* [PATCH] diff: ensure correct lifetime of external_diff_cmd
@ 2019-01-09 22:10 Kim Gybels
2019-01-09 23:10 ` Eric Sunshine
2019-01-11 20:26 ` [PATCH v2] " Kim Gybels
0 siblings, 2 replies; 6+ messages in thread
From: Kim Gybels @ 2019-01-09 22:10 UTC (permalink / raw)
To: git
Cc: Junio C Hamano, Johannes Schindelin, Karsten Blees, Johannes Sixt,
Kim Gybels
According to getenv(3)'s notes:
The implementation of getenv() is not required to be reentrant. The
string pointed to by the return value of getenv() may be statically
allocated, and can be modified by a subsequent call to getenv(),
putenv(3), setenv(3), or unsetenv(3).
Since strings returned by getenv() are allowed to change on subsequent
calls to getenv(), make sure to duplicate when caching external_diff_cmd
from environment.
This problem becomes apparent on Git for Windows since fe21c6b285df
(mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)),
when the getenv() implementation provided in compat/mingw.c was changed
to keep a certain amount of alloc'ed strings and freeing them on
subsequent calls.
This fixes https://github.com/git-for-windows/git/issues/2007:
$ yes n | git -c difftool.prompt=yes difftool fe21c6b285df fe21c6b285df~100
Viewing (1/404): '.gitignore'
Launch 'bc3' [Y/n]?
Viewing (2/404): 'Documentation/.gitignore'
Launch 'bc3' [Y/n]?
Viewing (3/404): 'Documentation/Makefile'
Launch 'bc3' [Y/n]?
Viewing (4/404): 'Documentation/RelNotes/2.14.5.txt'
Launch 'bc3' [Y/n]?
Viewing (5/404): 'Documentation/RelNotes/2.15.3.txt'
Launch 'bc3' [Y/n]?
Viewing (6/404): 'Documentation/RelNotes/2.16.5.txt'
Launch 'bc3' [Y/n]?
Viewing (7/404): 'Documentation/RelNotes/2.17.2.txt'
Launch 'bc3' [Y/n]?
Viewing (8/404): 'Documentation/RelNotes/2.18.1.txt'
Launch 'bc3' [Y/n]?
Viewing (9/404): 'Documentation/RelNotes/2.19.0.txt'
Launch 'bc3' [Y/n]? error: cannot spawn ¦?: No such file or directory
fatal: external diff died, stopping at Documentation/RelNotes/2.19.1.txt
Signed-off-by: Kim Gybels <kgybels@infogroep.be>
---
diff.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/diff.c b/diff.c
index dc9965e836..f69687e288 100644
--- a/diff.c
+++ b/diff.c
@@ -492,6 +492,9 @@ static const char *external_diff(void)
external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
if (!external_diff_cmd)
external_diff_cmd = external_diff_cmd_cfg;
+ else
+ external_diff_cmd = xstrdup(external_diff_cmd);
+
done_preparing = 1;
return external_diff_cmd;
}
--
2.20.1.windows.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH] diff: ensure correct lifetime of external_diff_cmd
2019-01-09 22:10 [PATCH] diff: ensure correct lifetime of external_diff_cmd Kim Gybels
@ 2019-01-09 23:10 ` Eric Sunshine
2019-01-10 15:47 ` Johannes Schindelin
2019-01-10 18:27 ` Junio C Hamano
2019-01-11 20:26 ` [PATCH v2] " Kim Gybels
1 sibling, 2 replies; 6+ messages in thread
From: Eric Sunshine @ 2019-01-09 23:10 UTC (permalink / raw)
To: Kim Gybels
Cc: Git List, Junio C Hamano, Johannes Schindelin, Karsten Blees,
Johannes Sixt
On Wed, Jan 9, 2019 at 5:19 PM Kim Gybels <kgybels@infogroep.be> wrote:
> According to getenv(3)'s notes:
> [...]
> Since strings returned by getenv() are allowed to change on subsequent
> calls to getenv(), make sure to duplicate when caching external_diff_cmd
> from environment.
> [...]
> Signed-off-by: Kim Gybels <kgybels@infogroep.be>
> ---
> diff --git a/diff.c b/diff.c
> @@ -492,6 +492,9 @@ static const char *external_diff(void)
> external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
> if (!external_diff_cmd)
> external_diff_cmd = external_diff_cmd_cfg;
> + else
> + external_diff_cmd = xstrdup(external_diff_cmd);
Make sense.
