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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.
libnfs-4.0.0-vitalif
Yann GASCUEL 2017-11-26 16:24:03 +01:00
parent a3b793342b
commit 53e3c86c58
2 changed files with 20 additions and 0 deletions
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5
README
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@ -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.

15
examples/ld_nfs.c
View File

@ -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)");