bug#9428: Emacs mishandles file offsets > 2**29 bytes

[Paul Eggert]

Package: Emacs
Version: 24.0.50
Tags: patch

This patch fixes some integer-overflow issues with large files, mostly
on 32-bit hosts.  I plan to test it a bit more before installing.

=== modified file 'src/ChangeLog'
--- src/ChangeLog       2011-08-30 22:43:43 +0000
+++ src/ChangeLog       2011-09-03 05:23:17 +0000
@@ -1,3 +1,22 @@
+2011-09-03  Paul Eggert  <eggert@cs.ucla.edu>
+
+       * fileio.c: Fix bugs with large file offsets.
+       The previous code assumed that file offsets (off_t values) fit in
+       EMACS_INT variables, which is not true on typical 32-bit hosts.
+       The code messed up by falsely reporting buffer overflow in cases
+       such as (insert-file-contents "big" nil 1 2) into an empty buffer
+       when "big" contains more than 2**29 bytes, even though this
+       inserts just one byte and does not overflow the buffer.
+       (Finsert_file_contents): Store file offsets as off_t
+       values, not as EMACS_INT values.  Check for overflow when
+       converting between EMACS_INT and off_t.  When checking for
+       buffer overflow or for overlap, take the offsets into account.
+       Don't use EMACS_INT for small values where int suffices.
+       When checking for overlap, fix a typo: ZV was used where
+       ZV_BYTE was intended.
+       (Fwrite_region): Don't assume off_t fits into 'long'.
+       * buffer.h (struct buffer.modtime_size): Now off_t, not EMACS_INT.
+
 2011-08-30  Chong Yidong  <cyd@stupidchicken.com>
 
        * syntax.c (find_defun_start): Update all cache variables if

=== modified file 'src/buffer.h'
--- src/buffer.h        2011-07-06 21:53:56 +0000
+++ src/buffer.h        2011-09-03 05:23:17 +0000
@@ -559,7 +559,7 @@
      is still the same (since it's rounded up to seconds) but we're actually
      not up-to-date.  -1 means the size is unknown.  Only meaningful if
      modtime is actually set.  */
-  EMACS_INT modtime_size;
+  off_t modtime_size;
   /* The value of text->modiff at the last auto-save.  */
   int auto_save_modified;
   /* The value of text->modiff at the last display error.

=== modified file 'src/fileio.c'
--- src/fileio.c        2011-07-19 20:37:27 +0000
+++ src/fileio.c        2011-09-03 05:23:17 +0000
@@ -3179,6 +3179,7 @@
   EMACS_INT inserted = 0;
   int nochange = 0;
   register EMACS_INT how_much;
+  off_t beg_offset, end_offset;
   register EMACS_INT unprocessed;
   int count = SPECPDL_INDEX ();
   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4, gcpro5;
@@ -3284,15 +3285,6 @@
   record_unwind_protect (close_file_unwind, make_number (fd));
 
 
-  /* Check whether the size is too large or negative, which can happen on a
-     platform that allows file sizes greater than the maximum off_t value.  */
-  if (! not_regular
-      && ! (0 <= st.st_size && st.st_size <= BUF_BYTES_MAX))
-    buffer_overflow ();
-
-  /* Prevent redisplay optimizations.  */
-  current_buffer->clip_changed = 1;
-
   if (!NILP (visit))
     {
       if (!NILP (beg) || !NILP (end))
@@ -3302,25 +3294,63 @@
     }
 
   if (!NILP (beg))
-    CHECK_NUMBER (beg);
+    {
+      if (! (RANGED_INTEGERP (0, beg, TYPE_MAXIMUM (off_t))))
+       wrong_type_argument (intern ("file-offset"), beg);
+      beg_offset = XFASTINT (beg);
+    }
   else
-    XSETFASTINT (beg, 0);
+    beg_offset = 0;
 
   if (!NILP (end))
-    CHECK_NUMBER (end);
+    {
+      if (! (RANGED_INTEGERP (0, end, TYPE_MAXIMUM (off_t))))
+       wrong_type_argument (intern ("file-offset"), end);
+      end_offset = XFASTINT (end);
+    }
   else
     {
-      if (! not_regular)
+      if (not_regular)
+       end_offset = TYPE_MAXIMUM (off_t);
+      else
        {
-         XSETINT (end, st.st_size);
+         end_offset = st.st_size;
+
+         /* A negative size can happen on a platform that allows file
+            sizes greater than the maximum off_t value.  */
+         if (end_offset < 0)
+           buffer_overflow ();
 
