* PATCH: fix for memory corruption and eventual crash in print.c
@ 2008-07-06 4:11 Ami Fischman
2008-07-06 7:45 ` YAMAMOTO Mitsuharu
2008-07-21 5:06 ` Chong Yidong
0 siblings, 2 replies; 6+ messages in thread
From: Ami Fischman @ 2008-07-06 4:11 UTC (permalink / raw)
To: emacs-devel
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src/print.c:print_object() has this code:
1570 if (NILP (Vprint_circle) && NILP (Vprint_gensym))
[...]
1581 being_printed[print_depth] = obj;
[...]
1611 print_depth++;
1612
1613 /* See similar code in print_preprocess. */
1614 if (print_depth > PRINT_CIRCLE)
1615 error ("Apparently circular structure being printed");
Note that being_printed[print_depth] is assigned to /before/ print_depth is
checked for exceeding PRINT_CIRCLE (the declared size of being_printed).
Here's a snippet of elisp that exhibits the bug:
(let ((print-circle nil)
(i 0))
(require 'cl)
(setq x '(a b))
(while (< i 200)
(incf i)
(setq x `(,x)))
(prin1-to-string x))
This errors with "Apparently circular structure being printed". So far so
good. Now evaling:
(prin1-to-string "hello")
errors with "Lisp nesting exceeds `max-lisp-eval-depth`" even though it
should be an easy thing to print!
Groveling with gdb shows that Vprin1_to_string_buffer gets overwritten
during the deep prin1 because of the bug above and instead of pointing at
the " prin1" buffer it has a value that pp's as a long chain of "[[[[[["'s
and errors out before completing the pretty-print.
Moving the guard check on print_depth above the assignment (and changing >
to >= because it's now above the print_depth++) makes the first elisp
snippet innocuous - eval'ing it still errors out about the apparently
circular structure, but subsequent prin1-to-string's work just fine.
Patch attached.
FWIW, I discovered the bug because using emacs-jabber was making my emacs
sessions unstable (at some point random standard elisp functions would start
failing). It turned out that one of its variables (jabber-connections) has
a deeply-enough nested component that this bug is triggered if it is
prin1'd.
Cheers,
-a
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diff --git a/src/print.c b/src/print.c
index 8fac266..b9d2e12 100644
--- a/src/print.c
+++ b/src/print.c
@@ -1560,6 +1560,10 @@ print_object (obj, printcharfun, escapeflag)
QUIT;
+ /* See similar code in print_preprocess. */
+ if (print_depth >= PRINT_CIRCLE)
+ error ("Apparently circular structure being printed");
+
/* Detect circularities and truncate them. */
if (STRINGP (obj) || CONSP (obj) || VECTORP (obj)
|| COMPILEDP (obj) || CHAR_TABLE_P (obj) || SUB_CHAR_TABLE_P (obj)
@@ -1610,9 +1614,6 @@ print_object (obj, printcharfun, escapeflag)
print_depth++;
- /* See similar code in print_preprocess. */
- if (print_depth > PRINT_CIRCLE)
- error ("Apparently circular structure being printed");
#ifdef MAX_PRINT_CHARS
if (max_print && print_chars > max_print)
{
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: PATCH: fix for memory corruption and eventual crash in print.c
2008-07-06 4:11 PATCH: fix for memory corruption and eventual crash in print.c Ami Fischman
@ 2008-07-06 7:45 ` YAMAMOTO Mitsuharu
2008-07-06 13:51 ` Chong Yidong
2008-07-21 5:06 ` Chong Yidong
1 sibling, 1 reply; 6+ messages in thread
From: YAMAMOTO Mitsuharu @ 2008-07-06 7:45 UTC (permalink / raw)
To: Ami Fischman; +Cc: emacs-devel
>>>>> On Sat, 5 Jul 2008 21:11:14 -0700, "Ami Fischman" <ami@fischman.org> said:
> src/print.c:print_object() has this code:
> 1570 if (NILP (Vprint_circle) && NILP (Vprint_gensym))
> [...]
> 1581 being_printed[print_depth] = obj;
> [...]
> 1611 print_depth++;
> 1612
> 1613 /* See similar code in print_preprocess. */
> 1614 if (print_depth > PRINT_CIRCLE)
> 1615 error ("Apparently circular structure being printed");
> Note that being_printed[print_depth] is assigned to /before/ print_depth is
> checked for exceeding PRINT_CIRCLE (the declared size of being_printed).
This reminds me of a similar buffer overrun that had existed in
`print_preprocess' also with respect to `being_printed'.
http://lists.gnu.org/archive/html/emacs-devel/2004-07/msg00146.html
I think a fix for `print_object' should go to the EMACS_22_BASE branch
as well as the trunk so it may not be missed. Another candidate for
the inclusion to the EMACS_22_BASE branch would be the PNG background
color bit-depth fix below:
2008-05-09 Chong Yidong <cyd@stupidchicken.com>
* image.c (png_load): Use correct bit-depth for setting background
color.
