[Buildroot] [PATCH 1/1] package/cups-filters: fix CVE-2023-24805

* [Buildroot] [PATCH 1/1] package/cups-filters: fix CVE-2023-24805
@ 2023-10-01 19:15 Fabrice Fontaine
  2023-11-04 20:16 ` Thomas Petazzoni via buildroot
  2023-11-09 11:17 ` Peter Korsgaard
  0 siblings, 2 replies; 3+ messages in thread
From: Fabrice Fontaine @ 2023-10-01 19:15 UTC (permalink / raw)
  To: buildroot; +Cc: Angelo Compagnucci, Olivier Schonken, Fabrice Fontaine

Fix CVE-2023-24805: cups-filters contains backends, filters, and other
software required to get the cups printing service working on operating
systems other than macos. If you use the Backend Error Handler (beh) to
create an accessible network printer, this security vulnerability can
cause remote code execution. `beh.c` contains the line `retval =
system(cmdline) >> 8;` which calls the `system` command with the operand
`cmdline`. `cmdline` contains multiple user controlled, unsanitized
values. As a result an attacker with network access to the hosted print
server can exploit this vulnerability to inject system commands which
are executed in the context of the running server. This issue has been
addressed in commit `8f2740357` and is expected to be bundled in the
next release. Users are advised to upgrade when possible and to restrict
access to network printers in the meantime.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
---
 ...ecv-instead-of-system-CVE-2023-24805.patch | 208 ++++++++++++++++++
 package/cups-filters/cups-filters.mk          |   3 +
 2 files changed, 211 insertions(+)
 create mode 100644 package/cups-filters/0001-beh-backend-Use-execv-instead-of-system-CVE-2023-24805.patch

diff --git a/package/cups-filters/0001-beh-backend-Use-execv-instead-of-system-CVE-2023-24805.patch b/package/cups-filters/0001-beh-backend-Use-execv-instead-of-system-CVE-2023-24805.patch
new file mode 100644
index 0000000000..e527b20f91
--- /dev/null
+++ b/package/cups-filters/0001-beh-backend-Use-execv-instead-of-system-CVE-2023-24805.patch
@@ -0,0 +1,208 @@
+From 93e60d3df358c0ae6f3dba79e1c9684657683d89 Mon Sep 17 00:00:00 2001
+From: Till Kamppeter <till.kamppeter@gmail.com>
+Date: Wed, 17 May 2023 11:11:29 +0200
+Subject: [PATCH] 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 a forged job title.
+
+In addition, done the following fixes and improvements:
+
+- Do not allow '/' in the scheme of the URI (= backend executable
+  name), to assure that only backends inside /usr/lib/cups/backend/
+  are used.
+
+- URI must have ':', to split off scheme, otherwise error out.
+
+- 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.
+
+- 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.
+
+Upstream: https://github.com/OpenPrinting/cups-filters/commit/93e60d3df358c0ae6f3dba79e1c9684657683d89
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+---
+ backend/beh.c | 107 +++++++++++++++++++++++++++++++++++++++-----------
+ 1 file changed, 84 insertions(+), 23 deletions(-)
+
+diff --git a/backend/beh.c b/backend/beh.c
+index 225fd27d5..8d51235b1 100644
+--- a/backend/beh.c
++++ b/backend/beh.c
+@@ -22,12 +22,13 @@
+ #include "backend-private.h"
+ #include <cups/array.h>
+ #include <ctype.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 */
+ 
+ /*
+  * Local functions...
+@@ -213,21 +214,40 @@ call_backend(char *uri,                 /* I - URI of final destination */
+ 	     char **argv,		/* I - Command-line arguments */
+ 	     char *filename) {          /* I - File name of input data */
+   const char	*cups_serverbin;	/* Location of programs */
++  char          *backend_argv[8];	/* Arguments for 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 = 0, 		/* Process ID of backend */
++                wait_pid,		/* Process ID from wait() */
++                wait_status, 		/* Status from child */
++                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;
+ 
+@@ -235,16 +255,29 @@ call_backend(char *uri,                 /* I - URI of final destination */
+     fprintf(stderr,
+ 	    "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];
++  /* 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 */
++  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);
++    return (CUPS_BACKEND_FAILED);
++  }
+ 
+  /*
+   * Overwrite the device URI and run the actual backend...
+@@ -253,18 +286,44 @@ 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\"...\n",
++	  backend_path, backend_argv[1], backend_argv[2], backend_argv[3],
++	  backend_argv[4], backend_argv[5], backend_argv[6]);
+   fprintf(stderr,
+ 	  "DEBUG: beh: Using device URI: %s\n",
+ 	  uri);
+ 
+-  retval = system(cmdline) >> 8;
++  if ((pid = fork()) == 0) {
++   /*
++    * Child comes here...
++    */
++
++    /* Run the backend */
++    execv(backend_path, backend_argv);
+ 
+-  if (retval == -1)
+     fprintf(stderr, "ERROR: Unable to execute backend command line: %s\n",
+ 	    strerror(errno));
+ 
++    exit(1);
++  } else if (pid < 0) {
++   /*
++    * Unable to fork!
++    */
++
++    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);
+ }
+ 
+@@ -277,8 +336,10 @@ static void
+ 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);
diff --git a/package/cups-filters/cups-filters.mk b/package/cups-filters/cups-filters.mk
index 19c859e602..dcfb2e9500 100644
--- a/package/cups-filters/cups-filters.mk
+++ b/package/cups-filters/cups-filters.mk
@@ -10,6 +10,9 @@ CUPS_FILTERS_LICENSE = GPL-2.0, GPL-2.0+, GPL-3.0, GPL-3.0+, LGPL-2, LGPL-2.1+,
 CUPS_FILTERS_LICENSE_FILES = COPYING
 CUPS_FILTERS_CPE_ID_VENDOR = linuxfoundation
 
+# 0001-beh-backend-Use-execv-instead-of-system-CVE-2023-24805.patch
+CUPS_FILTERS_IGNORE_CVES += CVE-2023-24805
+
 CUPS_FILTERS_DEPENDENCIES = cups libglib2 lcms2 qpdf fontconfig freetype jpeg
 
 CUPS_FILTERS_CONF_OPTS = \
-- 
2.40.1

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