From: Vivek Goyal <vgoyal@redhat.com>

Date: Mon, 27 Jan 2020 19:01:12 +0000

Subject: [PATCH] virtiofsd: passthrough_ll: create new files in caller's

 context

We need to create files in the caller's context. Otherwise after

creating a file, the caller might not be able to do file operations on

that file.

Changed effective uid/gid to caller's uid/gid, create file and then

switch back to uid/gid 0.

Use syscall(setresuid, ...) otherwise glibc does some magic to change EUID

in all threads, which is not what we want.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

(cherry picked from commit 929cfb7a9a1b101cdfc9ac19807ecab4c81a13e4)

---

 tools/virtiofsd/passthrough_ll.c | 96 ++++++++++++++++++++++++++++++--

 1 file changed, 91 insertions(+), 5 deletions(-)

diff --git a/tools/virtiofsd/passthrough_ll.c b/tools/virtiofsd/passthrough_ll.c

index cd27c09f59..5e061797d4 100644

--- a/tools/virtiofsd/passthrough_ll.c

+++ b/tools/virtiofsd/passthrough_ll.c

@@ -50,6 +50,7 @@

 #include <stdlib.h>

 #include <string.h>

 #include <sys/file.h>

+#include <sys/syscall.h>

 #include <sys/xattr.h>

 #include <unistd.h>

@@ -83,6 +84,11 @@ struct lo_inode {

     uint64_t refcount; /* protected by lo->mutex */

 };

+struct lo_cred {

+    uid_t euid;

+    gid_t egid;

+};

+

 enum {

     CACHE_NEVER,

     CACHE_NORMAL,

@@ -383,6 +389,69 @@ static void lo_lookup(fuse_req_t req, fuse_ino_t parent, const char *name)

     }

 }

+/*

+ * On some archs, setres*id is limited to 2^16 but they

+ * provide setres*id32 variants that allow 2^32.

+ * Others just let setres*id do 2^32 anyway.

+ */

+#ifdef SYS_setresgid32

+#define OURSYS_setresgid SYS_setresgid32

+#else

+#define OURSYS_setresgid SYS_setresgid

+#endif

+

+#ifdef SYS_setresuid32

+#define OURSYS_setresuid SYS_setresuid32

+#else

+#define OURSYS_setresuid SYS_setresuid

+#endif

+

+/*

+ * Change to uid/gid of caller so that file is created with

+ * ownership of caller.

+ * TODO: What about selinux context?

+ */

+static int lo_change_cred(fuse_req_t req, struct lo_cred *old)

+{

+    int res;

+

+    old->euid = geteuid();

+    old->egid = getegid();

+

+    res = syscall(OURSYS_setresgid, -1, fuse_req_ctx(req)->gid, -1);

+    if (res == -1) {

+        return errno;

+    }

+

+    res = syscall(OURSYS_setresuid, -1, fuse_req_ctx(req)->uid, -1);

+    if (res == -1) {

+        int errno_save = errno;

+

+        syscall(OURSYS_setresgid, -1, old->egid, -1);

+        return errno_save;

+    }

+

+    return 0;

+}

+

+/* Regain Privileges */

+static void lo_restore_cred(struct lo_cred *old)

+{

+    int res;

+

+    res = syscall(OURSYS_setresuid, -1, old->euid, -1);

+    if (res == -1) {

+        fuse_log(FUSE_LOG_ERR, "seteuid(%u): %m\n", old->euid);

+        exit(1);

+    }

+

+    res = syscall(OURSYS_setresgid, -1, old->egid, -1);

+    if (res == -1) {

+        fuse_log(FUSE_LOG_ERR, "setegid(%u): %m\n", old->egid);

+        exit(1);

+    }

+}

+

 static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent,

                              const char *name, mode_t mode, dev_t rdev,

                              const char *link)

@@ -391,12 +460,21 @@ static void lo_mknod_symlink(fuse_req_t req, fuse_ino_t parent,

     int saverr;

     struct lo_inode *dir = lo_inode(req, parent);

     struct fuse_entry_param e;

+    struct lo_cred old = {};

     saverr = ENOMEM;

+    saverr = lo_change_cred(req, &old;;

+    if (saverr) {

+        goto out;

+    }

+

     res = mknod_wrapper(dir->fd, name, link, mode, rdev);

     saverr = errno;

+

+    lo_restore_cred(&old;;

+

     if (res == -1) {

         goto out;

     }

@@ -794,26 +872,34 @@ static void lo_create(fuse_req_t req, fuse_ino_t parent, const char *name,

     struct lo_data *lo = lo_data(req);

     struct fuse_entry_param e;

     int err;

+    struct lo_cred old = {};

     if (lo_debug(req)) {

         fuse_log(FUSE_LOG_DEBUG, "lo_create(parent=%" PRIu64 ", name=%s)\n",

                  parent, name);

     }

+    err = lo_change_cred(req, &old;;

+    if (err) {

+        goto out;

+    }

+

     fd = openat(lo_fd(req, parent), name, (fi->flags | O_CREAT) & ~O_NOFOLLOW,

                 mode);

-    if (fd == -1) {

-        return (void)fuse_reply_err(req, errno);

-    }

+    err = fd == -1 ? errno : 0;

+    lo_restore_cred(&old;;

-    fi->fh = fd;

+    if (!err) {

+        fi->fh = fd;

+        err = lo_do_lookup(req, parent, name, &e);

+    }

     if (lo->cache == CACHE_NEVER) {

         fi->direct_io = 1;

     } else if (lo->cache == CACHE_ALWAYS) {

         fi->keep_cache = 1;

     }

-    err = lo_do_lookup(req, parent, name, &e);

+out:

     if (err) {

         fuse_reply_err(req, err);

     } else {