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2207970 - CVE-2023-24805 cups-filters: remote code execution in cups-filters, beh CUPS backend

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Zdenek Dohnal 2023-05-17 15:53:15 +02:00
parent 177ffd57f4
commit d3304142ee
2 changed files with 220 additions and 1 deletions
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215
0001-Merge-pull-request-from-GHSA-gpxc-v2m8-fr3x.patch Normal file
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@ -0,0 +1,215 @@
From 8f274035756c04efeb77eb654e9d4c4447287d65 Mon Sep 17 00:00:00 2001
From: Till Kamppeter <till.kamppeter@gmail.com>
Date: Wed, 17 May 2023 11:12:37 +0200
Subject: [PATCH] Merge pull request from GHSA-gpxc-v2m8-fr3x
* beh backend: Use execv() instead of system() - CVE-2023-24805
With execv() command line arguments are passed as separate strings and
not the full command line in a single string. This prevents arbitrary
command execution by escaping the quoting of the arguments in a job
with forged job title.
* beh backend: Extra checks against odd/forged input - CVE-2023-24805
- Do not allow '/' in the scheme of the URI (= backend executable
name), to assure that only backends inside /usr/lib/cups/backend/
are used.
- Pre-define scheme buffer to empty string, to be defined for case of
uri being NULL.
- URI must have ':', to split off scheme, otherwise error.
- Check return value of snprintf() to create call path for backend, to
error out on truncation of a too long scheme or on complete failure
due to a completely odd scheme.
* beh backend: Further improvements - CVE-2023-24805
- Use strncat() instead of strncpy() for getting scheme from URI, the latter
does not require setting terminating zero byte in case of truncation.
- Also exclude "." or ".." as scheme, as directories are not valid CUPS
backends.
- Do not use fprintf() in sigterm_handler(), to not interfere with a
fprintf() which could be running in the main process when
sigterm_handler() is triggered.
- Use "static volatile int" for global variable job_canceled.
---
backend/beh.c | 109 ++++++++++++++++++++++++++++++++++++++------------
1 file changed, 84 insertions(+), 25 deletions(-)
diff --git a/backend/beh.c b/backend/beh.c
index 7e588c2e3..121e64905 100644
--- a/backend/beh.c
+++ b/backend/beh.c
@@ -26,13 +26,14 @@
#include <signal.h>
#include <string.h>
#include <errno.h>
+#include <sys/wait.h>
//
// Local globals...
//
-static int job_canceled = 0; // Set to 1 on SIGTERM
+static volatile int job_canceled = 0; // Set to 1 on SIGTERM
//
@@ -237,21 +238,44 @@ call_backend(char *uri, // I - URI of final destination
char *filename) // I - File name of input data
{
const char *cups_serverbin; // Location of programs
+ char *backend_argv[8]; // Arguments for called CUPS backend
char scheme[1024], // Scheme from URI
*ptr, // Pointer into scheme
- cmdline[65536]; // Backend command line
- int retval;
+ backend_path[2048]; // Backend path
+ int pid,
+ wait_pid,
+ wait_status,
+ retval = 0;
+ int bytes;
+
//
// Build the backend command line...
//
- strncpy(scheme, uri, sizeof(scheme) - 1);
- if (strlen(uri) > 1023)
- scheme[1023] = '\0';
+ scheme[0] = '\0';
+ strncat(scheme, uri, sizeof(scheme) - 1);
if ((ptr = strchr(scheme, ':')) != NULL)
*ptr = '\0';
-
+ else
+ {
+ fprintf(stderr,
+ "ERROR: beh: Invalid URI, no colon (':') to mark end of scheme part.\n");
+ exit (CUPS_BACKEND_FAILED);
+ }
+ if (strchr(scheme, '/'))
+ {
+ fprintf(stderr,
+ "ERROR: beh: Invalid URI, scheme contains a slash ('/').\n");
+ exit (CUPS_BACKEND_FAILED);
+ }
+ if (!strcmp(scheme, ".") || !strcmp(scheme, ".."))
+ {
+ fprintf(stderr,
+ "ERROR: beh: Invalid URI, scheme (\"%s\") is a directory.\n",
+ scheme);
+ exit (CUPS_BACKEND_FAILED);
+ }
