From: Roy Marples <roy@marples.name>
Date: Sat, 20 Jun 2026 08:49:44 +0000 (+0100)
Subject: privsep: ps_root_readfile should return the real file size
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=HEAD;p=thirdparty%2Fdhcpcd.git

privsep: ps_root_readfile should return the real file size

readfile NUL terminates the buffer to make things easy.
We need to transmit this over IPC just ensure the receiver has
a big enough buffer, again to make things easy.
So on success, we need to trim the NUL from the returned length
so the actual file size is accurate.
---

diff --git a/src/common.c b/src/common.c
index 953db6f6..1cb2f26b 100644
--- a/src/common.c
+++ b/src/common.c
@@ -124,6 +124,10 @@ readfile(const char *file, void **data, size_t *len)
 		return -1;
 	if (fstat(fd, &st) == -1)
 		goto out;
+
+	/* Ensure that what we read is NUL terminated
+	 * because it's mainly text files and this just
+	 * makes it easier. */
 	nlen = (size_t)st.st_size + 1;
 	if (nlen > *len) {
 		void *ndata = realloc(*data, nlen);
@@ -132,14 +136,15 @@ readfile(const char *file, void **data, size_t *len)
 		*data = ndata;
 		*len = nlen;
 	}
-	bytes = read(fd, *data, *len);
+	bytes = read(fd, *data, *len - 1);
+
 out:
 	close(fd);
 	if (bytes == -1)
 		return -1;
 	buf = *data;
 	buf[bytes] = '\0';
-	return bytes + 1;
+	return bytes;
 }
 
 ssize_t
diff --git a/src/privsep-root.c b/src/privsep-root.c
index 70bad9c3..798076f2 100644
--- a/src/privsep-root.c
+++ b/src/privsep-root.c
@@ -529,7 +529,10 @@ ps_root_recvmsgcb(void *arg, struct ps_msghdr *psm, struct msghdr *msg)
 		err = readfile(data, &ctx->ps_buf, &ctx->ps_buflen);
 		if (err != -1) {
 			rdata = ctx->ps_buf;
-			rlen = (size_t)err;
+			/* We know the buffer is NUL terminated.
+			 * Send it over IPC to ensure the receiver has
+			 * enough space for it as well. */
+			rlen = (size_t)err + 1;
 		}
 		break;
 	case PS_WRITEFILE:
@@ -1040,11 +1043,18 @@ ssize_t
 ps_root_readfile(struct dhcpcd_ctx *ctx, const char *file, void **data,
     size_t *len)
 {
+	ssize_t err;
+
 	if (ps_sendcmd(ctx, PS_ROOT_FD(ctx), PS_READFILE, 0, file,
 		strlen(file) + 1) == -1)
 		return -1;
 
-	return ps_root_mreaderror(ctx, data, len);
+	err = ps_root_mreaderror(ctx, data, len);
+	if (err == -1)
+		return -1;
+
+	/* The returned length should not include the NUL terminator */
+	return err - 1;
 }
 
 ssize_t