          /* The file size returned from stat may be zero, but data
             may be readable nonetheless, for example when this is a
             file in the /proc filesystem.  */
-         if (st.st_size == 0)
-           XSETINT (end, READ_BUF_SIZE);
-       }
-    }
+         if (end_offset == 0)
+           end_offset = READ_BUF_SIZE;
+       }
+    }
+
+  /* Check now whether the buffer will become too large,
+     in the likely case where the file's length is not changing.
+     This saves a lot of needless work before a buffer overflow.  */
+  if (! not_regular)
+    {
+      /* The likely offset where we will stop reading.  We could read
+        more (or less), if the file grows (or shrinks) as we read it.  */
+      off_t likely_end = min (end_offset, st.st_size);
+
+      if (beg_offset < likely_end)
+       {
+         ptrdiff_t buf_bytes =
+           Z_BYTE - (!NILP (replace) ? ZV_BYTE - BEGV_BYTE  : 0);
+         ptrdiff_t buf_growth_max = BUF_BYTES_MAX - buf_bytes;
+         off_t likely_growth = likely_end - beg_offset;
+         if (buf_growth_max < likely_growth)
+           buffer_overflow ();
+       }
+    }
+
+  /* Prevent redisplay optimizations.  */
+  current_buffer->clip_changed = 1;
 
   if (EQ (Vcoding_system_for_read, Qauto_save_coding))
     {
@@ -3465,9 +3495,9 @@
         give up on handling REPLACE in the optimized way.  */
       int giveup_match_end = 0;
 
-      if (XINT (beg) != 0)
+      if (beg_offset != 0)
        {
-         if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+         if (lseek (fd, beg_offset, SEEK_SET) < 0)
            report_file_error ("Setting file position",
                               Fcons (orig_filename, Qnil));
        }
@@ -3515,7 +3545,7 @@
       immediate_quit = 0;
       /* If the file matches the buffer completely,
         there's no need to replace anything.  */
-      if (same_at_start - BEGV_BYTE == XINT (end))
+      if (same_at_start - BEGV_BYTE == end_offset)
        {
          emacs_close (fd);
          specpdl_ptr--;
@@ -3530,16 +3560,17 @@
         already found that decoding is necessary, don't waste time.  */
       while (!giveup_match_end)
        {
-         EMACS_INT total_read, nread, bufpos, curpos, trial;
+         int total_read, nread, bufpos, trial;
+         off_t curpos;
 
          /* At what file position are we now scanning?  */
-         curpos = XINT (end) - (ZV_BYTE - same_at_end);
+         curpos = end_offset - (ZV_BYTE - same_at_end);
          /* If the entire file matches the buffer tail, stop the scan.  */
          if (curpos == 0)
            break;
          /* How much can we scan in the next step?  */
          trial = min (curpos, sizeof buffer);
-         if (emacs_lseek (fd, curpos - trial, SEEK_SET) < 0)
+         if (lseek (fd, curpos - trial, SEEK_SET) < 0)
            report_file_error ("Setting file position",
                               Fcons (orig_filename, Qnil));
 
@@ -3606,13 +3637,14 @@
 
          /* Don't try to reuse the same piece of text twice.  */
          overlap = (same_at_start - BEGV_BYTE
-                    - (same_at_end + st.st_size - ZV));
+                    - (same_at_end
+                       + (! NILP (end) ? end_offset : st.st_size) - ZV_BYTE));
          if (overlap > 0)
            same_at_end += overlap;
 
          /* Arrange to read only the nonmatching middle part of the file.  */
-         XSETFASTINT (beg, XINT (beg) + (same_at_start - BEGV_BYTE));
-         XSETFASTINT (end, XINT (end) - (ZV_BYTE - same_at_end));
+         beg_offset += same_at_start - BEGV_BYTE;
+         end_offset -= ZV_BYTE - same_at_end;
 
          del_range_byte (same_at_start, same_at_end, 0);
          /* Insert from the file at the proper position.  */
@@ -3657,7 +3689,7 @@
       /* First read the whole file, performing code conversion into
         CONVERSION_BUFFER.  */
 
-      if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+      if (lseek (fd, beg_offset, SEEK_SET) < 0)
        report_file_error ("Setting file position",
                           Fcons (orig_filename, Qnil));
 
@@ -3824,7 +3856,7 @@
     }
 
   if (! not_regular)
-    total = XINT (end) - XINT (beg);
+    total = end_offset - beg_offset;
   else
     /* For a special file, all we can do is guess.  */
     total = READ_BUF_SIZE;
@@ -3845,9 +3877,9 @@
   if (GAP_SIZE < total)
     make_gap (total - GAP_SIZE);
 
-  if (XINT (beg) != 0 || !NILP (replace))
+  if (beg_offset != 0 || !NILP (replace))
     {
-      if (emacs_lseek (fd, XINT (beg), SEEK_SET) < 0)
+      if (lseek (fd, beg_offset, SEEK_SET) < 0)
        report_file_error ("Setting file position",
                           Fcons (orig_filename, Qnil));
     }
@@ -4576,7 +4608,7 @@
 
   if (!NILP (append) && !NILP (Ffile_regular_p (filename)))
     {
-      long ret;
+      off_t ret;
 
       if (NUMBERP (append))
        ret = emacs_lseek (desc, XINT (append), SEEK_CUR);