From 53e3c86c58e460b5ebbb6d66c97371a8238685d1 Mon Sep 17 00:00:00 2001
From: Yann GASCUEL <34003959+lnv42@users.noreply.github.com>
Date: Sun, 26 Nov 2017 16:24:03 +0100
Subject: [PATCH] examples/ld_nfs.c: feature: faking uid and gid

add the possiblity of faking the uid and the gid in the nfs context.
uid and gid value are read from env variables LD_NFS_UID and LD_NFS_GID.
This can be useful on "insecure" enabled NFS share to make the server
trust you as a root.

Few lines added to the README to document the feature.
---
 README            |  5 +++++
 examples/ld_nfs.c | 15 +++++++++++++++
 2 files changed, 20 insertions(+)

diff --git a/README b/README
index e38890d..cbf1d3d 100644
--- a/README
+++ b/README
@@ -151,6 +151,11 @@ LD_NFS_DEBUG=9 LD_PRELOAD=./ld_nfs.so cat nfs://127.0.0.1/data/tmp/foo123
 
 LD_NFS_DEBUG=9 LD_PRELOAD=./ld_nfs.so cp nfs://127.0.0.1/data/tmp/foo123 nfs://127.0.0.1/data/tmp/foo123.copy
 
+LD_NFS_UID and LD_NFS_GID can be used to fake the uid andthe gid in the nfs context.
+This can be useful on "insecure" enabled NFS share to make the server trust you as a root.
+You can try to run as a normal user things like :
+LD_NFS_DEBUG=9 LD_NFS_UID=0 LD_NFS_GID=0 LD_PRELOAD=./ld_nfs.so chown root:root nfs://127.0.0.1/data/tmp/foo123
+
 This is just a toy preload module. Don't open bugs if it does not work. Send
 patches to make it better instead.
 
diff --git a/examples/ld_nfs.c b/examples/ld_nfs.c
index 05e0f40..5003342 100644
--- a/examples/ld_nfs.c
+++ b/examples/ld_nfs.c
@@ -34,6 +34,8 @@
 #define NFS_MAX_FD  255
 
 static int debug = 0;
+static int nfsuid = -1;
+static int nfsgid = -1;
 
 #ifndef discard_const
 #define discard_const(ptr) ((void *)((intptr_t)(ptr)))
@@ -79,6 +81,11 @@ int open(const char *path, int flags, mode_t mode)
 			return -1;
 		}
 
+		if (nfsuid >= 0)
+			nfs_set_uid(nfs, nfsuid);
+		if (nfsgid >= 0)
+			nfs_set_gid(nfs, nfsgid);
+
 		url = nfs_parse_url_full(nfs, path);
 		if (url == NULL) {
 			LD_NFS_DPRINTF(1, "Failed to parse URL: %s\n",
@@ -675,6 +682,14 @@ static void __attribute__((constructor)) _init(void)
 		debug = atoi(getenv("LD_NFS_DEBUG"));
 	}
 
+	if (getenv("LD_NFS_UID") != NULL) {
+		nfsuid = atoi(getenv("LD_NFS_UID"));
+	}
+
+	if (getenv("LD_NFS_GID") != NULL) {
+		nfsgid = atoi(getenv("LD_NFS_GID"));
+	}
+
 	real_open = dlsym(RTLD_NEXT, "open");
 	if (real_open == NULL) {
 		LD_NFS_DPRINTF(0, "Failed to dlsym(open)");