| Summary: | GC segfault on encoded bitmap | ||
|---|---|---|---|
| Product: | Ghostscript | Reporter: | Stephen McCamant <smcc> |
| Component: | PS Interpreter | Assignee: | Alex Cherepanov <alex> |
| Status: | RESOLVED DUPLICATE | ||
| Severity: | normal | ||
| Priority: | P2 | ||
| Version: | master | ||
| Hardware: | PC | ||
| OS: | Linux | ||
| Customer: | Word Size: | --- | |
| Attachments: | Example input that causes the segfault | ||
Thanks could I get you to attach the test file as an attachment and give the commandline you used to get it to fail. Thanks. Created attachment 1366 [details] Example input that causes the segfault To reproduce: gs bug688075.ps </dev/null where bug688075.ps is the attachment. In lieu of the "</dev/null", you can also just signal end-of-file at the "GS>" prompt. I can reproduce the bug on peeves.ghostscript.com, GS 8.30, but I cannot reproduce the bug on Windows XP under Cygwin (GCC 3.3.3) or MSVC6 executables. I've done a little more basic investigation:
If I compile with debugging, the segfault happens in ialloc_validate_chunk
instead of gc_objects_clear_marks, but the relevant code looks similar:
314 struct_proc_enum_ptrs((*proc)) = pre->o_type->enum_ptrs;
I was previously mislead by the hairy macro that's getting expanded there;
I think the problem is actually not that proc is being dereferences as a null
pointer, but that the initialization of proc is accessing an out of bounds
pointer. The expanded code looks like:
proc = pre->d.o.t.type->enum_ptrs
but pre->d.o.t.type is a bogus value (0x933b080 here). With the help of a
watchpoint, I can see where it's getting corrupted, in cf_decode_2d:
693 invert_data(dlen, black_byte, DO_NOTHING, idd);
This line changes the address later accessed as pre->d.o.t.type from
0x833b080 (which is a valid pointer) into the bad 0x933b080 value. I suspect
it's overrunning a buffer and treating part of a pointer as if it were
image data. ("dlen" is 42, which is one larger than the declared width of
the image.)
Does ghostscript support compiling in a "Purify" or "Valgrind" mode where it
uses plain old malloc() rather than its garbage collector? That might make
debugging this sort of problem easier.
It looks as a problem in scfd.c Passing to Alex who owns that module. I think there is no need to reproduce segfault on Windows. Just see what happens while processing the filter. Likely it writes outside the buffer. |
When I try to display a PS file that contains a certain CCITT-encoded bitmap, Ghostscript will reliably segfault slightly later in execution (at exit, for a small example). The crash also occurs when I try to view a PDF file containing the same image (the PS file was created from the PDF file with pstopdf). xpdf can view the same PDF file without problems; acroread 5 displays some errors, but does not crash. (The PDF file appears to have been generated with an old version of Ghostscript, 5.03). Even if the image is somehow illegal, though, I don't think Ghostscript should crash. The crash is a null pointer dereference that occurs in garbage collection code. Here's the backtrace: #0 0x080fbc65 in gc_objects_clear_marks (mem=0x83d813c, cp=0x8541750) at src/igc.c:582 #1 0x080fae23 in gs_gc_reclaim (pspaces=0x83f9aa8, global=1) at src/igc.c:263 #2 0x081782d9 in context_reclaim (pspaces=0x83f9aa8, global=1) at src/zcontext.c:286 #3 0x080d0e54 in gs_vmreclaim (dmem=0x83f9aa4, global=1) at src/ireclaim.c:156 #4 0x080d0c4b in ireclaim (dmem=0x83f9aa4, space=8) at src/ireclaim.c:78 #5 0x080cba77 in interp_reclaim (pi_ctx_p=0x83d7eac, space=8) at src/interp.c:419 #6 0x080c353f in gs_main_finit (minst=0x83d7cd8, exit_status=0, code=0) at src/imain.c:834 #7 0x080c3804 in gs_to_exit_with_code (mem=0x83d7c40, exit_status=0, code=0) at src/imain.c:898 #8 0x0804b06c in main (argc=2, argv=0xbffff8b4) at src/gs.c:89 The line where the segfault occurs is: 582 struct_proc_clear_marks((*proc)) = "proc" is 0. Here is an example file that causes the crash: << /ImageType 1 /Width 41 /Height 53 /ImageMatrix [41 0 0 -53 0 53] /BitsPerComponent 1 /DataSource currentfile /ASCII85Decode filter << /K -1 /Columns 41 >> /CCITTFaxDecode filter >> imagemask 21]lq#&Y.eV>*>aTe%\1$gV0p6i+[q#1HrT0jbH?+90%B)tk71OPn%E%#/K"RXiBX +9Dl~> %-EOD- I've been able to reproduce this with all the Ghostscript versions I have handy, ranging from 8.01 to today's CVS checkout.