[PATCH] unleak paths allocated in "diff --no-index"
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Sep 2, 2022, 21:27 UTC
- Message-ID
- <xmqqilm579hc.fsf@gitster.g>
"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> ---
* Because we never pass NULL to the new helper, !path check is not strictly necessary, but it is conventional for free()-like functions to take NULL and safely become a no-op.
diff-no-index.c | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-)
diff --git c/diff-no-index.c w/diff-no-index.c index 9a8b09346b..2770b7d15a 100644 --- c/diff-no-index.c +++ w/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 || + (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); paths[i] = p; } @@ -294,13 +306,18 @@ 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); + free_allocated_path(paths[0]); + free_allocated_path(paths[1]); /* * The return code for --no-index imitates diff(1):