bugGNU troff - Bugs: bug #60977, [troff]: uses sprintf to write to...

 
 

bug #60977: [troff]: uses sprintf to write to buffer using user-controlled format string

Submitted by:  G. Branden Robinson <gbranden>
Submitted on:  Tue 27 Jul 2021 01:48:32 AM UTC  
 
Category:  Core Severity:  4 - Important
Item Group:  Warning/Suspicious behaviour Status:  Fixed
Privacy:  Public Assigned to:  G. Branden Robinson <gbranden>
Open/Closed:  Closed Planned Release:  1.23.0

Add a New Comment (Rich Markup)
   

You are not logged in

Please log in, so followups can be emailed to you.

 

Wed 28 Jul 2021 02:35:41 AM UTC, comment #2: 

Fixed as noted in comment #1.

G. Branden Robinson <gbranden>
Project AdministratorIn charge of this item.
Tue 27 Jul 2021 11:07:47 PM UTC, comment #1: 

Current WIP.

commit fd18b00bba9a4faf0318270380f5cceb86eba5b7
Author:     G. Branden Robinson <g.branden.robinson@gmail.com>
AuthorDate: Tue Jul 27 16:51:21 2021 +1000
Commit:     G. Branden Robinson <g.branden.robinson@gmail.com>
CommitDate: Tue Jul 27 17:46:05 2021 +1000

    [troff]: Fix Savannah #60977.

    [troff]: Avoid using sprintf() with user-controlled format string.

    * src/preproc/html/pre-html.cpp (makeFileName): Add comment noting need
      for implementation synchrony between this function, which generates
      \O5 escape sequences, and troff's suppress_node::tprint member
      function, which interprets them.

    * src/roff/troff/node.cpp: Rename 2 static globals for clarity.
      - `last_image_filename` -> `image_filename`
      - `last_image_id` -> `subimage_counter`

      (suppress_node::tprint): Set up the buffer for image file name to be
      written using a constant rather than an embedded literal.
      Unconditionally initialize the buffer with a string terminator, so
      there is no chance of a read from unitialized storage.  Drop unused
      code involving `tem`.  Drop stale comments.  Clarify comment: an
      `image_filename` doesn't _always_ contain a format string, only
      sometimes.  Replace use of `sprintf` with manual construction of a new
      image filename string.  There are two cases, one where a format string
      {presently "%d"} is present, and one where it is not.  If it is
      present, locate it {`percent`}.  This means a limited/bounded image
      ("subimage") is being processed; increment the subimage counter.
      Write a new image file name preserving the parts before and after "%d"
      (the "prefix" and "suffix", and replacing only the middle, using
      `sprintf` with the subimage counter and the (string literal) format.
      Be mindful of string bounds and memory allocation, issuing diagnostics
      or aborting as necessary.  If the image file name does _not_ contain a
      format string, but needs only to be copied, do that (`strcpy`), again
      instead of using `sprintf`.

    Fixes <https://savannah.gnu.org/bugs/?60977>.

    Implementation note:
    * Why all these standard C library string manipulations?  (1) I'm more
      familiar with C than C++.  (2) The inbound type I'm dealing with,
      {last,}image_filename, is a char*, not a C++ string type.  (3) groff
      does not use a standard C++ library string type, but its own
      implementation[1]; groff is _old_).  (4) That custom string class
      does not have any `printf`-style format methods that I can see.
      Incidentally, groff's own `i_to_a` library function[2] doesn't handle
      long ints, which `size_t` is, so you can't put longs into diagnostic
      messages among other places.  (It looks easy to change `i_to_a` and
      `ui_to_a` to support longs.  You can then watch the build explode into
      a thousand pieces with numeric overflows in troff.)  (5) I did attempt
      to handle the strings efficiently, never calling strcat() since I
      always knew where the end of a string I wanted to append to was[3].

    [1] src/include/stringclass.h
    [2] src/libs/libgroff/itoa.c
    [3] https://symas.com/the-sad-state-of-c-strings/

diff --git a/src/preproc/html/pre-html.cpp b/src/preproc/html/pre-html.cpp
index 88fcca18..501e90cb 100644
--- a/src/preproc/html/pre-html.cpp
+++ b/src/preproc/html/pre-html.cpp
@@ -544,6 +544,7 @@ static void makeFileName(void)
   if (image_template == NULL)
     sys_fatal("malloc");
   strcpy(image_template, macroset_template);
+  // Keep this format string synced with troff:suppress_node::tprint().
   strcat(image_template, "%d");
}

