after truncating the original file.
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+ */
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+static int
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+sudo_edit_extend_file(int fd, off_t new_size)
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+{
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+ off_t old_size, size;
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+ ssize_t nwritten;
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+ char zeroes[1024] = { '\0' };
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+ debug_decl(sudo_edit_extend_file, SUDO_DEBUG_EDIT);
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+
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+ if ((old_size = lseek(fd, 0, SEEK_END)) == -1) {
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+ sudo_warn("lseek");
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+ debug_return_int(-1);
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+ }
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+ sudo_debug_printf(SUDO_DEBUG_INFO, "%s: extending file from %lld to %lld",
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+ __func__, (long long)old_size, (long long)new_size);
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+
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+ for (size = old_size; size < new_size; size += nwritten) {
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+ size_t len = new_size - size;
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+ if (len > sizeof(zeroes))
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+ len = sizeof(zeroes);
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+ nwritten = write(fd, zeroes, len);
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+ if (nwritten == -1) {
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+ int serrno = errno;
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+ if (ftruncate(fd, old_size) == -1) {
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+ sudo_debug_printf(
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+ SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO|SUDO_DEBUG_ERRNO,
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+ "unable to truncate to %lld", (long long)old_size);
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+ }
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+ errno = serrno;
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+ debug_return_int(-1);
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+ }
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+ }
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+ if (lseek(fd, 0, SEEK_SET) == -1) {
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+ sudo_warn("lseek");
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+ debug_return_int(-1);
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+ }
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+
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+ debug_return_int(0);
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+}
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+
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/*
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* Copy the temporary files specified in tf to the originals.
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* Returns the number of copy errors or 0 if completely successful.
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@@ -708,38 +753,53 @@ sudo_edit_copy_tfiles(struct command_details *command_details,
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switch_user(command_details->euid, command_details->egid,
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command_details->ngroups, command_details->groups);
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oldmask = umask(command_details->umask);
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- ofd = sudo_edit_open(tf[i].ofile, O_WRONLY|O_TRUNC|O_CREAT,
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+ ofd = sudo_edit_open(tf[i].ofile, O_WRONLY|O_CREAT,
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S_IRUSR|S_IWUSR|S_IRGRP|S_IROTH, command_details);
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umask(oldmask);
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switch_user(ROOT_UID, user_details.egid,
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user_details.ngroups, user_details.groups);
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- if (ofd == -1) {
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- sudo_warn(U_("unable to write to %s"), tf[i].ofile);
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- sudo_warnx(U_("contents of edit session left in %s"), tf[i].tfile);
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- close(tfd);
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- errors++;
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- continue;
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+ if (ofd == -1)
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+ goto write_error;
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+ /* Extend the file to the new size if larger before copying. */
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+ if (tf[i].osize > 0 && sb.st_size > tf[i].osize) {
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+ if (sudo_edit_extend_file(ofd, sb.st_size) == -1)
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+ goto write_error;
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}
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+ /* Overwrite the old file with the new contents. */
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while ((nread = read(tfd, buf, sizeof(buf))) > 0) {
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- if ((nwritten = write(ofd, buf, nread)) != nread) {
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+ ssize_t off = 0;
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+ do {
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+ nwritten = write(ofd, buf + off, nread - off);
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if (nwritten == -1)
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- sudo_warn("%s", tf[i].ofile);
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- else
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- sudo_warnx(U_("%s: short write"), tf[i].ofile);
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- break;
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- }
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+ goto write_error;
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+ off += nwritten;
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+ } while (nread > off);
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}
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if (nread == 0) {
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- /* success, got EOF */
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+ /* success, read to EOF */
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+ if (tf[i].osize > 0 && sb.st_size < tf[i].osize) {
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+ /* We don't open with O_TRUNC so must truncate manually. */
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+ if (ftruncate(ofd, sb.st_size) == -1) {
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+ sudo_debug_printf(
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+ SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO|SUDO_DEBUG_ERRNO,
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+ "unable to truncate %s to %lld", tf[i].ofile,
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+ (long long)sb.st_size);
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+ goto write_error;
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+ }
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+ }
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unlink(tf[i].tfile);
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} else if (nread < 0) {
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sudo_warn(U_("unable to read temporary file"));
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sudo_warnx(U_("contents of edit session left in %s"), tf[i].tfile);
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+ errors++;
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} else {
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+write_error:
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sudo_warn(U_("unable to write to %s"), tf[i].ofile);
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sudo_warnx(U_("contents of edit session left in %s"), tf[i].tfile);
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+ errors++;
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}
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- close(ofd);
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+ if (ofd != -1)
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+ close(ofd);
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close(tfd);
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}
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debug_return_int(errors);
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@@ -1065,6 +1125,7 @@ cleanup:
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for (i = 0; i < nfiles; i++) {
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if (tf[i].tfile != NULL)
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unlink(tf[i].tfile);
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+ free(tf[i].tfile);
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}
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}
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free(tf);
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--
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2.26.2
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