if ((cups_serverbin = getenv("CUPS_SERVERBIN")) == NULL)
cups_serverbin = CUPS_SERVERBIN;
@@ -261,16 +285,25 @@ call_backend(char *uri, // I - URI of final destination
"ERROR: beh: Direct output into a file not supported.\n");
exit (CUPS_BACKEND_FAILED);
}
- else
- snprintf(cmdline, sizeof(cmdline),
- "%s/backend/%s '%s' '%s' '%s' '%s' '%s' %s",
- cups_serverbin, scheme, argv[1], argv[2], argv[3],
- // Apply number of copies only if beh was called with a
- // file name and not with the print data in stdin, as
- // backends should handle copies only if they are called
- // with a file name
- (argc == 6 ? "1" : argv[4]),
- argv[5], filename);
+
+ backend_argv[0] = uri;
+ backend_argv[1] = argv[1];
+ backend_argv[2] = argv[2];
+ backend_argv[3] = argv[3];
+ backend_argv[4] = (argc == 6 ? "1" : argv[4]);
+ backend_argv[5] = argv[5];
+ backend_argv[6] = filename;
+ backend_argv[7] = NULL;
+
+ bytes = snprintf(backend_path, sizeof(backend_path),
+ "%s/backend/%s", cups_serverbin, scheme);
+ if (bytes < 0 || bytes >= sizeof(backend_path))
+ {
+ fprintf(stderr,
+ "ERROR: beh: Invalid scheme (\"%s\"), could not determing backend path.\n",
+ scheme);
+ exit (CUPS_BACKEND_FAILED);
+ }
//
// Overwrite the device URI and run the actual backend...
@@ -279,17 +312,41 @@ call_backend(char *uri, // I - URI of final destination
setenv("DEVICE_URI", uri, 1);
fprintf(stderr,
- "DEBUG: beh: Executing backend command line \"%s\"...\n",
- cmdline);
+ "DEBUG: beh: Executing backend command line \"%s '%s' '%s' '%s' '%s' '%s'%s%s\"...\n",
+ backend_path, backend_argv[1], backend_argv[2], backend_argv[3],
+ backend_argv[4], backend_argv[5],
+ (backend_argv[6] && backend_argv[6][0] ? " " : ""),
+ (backend_argv[6] && backend_argv[6][0] ? backend_argv[6] : ""));
fprintf(stderr,
"DEBUG: beh: Using device URI: %s\n",
uri);
- retval = system(cmdline) >> 8;
+ if ((pid = fork()) == 0)
+ {
+ retval = execv(backend_path, backend_argv);
- if (retval == -1)
- fprintf(stderr, "ERROR: Unable to execute backend command line: %s\n",
- strerror(errno));
+ if (retval == -1)
+ fprintf(stderr, "ERROR: Unable to execute backend: %s\n",
+ strerror(errno));
+ exit (CUPS_BACKEND_FAILED);
+ }
+ else if (pid < 0)
+ {
+ fprintf(stderr, "ERROR: Unable to fork for backend\n");
+ return (CUPS_BACKEND_FAILED);
+ }
+
+ while ((wait_pid = wait(&wait_status)) < 0 && errno == EINTR);
+
+ if (wait_pid >= 0 && wait_status)
+ {
+ if (WIFEXITED(wait_status))
+ retval = WEXITSTATUS(wait_status);
+ else if (WTERMSIG(wait_status) != SIGTERM)
+ retval = WTERMSIG(wait_status);
+ else
+ retval = 0;
+ }
return (retval);
}
@@ -304,8 +361,10 @@ sigterm_handler(int sig) // I - Signal number (unused)
{
(void)sig;
- fprintf(stderr,
- "DEBUG: beh: Job canceled.\n");
+ const char * const msg = "DEBUG: beh: Job canceled.\n";
+ // The if() is to eliminate the return value and silence the warning
+ // about an unused return value.
+ if (write(2, msg, strlen(msg)));
if (job_canceled)
_exit(CUPS_BACKEND_OK);
--
2.40.1

6
cups-filters.spec
View File

@ -15,7 +15,7 @@ Summary: OpenPrinting CUPS filters and backends for CUPS 2.X
Name: cups-filters
Epoch: 1
Version: 2.0~rc1
Release: 1%{?dist}
Release: 2%{?dist}
# the CUPS exception text is the same as LLVM exception, so using that name with
# agreement from legal team
@ -27,6 +27,7 @@ Source0: %{URL}/releases/download/%{upstream_version}/%{name}-%{upstream_version
# Patches
Patch0001: 0001-Merge-pull-request-from-GHSA-gpxc-v2m8-fr3x.patch
# autogen.sh
@ -176,6 +177,9 @@ make check
%changelog
* Wed May 17 2023 Zdenek Dohnal <zdohnal@redhat.com> - 1:2.0~rc1-2
- 2207970 - CVE-2023-24805 cups-filters: remote code execution in cups-filters, beh CUPS backend
* Thu Apr 27 2023 Zdenek Dohnal <zdohnal@redhat.com> - 1:2.0~rc1-1
- 2.0rc1