diff --git a/src/roff/troff/node.cpp b/src/roff/troff/node.cpp
index f2fc6da8..86b054e8 100644
--- a/src/roff/troff/node.cpp
+++ b/src/roff/troff/node.cpp
@@ -4053,8 +4053,8 @@ void suppress_node::put(troff_output_file *out, const char *s)
  */

static char last_position = 0;
-static const char *last_image_filename = 0;
-static int last_image_id = 0;
+static const char *image_filename = 0;
+static int subimage_counter = 0;

inline int min(int a, int b)
{
@@ -4086,23 +4086,62 @@ void suppress_node::tprint(troff_output_file *out)
   if (is_on == 2) {
     // remember position and filename
     last_position = position;
-    char *tem = (char *)last_image_filename;
-    last_image_filename = strsave(filename.contents());
-    if (tem)
-      free(tem);
-    last_image_id = image_id;
-    // printf("start of image and page = %d\n", current_page);
+    image_filename = strsave(filename.contents());
   }
   else {
-    // now check whether the suppress node requires us to issue limits.
+    // Now check whether the suppress node requires us to issue limits.
     if (emit_limits) {
-      char name[8192];
-      // remember that the filename will contain a %d in which the
-      // last_image_id is placed
-      if (last_image_filename == (char *) 0)
-       *name = '\0';
-      else
-       sprintf(name, last_image_filename, last_image_id);
+      const size_t namebuflen = 8192;
+      char name[namebuflen] = { '\0' };
+      // Jump through a flaming hoop to avoid a "format nonliteral"
+      // warning from blindly using sprintf...and avoid trouble from
+      // mischievous image stems.
+      //
+      // Keep this format string synced with pre-html:makeFileName().
+      const char format[] = "%d";
+      const size_t format_len = strlen(format);
+      const char *percent_position = strstr(image_filename, format);
+      if (percent_position) {
+       subimage_counter++;
+       assert(sizeof subimage_counter <= 8);
+       // A 64-bit signed int produces up to 19 decimal digits.
+       char *subimage_number = (char *)malloc(20); // 19 digits + \0
+       if (0 == subimage_number)
+         fatal("memory allocation failure");
+       // Replace the %d in the filename with this number.
+       size_t enough = strlen(image_filename) + 19 - format_len;
+       char *new_name = (char *)malloc(enough);
+       if (0 == new_name)
+         fatal("memory allocation failure");
+       ptrdiff_t prefix_length = percent_position - image_filename;
+       strncpy(new_name, image_filename, prefix_length);
+       sprintf(subimage_number, "%d", subimage_counter);
+       size_t number_length = strlen(subimage_number);
+       strcpy(new_name + prefix_length, subimage_number);
+       // Skip over the format in the source string.
+       const char *suffix_src = image_filename + prefix_length
+         + format_len;
+       char *suffix_dst = new_name + prefix_length + number_length;
+       strcpy(suffix_dst, suffix_src);
+       // Ensure the new string fits with room for a terminal '\0'.
+       const size_t len = strlen(new_name);
+       if (len > (namebuflen - 1))
+         error("constructed file name in suppressed output escape is"
+               " too long (>= %1 bytes); skipping image",
+               (int)namebuflen);
+       else
+         strncpy(name, new_name, (namebuflen - 1));
+       free(new_name);
+       free(subimage_number);
+      }
+      else {
+       const size_t len = strlen(image_filename);
+       if (len > (namebuflen - 1))
+         error("file name in suppressed output escape is too long"
+               " (>= %1 bytes); skipping image", (int)namebuflen);
+       else
+         strcpy(name, image_filename);
+      }
       if (is_html) {
        switch (last_position) {
        case 'c':

G. Branden Robinson <gbranden>
Project AdministratorIn charge of this item.
Tue 27 Jul 2021 01:48:32 AM UTC, original submission:  

A compiler warning points out a legitimate issue.

../src/roff/troff/node.cpp: In member function ‘virtual void suppress_node::tprint(troff_output_file*)’:
../src/roff/troff/node.cpp:4105:50: warning: format not a string literal, argument types not checked [-Wformat-nonliteral]
  sprintf(name, last_image_filename, last_image_id);
                                                  ^

In this case the format string, "last_image_filename", comes from an \O5 escape sequence, such as `\O[5lfoobar-%d.png]`.

I haven't been able to force anything untoward to happen using this escape sequence in a groff REPL, but I didn't try very hard and I am not an experienced system penetrator.