Not shown in the context is that 'external_diff_cmd' is static, so
this is not (in the traditional sense) leaking the dup'd string.
I do find that the logic is obscured by doing the xstrdup() in the
'else' arm; it would be easier to grok if the condition was reversed
and xstrdup() done in the 'then' arm.
However, you might also consider using xstrdup_or_null(), like this:
external_diff_cmd = xstrdup_or_null(getenv(...));
if (!external_diff_cmd)
...as before...
> done_preparing = 1;
> return external_diff_cmd;
> }
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] diff: ensure correct lifetime of external_diff_cmd
2019-01-09 23:10 ` Eric Sunshine
@ 2019-01-10 15:47 ` Johannes Schindelin
2019-01-10 18:27 ` Junio C Hamano
1 sibling, 0 replies; 6+ messages in thread
From: Johannes Schindelin @ 2019-01-10 15:47 UTC (permalink / raw)
To: Eric Sunshine
Cc: Kim Gybels, Git List, Junio C Hamano, Karsten Blees,
Johannes Sixt
Hi,
On Wed, 9 Jan 2019, Eric Sunshine wrote:
> On Wed, Jan 9, 2019 at 5:19 PM Kim Gybels <kgybels@infogroep.be> wrote:
> > According to getenv(3)'s notes:
> > [...]
> > Since strings returned by getenv() are allowed to change on subsequent
> > calls to getenv(), make sure to duplicate when caching external_diff_cmd
> > from environment.
> > [...]
> > Signed-off-by: Kim Gybels <kgybels@infogroep.be>
> > ---
> > diff --git a/diff.c b/diff.c
> > @@ -492,6 +492,9 @@ static const char *external_diff(void)
> > external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
> > if (!external_diff_cmd)
> > external_diff_cmd = external_diff_cmd_cfg;
> > + else
> > + external_diff_cmd = xstrdup(external_diff_cmd);
>
> Make sense.
>
> Not shown in the context is that 'external_diff_cmd' is static, so
> this is not (in the traditional sense) leaking the dup'd string.
Ah! And that also explains why we do not need to take care of releasing
the memory via `free()` (which is what I was wondering about).
> I do find that the logic is obscured by doing the xstrdup() in the
> 'else' arm; it would be easier to grok if the condition was reversed and
> xstrdup() done in the 'then' arm.
>
> However, you might also consider using xstrdup_or_null(), like this:
>
> external_diff_cmd = xstrdup_or_null(getenv(...));
> if (!external_diff_cmd)
> ...as before...
>
> > done_preparing = 1;
> > return external_diff_cmd;
> > }
I like this version slightly better, too.
Thanks for diagnosing and fixing this annoying bug!
Dscho
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH] diff: ensure correct lifetime of external_diff_cmd
2019-01-09 23:10 ` Eric Sunshine
2019-01-10 15:47 ` Johannes Schindelin
@ 2019-01-10 18:27 ` Junio C Hamano
1 sibling, 0 replies; 6+ messages in thread
From: Junio C Hamano @ 2019-01-10 18:27 UTC (permalink / raw)
To: Eric Sunshine
Cc: Kim Gybels, Git List, Johannes Schindelin, Karsten Blees,
Johannes Sixt
Eric Sunshine <sunshine@sunshineco.com> writes:
> However, you might also consider using xstrdup_or_null(), like this:
>
> external_diff_cmd = xstrdup_or_null(getenv(...));
> if (!external_diff_cmd)
> ...as before...
>
>> done_preparing = 1;
>> return external_diff_cmd;
>> }
Looks good.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2] diff: ensure correct lifetime of external_diff_cmd
2019-01-09 22:10 [PATCH] diff: ensure correct lifetime of external_diff_cmd Kim Gybels
2019-01-09 23:10 ` Eric Sunshine
@ 2019-01-11 20:26 ` Kim Gybels
2019-01-12 2:44 ` Junio C Hamano
1 sibling, 1 reply; 6+ messages in thread
From: Kim Gybels @ 2019-01-11 20:26 UTC (permalink / raw)
To: git
Cc: Eric Sunshine, Junio C Hamano, Johannes Schindelin, Karsten Blees,
Johannes Sixt, Kim Gybels
According to getenv(3)'s notes:
The implementation of getenv() is not required to be reentrant. The
string pointed to by the return value of getenv() may be statically
allocated, and can be modified by a subsequent call to getenv(),
putenv(3), setenv(3), or unsetenv(3).
Since strings returned by getenv() are allowed to change on subsequent
calls to getenv(), make sure to duplicate when caching external_diff_cmd
from environment.
