Re: "git branch HEAD" dumps core when on detached head (NULL pointer dereference)

[Duy Nguyen]

On Thu, Feb 21, 2013 at 8:24 PM, Per Cederqvist  wrote:
> Sorry, but isolating the issue reporting it here is about as much time
> as I can spend on this issue. Learning the coding standard of Git and
> how to write test cases is not something I'm prepared to do, at least
> not at the moment. I hope there is a place for users and reporters of
> bugs in the Git community.

Sure. No problem. I just thought you might want to finish it off. I'll
look into it.
-- 
Duy
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Re: "git branch HEAD" dumps core when on detached head (NULL pointer dereference)

[Per Cederqvist]

On 02/21/13 13:50, Duy Nguyen wrote:

On Thu, Feb 21, 2013 at 7:27 PM, Per Cederqvist  wrote:

Running "git branch HEAD" may be a stupid thing to do. It actually
was a mistake on my part. Still, I don't think git should dereference
a NULL pointer.


We should not. Can you make a patch to fix it (with test cases)? You
may want to fix the two preceding blocks, "if (new_upstream)" and "if
(unset_upstream)", as well. They don't check for NULL branch either. I
think we can say something like "detached HEAD is not valid for this
operation" before exit.


Sorry, but isolating the issue reporting it here is about as much time
as I can spend on this issue. Learning the coding standard of Git and
how to write test cases is not something I'm prepared to do, at least
not at the moment. I hope there is a place for users and reporters of
bugs in the Git community.

/ceder



Tested using git 1.8.1.4 adn 1.8.1.1.

Repeat by:

 mkdir branchcrash || exit 1
 cd branchcrash
 git init
 touch a; git add a; git commit -m"Added a".
 touch b; git add b; git commit -m"Added b".
 git checkout HEAD^
 git branch HEAD

The last command dumps core.  gdb session:

gdb /usr/local/bin/git core
GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
Copyright (C) 2012 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later

This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
For bug reporting instructions, please see:
...
Reading symbols from /usr/local/bin/git...done.
[New LWP 7174]

warning: Can't read pathname for load map: Input/output error.
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `git branch HEAD'.
Program terminated with signal 11, Segmentation fault.
#0  cmd_branch (argc=1, argv=0x7fffe6e2a0f0, prefix=)
 at builtin/branch.c:919
919 strbuf_addf(&buf, "refs/remotes/%s", branch->name);
(gdb) bt
#0  cmd_branch (argc=1, argv=0x7fffe6e2a0f0, prefix=)
 at builtin/branch.c:919
#1  0x004046ac in run_builtin (argv=0x7fffe6e2a0f0, argc=2,
 p=) at git.c:273
#2  handle_internal_command (argc=2, argv=0x7fffe6e2a0f0) at git.c:434
#3  0x00404df3 in run_argv (argv=0x7fffe6e29f90,
argcp=0x7fffe6e29f9c)
 at git.c:480
#4  main (argc=2, argv=0x7fffe6e2a0f0) at git.c:555
(gdb) p branch
$1 = (struct branch *) 0x0
(gdb) quit

 /ceder
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Re: "git branch HEAD" dumps core when on detached head (NULL pointer dereference)

[Duy Nguyen]

On Thu, Feb 21, 2013 at 7:27 PM, Per Cederqvist  wrote:
> Running "git branch HEAD" may be a stupid thing to do. It actually
> was a mistake on my part. Still, I don't think git should dereference
> a NULL pointer.

We should not. Can you make a patch to fix it (with test cases)? You
may want to fix the two preceding blocks, "if (new_upstream)" and "if
(unset_upstream)", as well. They don't check for NULL branch either. I
think we can say something like "detached HEAD is not valid for this
operation" before exit.

>
> Tested using git 1.8.1.4 adn 1.8.1.1.
>
> Repeat by:
>
> mkdir branchcrash || exit 1
> cd branchcrash
> git init
> touch a; git add a; git commit -m"Added a".
> touch b; git add b; git commit -m"Added b".
> git checkout HEAD^
> git branch HEAD
>
> The last command dumps core.  gdb session:
>
> gdb /usr/local/bin/git core
> GNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04
> Copyright (C) 2012 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later
> 
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "x86_64-linux-gnu".
> For bug reporting instructions, please see:
> ...
> Reading symbols from /usr/local/bin/git...done.
> [New LWP 7174]
>
> warning: Can't read pathname for load map: Input/output error.
> [Thread debugging using libthread_db enabled]
> Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
> Core was generated by `git branch HEAD'.
> Program terminated with signal 11, Segmentation fault.
> #0  cmd_branch (argc=1, argv=0x7fffe6e2a0f0, prefix=)
> at builtin/branch.c:919
> 919 strbuf_addf(&buf, "refs/remotes/%s", branch->name);
> (gdb) bt
> #0  cmd_branch (argc=1, argv=0x7fffe6e2a0f0, prefix=)
> at builtin/branch.c:919
> #1  0x004046ac in run_builtin (argv=0x7fffe6e2a0f0, argc=2,
> p=) at git.c:273
> #2  handle_internal_command (argc=2, argv=0x7fffe6e2a0f0) at git.c:434
> #3  0x00404df3 in run_argv (argv=0x7fffe6e29f90,
> argcp=0x7fffe6e29f9c)
> at git.c:480
> #4  main (argc=2, argv=0x7fffe6e2a0f0) at git.c:555
> (gdb) p branch
> $1 = (struct branch *) 0x0
> (gdb) quit
>
> /ceder
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> To unsubscribe from this list: send the line "unsubscribe git" in
> the body of a message to majord...@vger.kernel.org
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-- 
Duy
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