I have a fix in progress.

diff --git a/src/preproc/html/pre-html.cpp b/src/preproc/html/pre-html.cpp
index 88fcca18..66618c1f 100644
--- a/src/preproc/html/pre-html.cpp
+++ b/src/preproc/html/pre-html.cpp
@@ -544,6 +544,7 @@ static void makeFileName(void)
   if (image_template == NULL)
     sys_fatal("malloc");
   strcpy(image_template, macroset_template);
+  // Keep format string synced with troff:suppress_node::tprint().
   strcat(image_template, "%d");
}

diff --git a/src/roff/troff/node.cpp b/src/roff/troff/node.cpp
index f2fc6da8..87cd0d60 100644
--- a/src/roff/troff/node.cpp
+++ b/src/roff/troff/node.cpp
@@ -4053,8 +4053,8 @@ void suppress_node::put(troff_output_file *out, const char *s)
  */

static char last_position = 0;
-static const char *last_image_filename = 0;
-static int last_image_id = 0;
+static const char *image_filename = 0;
+static int subimage_counter = 0;

inline int min(int a, int b)
{
@@ -4086,23 +4086,53 @@ void suppress_node::tprint(troff_output_file *out)
   if (is_on == 2) {
     // remember position and filename
     last_position = position;
-    char *tem = (char *)last_image_filename;
-    last_image_filename = strsave(filename.contents());
-    if (tem)
-      free(tem);
-    last_image_id = image_id;
-    // printf("start of image and page = %d\n", current_page);
+    image_filename = strsave(filename.contents());
   }
   else {
-    // now check whether the suppress node requires us to issue limits.
+    // Now check whether the suppress node requires us to issue limits.
     if (emit_limits) {
       char name[8192];
-      // remember that the filename will contain a %d in which the
-      // last_image_id is placed
-      if (last_image_filename == (char *) 0)
+      if (image_filename == (char *) 0)
        *name = '\0';
-      else
-       sprintf(name, last_image_filename, last_image_id);
+      else {
+       // Jump through a flaming hoop to avoid a "format nonliteral"
+       // warning from blindly using sprintf...and avoid trouble from
+       // mischievous image stems.
+       //
+       // Keep this format string synced with pre-html:makeFileName().
+       const char format[] = "%d";
+       const size_t format_len = strlen(format);
+       const char *percent_position = strstr(image_filename, format);
+       if (percent_position) {
+         subimage_counter++;
+         assert(sizeof subimage_counter <= 8);
+         // A 64-bit signed int produces up to 19 decimal digits.
+         char *subimage_number = (char *)malloc(20); // 19 digits + \0
+         if (0 == subimage_number)
+           fatal("memory allocation failure");
+         // Replace the %d in the filename with this number.
+         size_t enough = strlen(image_filename) + 19 - format_len;
+         char *new_name = (char *)malloc(enough);
+         if (0 == new_name)
+           fatal("memory allocation failure");
+         ptrdiff_t prefix_length = percent_position - image_filename;
+         strncpy(new_name, image_filename, prefix_length);
+         sprintf(subimage_number, "%d", subimage_counter);
+         size_t number_length = strlen(subimage_number);
+         strcpy(new_name + prefix_length, subimage_number);
+         // Skip over the format in the source string.
+         const char *suffix_src = image_filename + prefix_length
+           + format_len;
+         char *suffix_dst = new_name + prefix_length + number_length;
+         strcat(suffix_dst, suffix_src);
+         assert(strlen(new_name) < 8191);
+         strncpy(name, new_name, 8191);
+         free(new_name);
+         free(subimage_number);
+       }
+       else
+         strcpy(name, image_filename);
+      }
       if (is_html) {
        switch (last_position) {
        case 'c':

G. Branden Robinson <gbranden>
Project AdministratorIn charge of this item.

 

(Note: upload size limit is set to 16384 kB, after insertion of the required escape characters.)

Attach Files:
   
   
Comment:
   

No files currently attached

 

Depends on the following items: None found

Items that depend on this one: None found

 

Carbon-Copy List
  • -email is unavailable- added by gbranden (Submitted the item)
  •  

    Do you think this task is very important?
    If so, you can add your encouragement to it.
    This task has 0 encouragements so far.

    Only logged-in users can vote.

     

     

     

    Follow 4 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2021-07-28 gbranden Open/ClosedOpen => Closed
        Planned ReleaseNone => 1.23.0
    2021-07-28 gbranden Item GroupNone => Warning/Suspicious behaviour
        StatusIn Progress => Fixed

    Back to the top


    Powered by Savane 3.7