config.c: avoid integer truncation in `copy_or_rename_section_in_file()`

There are a couple of spots within `copy_or_rename_section_in_file()`
that incorrectly use an `int` to track an offset within a string, which
may truncate or wrap around to a negative value.

Historically it was impossible to have a line longer than 1024 bytes
anyway, since we used fgets() with a fixed-size buffer of exactly that
length. But the recent change to use a strbuf permits us to read lines
of arbitrary length, so it's possible for a malicious input to cause us
to overflow past INT_MAX and do an out-of-bounds array read.

Practically speaking, however, this should never happen, since it
requires 2GB section names or values, which are unrealistic in
non-malicious circumstances.

Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>

diff --git a/config.c b/config.c
index 524347676d0da03b76bbe74bebf7078cf7c0d368..e4189aa2d79f628bfe2a2ab673be5e0c20463505 100644 (file)
--- a/config.c
+++ b/config.c
@@ -3027,9 +3027,10 @@ void git_config_set_multivar(const char *key, const char *value,
                                        flags);
 }
 
-static int section_name_match (const char *buf, const char *name)
+static size_t section_name_match (const char *buf, const char *name)
 {
-       int i = 0, j = 0, dot = 0;
+       size_t i = 0, j = 0;
+       int dot = 0;
        if (buf[i] != '[')
                return 0;
        for (i = 1; buf[i] && buf[i] != ']'; i++) {
@@ -3133,15 +3134,14 @@ static int git_config_copy_or_rename_section_in_file(const char *config_filename
        }
 
        while (!strbuf_getwholeline(&buf, config_file, '\n')) {
-               unsigned i;
-               int length;
+               size_t i, length;
                int is_section = 0;
                char *output = buf.buf;
                for (i = 0; buf.buf[i] && isspace(buf.buf[i]); i++)
                        ; /* do nothing */
                if (buf.buf[i] == '[') {
                        /* it's a section */
-                       int offset;
+                       size_t offset;
                        is_section = 1;
 
                        /*