strbuf_readlink(): avoid calling readlink() twice in corner-cases

The `strbuf_readlink()` function calls `readlink()`` twice if the hint
argument specifies the exact size of the link target (e.g. by passing
stat.st_size as returned by `lstat()`). This is necessary because
`readlink(..., hint) == hint` could mean that the buffer was too small.

Use `hint + 1` as buffer size to prevent this.

Signed-off-by: Karsten Blees <karsten.blees@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Karsten Blees 2026-01-09 20:05:07 +00:00 committed by Junio C Hamano
parent 7997e36561
commit 0fcbb57f97

View File

@ -578,12 +578,12 @@ int strbuf_readlink(struct strbuf *sb, const char *path, size_t hint)
while (hint < STRBUF_MAXLINK) {
ssize_t len;
strbuf_grow(sb, hint);
len = readlink(path, sb->buf, hint);
strbuf_grow(sb, hint + 1);
len = readlink(path, sb->buf, hint + 1);
if (len < 0) {
if (errno != ERANGE)
break;
} else if (len < hint) {
} else if (len <= hint) {
strbuf_setlen(sb, len);
return 0;
}