This problem becomes apparent on Git for Windows since fe21c6b285df
(mingw: reencode environment variables on the fly (UTF-16 <-> UTF-8)),
when the getenv() implementation provided in compat/mingw.c was changed
to keep a certain amount of alloc'ed strings and freeing them on
subsequent calls.
This fixes https://github.com/git-for-windows/git/issues/2007:
$ yes n | git -c difftool.prompt=yes difftool fe21c6b285df fe21c6b285df~100
Viewing (1/404): '.gitignore'
Launch 'bc3' [Y/n]?
Viewing (2/404): 'Documentation/.gitignore'
Launch 'bc3' [Y/n]?
Viewing (3/404): 'Documentation/Makefile'
Launch 'bc3' [Y/n]?
Viewing (4/404): 'Documentation/RelNotes/2.14.5.txt'
Launch 'bc3' [Y/n]?
Viewing (5/404): 'Documentation/RelNotes/2.15.3.txt'
Launch 'bc3' [Y/n]?
Viewing (6/404): 'Documentation/RelNotes/2.16.5.txt'
Launch 'bc3' [Y/n]?
Viewing (7/404): 'Documentation/RelNotes/2.17.2.txt'
Launch 'bc3' [Y/n]?
Viewing (8/404): 'Documentation/RelNotes/2.18.1.txt'
Launch 'bc3' [Y/n]?
Viewing (9/404): 'Documentation/RelNotes/2.19.0.txt'
Launch 'bc3' [Y/n]? error: cannot spawn ¦?: No such file or directory
fatal: external diff died, stopping at Documentation/RelNotes/2.19.1.txt
Signed-off-by: Kim Gybels <kgybels@infogroep.be>
---
Uses xstrdup_or_null as suggested by Eric Sunshine.
diff.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/diff.c b/diff.c
index dc9965e836..5634992bbc 100644
--- a/diff.c
+++ b/diff.c
@@ -487,11 +487,11 @@ static const char *external_diff(void)
static const char *external_diff_cmd = NULL;
static int done_preparing = 0;
if (done_preparing)
return external_diff_cmd;
- external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
+ external_diff_cmd = xstrdup_or_null(getenv("GIT_EXTERNAL_DIFF"));
if (!external_diff_cmd)
external_diff_cmd = external_diff_cmd_cfg;
done_preparing = 1;
return external_diff_cmd;
}
--
2.20.1.windows.1
^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2] diff: ensure correct lifetime of external_diff_cmd
2019-01-11 20:26 ` [PATCH v2] " Kim Gybels
@ 2019-01-12 2:44 ` Junio C Hamano
0 siblings, 0 replies; 6+ messages in thread
From: Junio C Hamano @ 2019-01-12 2:44 UTC (permalink / raw)
To: Kim Gybels
Cc: git, Eric Sunshine, Johannes Schindelin, Karsten Blees,
Johannes Sixt
Kim Gybels <kgybels@infogroep.be> writes:
> According to getenv(3)'s notes:
>
> The implementation of getenv() is not required to be reentrant. The
> string pointed to by the return value of getenv() may be statically
> allocated, and can be modified by a subsequent call to getenv(),
> putenv(3), setenv(3), or unsetenv(3).
> ...
> Signed-off-by: Kim Gybels <kgybels@infogroep.be>
> ---
Thanks, looking good.
Will queue.
>
> Uses xstrdup_or_null as suggested by Eric Sunshine.
>
> diff.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/diff.c b/diff.c
> index dc9965e836..5634992bbc 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -487,11 +487,11 @@ static const char *external_diff(void)
> static const char *external_diff_cmd = NULL;
> static int done_preparing = 0;
>
> if (done_preparing)
> return external_diff_cmd;
> - external_diff_cmd = getenv("GIT_EXTERNAL_DIFF");
> + external_diff_cmd = xstrdup_or_null(getenv("GIT_EXTERNAL_DIFF"));
> if (!external_diff_cmd)
> external_diff_cmd = external_diff_cmd_cfg;
> done_preparing = 1;
> return external_diff_cmd;
> }
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2019-01-12 2:44 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-01-09 22:10 [PATCH] diff: ensure correct lifetime of external_diff_cmd Kim Gybels
2019-01-09 23:10 ` Eric Sunshine
2019-01-10 15:47 ` Johannes Schindelin
2019-01-10 18:27 ` Junio C Hamano
2019-01-11 20:26 ` [PATCH v2] " Kim Gybels
2019-01-12 2:44 ` Junio C Hamano
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).