Re: [PATCH v2] diff --no-index: unleak paths[] elements
Am 03.09.22 um 01:49 schrieb Junio C Hamano:
Show 57 quoted lines
> "git diff --no-index" codepath starts with the two elements in
> argv[] and munges them into two paths to be compared, stored in a
> separate path[] arrays. The munging is implemented in a rather
> haphazard way, sometimes overwriting old version with a new copy,
> and sometimes a constant string assigned to path[], making it
> impossible to release the resources properly:
>
> * A single dash "-" from the command line is a special signal that
> the standard input is used for the side to be compared, and is
> internally replaced with a copy of string "-" at a known address.
>
> * When run in a subdirectory, full paths to the two paths are
> allocated and placed in path[].
>
> * After the above happens, when comparing a file with a directory,
> the directory side is replaced with the path to a file in the
> directory with the same name as the file.
>
> This was perfectly fine for just two strings that are pathnames used
> during the lifetime of the program and cleaned up upon program exit,
> but it gets in the way when leak sanitizer is in effect. The third
> step can be losing the full path that was allocated in the second
> step, but it is not easy to tell if its input is an allocated piece
> of memory to begin with.
>
> Loosen the earlier two steps a bit so that elements of the path[]
> array that come to the directory/file comparison code are either the
> singleton "-" or an allocated piece of memory. Use that knowledge
> in the third step to release an allocated piece of memory when it
> replaces the path to a directory with the path to a file in that
> directory, and also at the end to release the two elements of the
> path[] array as needed.
>
> Signed-off-by: Junio C Hamano <gitster@pobox.com>
> ---
>
> * The previous one allowed strbuf_release() to free replacement.buf
> which may be used in path[0] or path[1] potentially leading to
> double freeing. The kosher way may be to use strbuf_detach() in
> fixup_paths(), but this is a simpler fix, it is getting late in
> the day, and I am getting sick of fighting the leak-checker, so...
>
> diff-no-index.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
>
> diff --git a/diff-no-index.c b/diff-no-index.c
> index 9a8b09346b..77a126469b 100644
> --- a/diff-no-index.c
> +++ b/diff-no-index.c
> @@ -208,6 +208,14 @@ static void append_basename(struct strbuf *path, const char *dir, const char *fi
> strbuf_addstr(path, tail ? tail + 1 : file);
> }
>
> +static void free_allocated_path(const char *path)
> +{
> + if (!path ||How can path be NULL? And if it was, why shield free(3) from it?
Show 26 quoted lines
> + (path == file_from_standard_input))
> + return;
> + free((char *)path);
> +}
> +
> /*
> * DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F"
> * Note that we append the basename of F to D/, so "diff a/b/file D"
> @@ -226,9 +234,11 @@ static void fixup_paths(const char **path, struct strbuf *replacement)
> return;
> if (isdir0) {
> append_basename(replacement, path[0], path[1]);
> + free_allocated_path(path[0]);
> path[0] = replacement->buf;
> } else {
> append_basename(replacement, path[1], path[0]);
> + free_allocated_path(path[1]);
> path[1] = replacement->buf;
> }
> }
> @@ -274,6 +284,8 @@ int diff_no_index(struct rev_info *revs,
> p = file_from_standard_input;
> else if (prefix)
> p = prefix_filename(prefix, p);
> + else
> + p = xstrdup(p);prefix_filename(NULL, p) is basically the same as xstrdup(p), so those two conditional branches could be joined.
Show 27 quoted lines
> paths[i] = p;
> }
>
> @@ -294,13 +306,21 @@ int diff_no_index(struct rev_info *revs,
> setup_diff_pager(&revs->diffopt);
> revs->diffopt.flags.exit_with_status = 1;
>
> - if (queue_diff(&revs->diffopt, paths[0], paths[1]))
> + if (queue_diff(&revs->diffopt, paths[0], paths[1])) {
> + free_allocated_path(paths[0]);
> + free_allocated_path(paths[1]);
> return 1;
> + }
> diff_set_mnemonic_prefix(&revs->diffopt, "1/", "2/");
> diffcore_std(&revs->diffopt);
> diff_flush(&revs->diffopt);
>
> - strbuf_release(&replacement);
> + /*
> + * do not strbuf_release(&replacement), as it is in paths[]
> + * when replacement was actually used.
