is_ntfs_dotgit: use a size_t for traversing string

peff · peff · commit 11a9f4d807a0 · 2018-05-21T23:50:11.000-04:00
We walk through the "name" string using an int, which can
wrap to a negative value and cause us to read random memory
before our array (e.g., by creating a tree with a name &gt;2GB,
since "int" is still 32 bits even on most 64-bit platforms).
Worse, this is easy to trigger during the fsck_tree() check,
which is supposed to be protecting us from malicious
garbage.

Note one bit of trickiness in the existing code: we
sometimes assign -1 to "len" at the end of the loop, and
then rely on the "len++" in the for-loop's increment to take
it back to 0. This is still legal with a size_t, since
assigning -1 will turn into SIZE_MAX, which then wraps
around to 0 on increment.

Signed-off-by: Jeff King &lt;peff@peff.net&gt;
diff --git a/path.c b/path.c
@@ -1224,7 +1224,7 @@ static int only_spaces_and_periods(const char *path, size_t len, size_t skip)
 
 int is_ntfs_dotgit(const char *name)
 {
-	int len;
+	size_t len;
 
 	for (len = 0; ; len++)
 		if (!name[len] || name[len] == '\\' || is_dir_sep(name[len])) {

Original file line number	Diff line number	Diff line change
`@@ -1224,7 +1224,7 @@ static int only_spaces_and_periods(const char *path, size_t len, size_t skip)`
`1224`	`1224`
`1225`	`1225`	`int is_ntfs_dotgit(const char *name)`
`1226`	`1226`	`{`
`1227`		`- int len;`
	`1227`	`+ size_t len;`
`1228`	`1228`
`1229`	`1229`	`for (len = 0; ; len++)`
`1230`	`1230`	`if (!name[len] \|\| name[len] == '\\' \|\| is_dir_sep(name[len])) {`