Subject: bug#25041: closed (Re: bug#25041: Bugs in TAC and TAIL for closed stdin)

From: [email-masked] (GNU bug Tracking System)
Date: Sun, 27 Nov 2016 12:14:01 +0000

Your bug report

#25041: Bugs in TAC and TAIL for closed stdin

which was filed against the coreutils package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to [email-masked].

-- 
25041: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=25041
GNU Bug Tracking System
Contact [email-masked] with problems

Subject: Re: bug#25041: Bugs in TAC and TAIL for closed stdin
From: Pádraig Brady <[email-masked]>
To: Marcel Böhme <[email-masked]>, [email-masked]
Date: Sun, 27 Nov 2016 12:13:11 +0000
List-Id: <debbugs-submit.debbugs.gnu.org>

On 27/11/16 09:15, Marcel Böhme wrote:
> Dear all,
> 
> During fuzzing, we found one use-after-free in tac and one invalid-loading-of-value in tail.
> Interestingly, these errors can be observed only when stdin is externally closed but internally expected to be open.
> 
> The bugs were found by AFLFast, a fork of AFL. 
> The bug in tac was also found by Klee.
> Thanks again also to Van-Thuan Pham.
> 
> The following execution crashes TAC in trunk. For the same execution of preinstalled version 8.21 on Ubuntu x86_64, valgrind flags a few invalid reads of size 8. There is no problem in version 6.10:
> 
> $ ./tac - - <&-
> ./tac: 'standard input': read error: Bad file descriptor
> =================================================================
> ==53813==ERROR: AddressSanitizer: heap-use-after-free on address 0x61600000f990 at pc 0x00000040e127 bp 0x7ffefd0f76e0 sp 0x7ffefd0f76d8
> READ of size 8 at 0x61600000f990 thread T0
>     #0 0x40e126 in rpl_fseeko ../lib/fseeko.c:51
>     #1 0x4032ac in temp_stream ../src/tac.c:480
>     #2 0x4032ac in copy_to_temp ../src/tac.c:504
>     #3 0x4032ac in tac_nonseekable ../src/tac.c:553
>     #4 0x4032ac in tac_file ../src/tac.c:595
>     #5 0x4032ac in main ../src/tac.c:701
>     #6 0x7f135e464f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
>     #7 0x404779  (/home/ubuntu/subjects/coreutils/obj-gcov/src/tac+0x404779)
> 
> 0x61600000f990 is located 16 bytes inside of 568-byte region [0x61600000f980,0x61600000fbb8)
> freed by thread T0 here:
>     #0 0x7f135f5e1090 in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc2090)
>     #1 0x7f135e4b0a24 in _IO_fclose (/lib/x86_64-linux-gnu/libc.so.6+0x6da24)
> 
> previously allocated by thread T0 here:
>     #0 0x7f135f5e13a8 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc23a8)
>     #1 0x7f135e4b0c81 in fdopen (/lib/x86_64-linux-gnu/libc.so.6+0x6dc81)
> 
> SUMMARY: AddressSanitizer: heap-use-after-free ../lib/fseeko.c:51 in rpl_fseeko
> =================================================================

Oh right, we're operating on a closed stream here.
I'll fix that up.

> The following execution of TAIL in trunk is flagged by UBSAN.
> $ tail -f <&-
> tail.c:2220:18: runtime error: load of value 190, which is not a valid value for type ‘_Bool'

Right we need to init f->ignore in more cases.
I confirmed this no longer triggers the issue:

diff --git a/src/tail.c b/src/tail.c
index 5c75be0..3d83550 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -1940,8 +1940,6 @@ tail_file (struct File_spec *f, uintmax_t n_units)
               ok = false;
               f->errnum = -1;
               f->tailable = false;
-              f->ignore = ! (reopen_inaccessible_files
-                             && follow_mode == Follow_name);
               error (0, 0, _("%s: cannot follow end of this type of file%s"),
                      quotef (pretty_name (f)),
                      f->ignore ? _("; giving up on this name") : "");
@@ -1949,6 +1947,8 @@ tail_file (struct File_spec *f, uintmax_t n_units)

           if (!ok)
             {
+              f->ignore = ! (reopen_inaccessible_files
+                              && follow_mode == Follow_name);
               close_fd (fd, pretty_name (f));
               f->fd = -1;
             }

thanks!
Pádraig

Subject: Bugs in TAC and TAIL for closed stdin
From: Marcel Böhme <[email-masked]>
To: [email-masked]
Date: Sun, 27 Nov 2016 17:15:24 +0800
List-Id: <debbugs-submit.debbugs.gnu.org>

Dear all,

During fuzzing, we found one use-after-free in tac and one invalid-loading-of-value in tail.
Interestingly, these errors can be observed only when stdin is externally closed but internally expected to be open.

The bugs were found by AFLFast, a fork of AFL. 
The bug in tac was also found by Klee.
Thanks again also to Van-Thuan Pham.

The following execution crashes TAC in trunk. For the same execution of preinstalled version 8.21 on Ubuntu x86_64, valgrind flags a few invalid reads of size 8. There is no problem in version 6.10:

$ ./tac - - <&-
./tac: 'standard input': read error: Bad file descriptor
=================================================================
==53813==ERROR: AddressSanitizer: heap-use-after-free on address 0x61600000f990 at pc 0x00000040e127 bp 0x7ffefd0f76e0 sp 0x7ffefd0f76d8
READ of size 8 at 0x61600000f990 thread T0
    #0 0x40e126 in rpl_fseeko ../lib/fseeko.c:51
    #1 0x4032ac in temp_stream ../src/tac.c:480
    #2 0x4032ac in copy_to_temp ../src/tac.c:504
    #3 0x4032ac in tac_nonseekable ../src/tac.c:553
    #4 0x4032ac in tac_file ../src/tac.c:595
    #5 0x4032ac in main ../src/tac.c:701
    #6 0x7f135e464f44 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21f44)
    #7 0x404779  (/home/ubuntu/subjects/coreutils/obj-gcov/src/tac+0x404779)

0x61600000f990 is located 16 bytes inside of 568-byte region [0x61600000f980,0x61600000fbb8)
freed by thread T0 here:
    #0 0x7f135f5e1090 in __interceptor_free (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc2090)
    #1 0x7f135e4b0a24 in _IO_fclose (/lib/x86_64-linux-gnu/libc.so.6+0x6da24)

previously allocated by thread T0 here:
    #0 0x7f135f5e13a8 in __interceptor_malloc (/usr/lib/x86_64-linux-gnu/libasan.so.3+0xc23a8)
    #1 0x7f135e4b0c81 in fdopen (/lib/x86_64-linux-gnu/libc.so.6+0x6dc81)

SUMMARY: AddressSanitizer: heap-use-after-free ../lib/fseeko.c:51 in rpl_fseeko
=================================================================

The following execution of TAIL in trunk is flagged by UBSAN.
$ tail -f <&-
tail.c:2220:18: runtime error: load of value 190, which is not a valid value for type ‘_Bool'

For trunk version, version 8.21, and version 6.10 on Ubuntu x86_64, valgrind reports:
==28236== Conditional jump or move depends on uninitialised value(s)
==28236==    at 0x405941: ignore_fifo_and_pipe (tail.c:2220)
==28236==    by 0x405941: main (tail.c:2334)

Best regards,
- Marcel