YAMAMOTO Mitsuharu
mituharu@math.s.chiba-u.ac.jp
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: PATCH: fix for memory corruption and eventual crash in print.c
2008-07-06 7:45 ` YAMAMOTO Mitsuharu
@ 2008-07-06 13:51 ` Chong Yidong
2008-07-07 10:03 ` YAMAMOTO Mitsuharu
0 siblings, 1 reply; 6+ messages in thread
From: Chong Yidong @ 2008-07-06 13:51 UTC (permalink / raw)
To: YAMAMOTO Mitsuharu; +Cc: Ami Fischman, emacs-devel
YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> writes:
> I think a fix for `print_object' should go to the EMACS_22_BASE branch
> as well as the trunk so it may not be missed. Another candidate for
> the inclusion to the EMACS_22_BASE branch would be the PNG background
> color bit-depth fix below:
>
> 2008-05-09 Chong Yidong <cyd@stupidchicken.com>
>
> * image.c (png_load): Use correct bit-depth for setting background
> color.
Yes. Could someone please check it into the branch? Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: PATCH: fix for memory corruption and eventual crash in print.c
2008-07-06 13:51 ` Chong Yidong
@ 2008-07-07 10:03 ` YAMAMOTO Mitsuharu
2008-07-07 13:56 ` Chong Yidong
0 siblings, 1 reply; 6+ messages in thread
From: YAMAMOTO Mitsuharu @ 2008-07-07 10:03 UTC (permalink / raw)
To: Chong Yidong; +Cc: Ami Fischman, emacs-devel
>>>>> On Sun, 06 Jul 2008 09:51:59 -0400, Chong Yidong <cyd@stupidchicken.com> said:
> YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> writes:
>> I think a fix for `print_object' should go to the EMACS_22_BASE branch
>> as well as the trunk so it may not be missed. Another candidate for
>> the inclusion to the EMACS_22_BASE branch would be the PNG background
>> color bit-depth fix below:
>>
>> 2008-05-09 Chong Yidong <cyd@stupidchicken.com>
>>
>> * image.c (png_load): Use correct bit-depth for setting background
>> color.
> Yes. Could someone please check it into the branch? Thanks.
Done for `png_load'. For the `print_object' patch offered by the OP,
I'd like to leave it to experts on this area.
YAMAMOTO Mitsuharu
mituharu@math.s.chiba-u.ac.jp
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: PATCH: fix for memory corruption and eventual crash in print.c
2008-07-07 10:03 ` YAMAMOTO Mitsuharu
@ 2008-07-07 13:56 ` Chong Yidong
0 siblings, 0 replies; 6+ messages in thread
From: Chong Yidong @ 2008-07-07 13:56 UTC (permalink / raw)
To: YAMAMOTO Mitsuharu; +Cc: Ami Fischman, emacs-devel
YAMAMOTO Mitsuharu <mituharu@math.s.chiba-u.ac.jp> writes:
>> Yes. Could someone please check it into the branch? Thanks.
>
> Done for `png_load'. For the `print_object' patch offered by the OP,
> I'd like to leave it to experts on this area.
Thanks.
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: PATCH: fix for memory corruption and eventual crash in print.c
2008-07-06 4:11 PATCH: fix for memory corruption and eventual crash in print.c Ami Fischman
2008-07-06 7:45 ` YAMAMOTO Mitsuharu
@ 2008-07-21 5:06 ` Chong Yidong
1 sibling, 0 replies; 6+ messages in thread
From: Chong Yidong @ 2008-07-21 5:06 UTC (permalink / raw)
To: Ami Fischman; +Cc: emacs-devel
"Ami Fischman" <ami@fischman.org> writes:
> src/print.c:print_object() has this code:
>
> 1570 if (NILP (Vprint_circle) && NILP (Vprint_gensym))
> [...]
> 1581 being_printed[print_depth] = obj;
> [...]
> 1611 print_depth++;
> 1612
> 1613 /* See similar code in print_preprocess. */
> 1614 if (print_depth > PRINT_CIRCLE)
> 1615 error ("Apparently circular structure being printed");
>
> Note that being_printed[print_depth] is assigned to /before/ print_depth is
> checked for exceeding PRINT_CIRCLE (the declared size of being_printed).
>
> Patch attached.
Thanks, I've checked in the fix (to both the trunk and the branch).
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2008-07-21 5:06 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz follow: Atom feed
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2008-07-06 4:11 PATCH: fix for memory corruption and eventual crash in print.c Ami Fischman
2008-07-06 7:45 ` YAMAMOTO Mitsuharu
2008-07-06 13:51 ` Chong Yidong
2008-07-07 10:03 ` YAMAMOTO Mitsuharu
2008-07-07 13:56 ` Chong Yidong
2008-07-21 5:06 ` Chong Yidong
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