> + */
> + free_allocated_path(paths[0]);
> + free_allocated_path(paths[1]);
>
> /*
> * The return code for --no-index imitates diff(1):Perhaps avoid the need for that comment by moving that strbuf to where it's used and have it spend its full lifecycle there? Something like:
---
diff-no-index.c | 50 ++++++++++++++++++++++---------------------------
1 file changed, 22 insertions(+), 28 deletions(-)
Show changes to diff-no-index.c +22 −29
diff --git a/diff-no-index.c b/diff-no-index.c
index 77a126469b..9f8b78f173 100644
--- a/diff-no-index.c
+++ b/diff-no-index.c
@@ -196,18 +196,6 @@ static int queue_diff(struct diff_options *o,
}
}
-/* append basename of F to D */
-static void append_basename(struct strbuf *path, const char *dir, const char *file)
-{
- const char *tail = strrchr(file, '/');
-
- strbuf_addstr(path, dir);
- while (path->len && path->buf[path->len - 1] == '/')
- path->len--;
- strbuf_addch(path, '/');
- strbuf_addstr(path, tail ? tail + 1 : file);
-}
-
static void free_allocated_path(const char *path)
{
if (!path ||
@@ -216,12 +204,28 @@ static void free_allocated_path(const char *path)
free((char *)path);
}
+/* append basename of F to D */
+static void append_basename(const char **dir, const char *file)
+{
+ const char *tail = strrchr(file, '/');
+ struct strbuf path = STRBUF_INIT;
+
+ strbuf_addstr(&path, *dir);
+ while (path.len && path.buf[path.len - 1] == '/')
+ path.len--;
+ strbuf_addch(&path, '/');
+ strbuf_addstr(&path, tail ? tail + 1 : file);
+
+ free_allocated_path(*dir);
+ *dir = strbuf_detach(&path, NULL);
+}
+
/*
* DWIM "diff D F" into "diff D/F F" and "diff F D" into "diff F D/F"
* Note that we append the basename of F to D/, so "diff a/b/file D"
* becomes "diff a/b/file D/file", not "diff a/b/file D/a/b/file".
*/
-static void fixup_paths(const char **path, struct strbuf *replacement)
+static void fixup_paths(const char **path)
{
unsigned int isdir0, isdir1;
@@ -232,15 +236,10 @@ static void fixup_paths(const char **path, struct strbuf *replacement)
isdir1 = is_directory(path[1]);
if (isdir0 == isdir1)
return;
- if (isdir0) {
- append_basename(replacement, path[0], path[1]);
- free_allocated_path(path[0]);
- path[0] = replacement->buf;
- } else {
- append_basename(replacement, path[1], path[0]);
- free_allocated_path(path[1]);
- path[1] = replacement->buf;
- }
+ if (isdir0)
+ append_basename(&path[0], path[1]);
+ else
+ append_basename(&path[1], path[0]);
}
static const char * const diff_no_index_usage[] = {
@@ -254,7 +253,6 @@ int diff_no_index(struct rev_info *revs,
{
int i, no_index;
const char *paths[2];
- struct strbuf replacement = STRBUF_INIT;
const char *prefix = revs->prefix;
struct option no_index_options[] = {
OPT_BOOL_F(0, "no-index", &no_index, "",
@@ -289,7 +287,7 @@ int diff_no_index(struct rev_info *revs,
paths[i] = p;
}
- fixup_paths(paths, &replacement);
+ fixup_paths(paths);
revs->diffopt.skip_stat_unmatch = 1;
if (!revs->diffopt.output_format)
@@ -315,10 +313,6 @@ int diff_no_index(struct rev_info *revs,
diffcore_std(&revs->diffopt);
diff_flush(&revs->diffopt);
- /*
- * do not strbuf_release(&replacement), as it is in paths[]
- * when replacement was actually used.
- */
free_allocated_path(paths[0]);
free_allocated_path(paths[1]);
--
2.37.2
Junio C Hamano
