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From a08eabc6e5a3e0a9c7a15ca15ff7d450ecb6db88 Mon Sep 17 00:00:00 2001
From: Jan Engelhardt <jengelh@inai.de>
Date: Tue, 12 Oct 2021 17:32:43 +0200
Subject: [PATCH] io: fix a use-after-free in conjunction with HX_realpath
HX_readlink(&x, ...) forgot to set x to nullptr upon error, which
trips up subsequent calls to HX_readlink with the very same x.
Fixes: v3.26-1-g97f4be2
---
src/io.c | 8 ++++++--
src/tc-realpath.c | 10 ++++++++++
2 files changed, 16 insertions(+), 2 deletions(-)
diff --git a/src/io.c b/src/io.c
index 95d6fd6..14078fc 100644
--- a/src/io.c
+++ b/src/io.c
@@ -316,8 +316,10 @@ EXPORT_SYMBOL int HX_readlink(hxmc_t **target, const char *path)
ssize_t ret = readlink(path, *target, linkbuf_size);
if (ret < 0) {
int saved_errno = errno;
- if (allocate)
+ if (allocate) {
HXmc_free(*target);
+ *target = nullptr;
+ }
return -(errno = saved_errno);
}
if (static_cast(size_t, ret) < linkbuf_size) {
@@ -327,8 +329,10 @@ EXPORT_SYMBOL int HX_readlink(hxmc_t **target, const char *path)
linkbuf_size *= 2;
if (HXmc_setlen(target, linkbuf_size) == NULL) {
int saved_errno = errno;
- if (allocate)
+ if (allocate) {
HXmc_free(*target);
+ *target = nullptr;
+ }
return -(errno = saved_errno);
}
}
diff --git a/src/tc-realpath.c b/src/tc-realpath.c
index 5dd9aa2..c2ef15a 100644
--- a/src/tc-realpath.c
+++ b/src/tc-realpath.c
@@ -11,6 +11,7 @@
#include <stdlib.h>
#include <libHX/io.h>
#include <libHX/option.h>
+#include <libHX/string.h>
static unsigned int rp_flags;
static unsigned int rp_absolute;
@@ -42,6 +43,14 @@ static bool rp_get_options(int *argc, const char ***argv)
return true;
}
+static void t_1(void)
+{
+ hxmc_t *tmp = HXmc_strinit("");
+ /* two components, so that HX_readlink gets called twice */
+ HX_realpath(&tmp, "/dev/tty", HX_REALPATH_DEFAULT);
+ HXmc_free(tmp);
+}
+
int main(int argc, const char **argv)
{
hxmc_t *res;
@@ -49,6 +58,7 @@ int main(int argc, const char **argv)
if (!rp_get_options(&argc, &argv))
return EXIT_FAILURE;
+ t_1();
res = NULL;
while (--argc > 0) {
--
2.33.0
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