From: Stefan Hajnoczi <stefanha@redhat.com>

Date: Mon, 27 Jan 2020 19:01:26 +0000

Subject: [PATCH] virtiofsd: use /proc/self/fd/ O_PATH file descriptor

MIME-Version: 1.0

Content-Type: text/plain; charset=UTF-8

Content-Transfer-Encoding: 8bit

Sandboxing will remove /proc from the mount namespace so we can no

longer build string paths into "/proc/self/fd/...".

Keep an O_PATH file descriptor so we can still re-open fds via

/proc/self/fd.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>

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

(cherry picked from commit 9f59d175e2ca96f0b87f534dba69ea547dd35945)

---

 tools/virtiofsd/passthrough_ll.c | 130 ++++++++++++++++++++++++-------

 1 file changed, 103 insertions(+), 27 deletions(-)

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

index e3d65c3676..e2e2211ea1 100644

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

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

@@ -110,6 +110,9 @@ struct lo_data {

     struct lo_map ino_map; /* protected by lo->mutex */

     struct lo_map dirp_map; /* protected by lo->mutex */

     struct lo_map fd_map; /* protected by lo->mutex */

+

+    /* An O_PATH file descriptor to /proc/self/fd/ */

+    int proc_self_fd;

 };

 static const struct fuse_opt lo_opts[] = {

@@ -379,9 +382,9 @@ static int lo_parent_and_name(struct lo_data *lo, struct lo_inode *inode,

     int res;

 retry:

-    sprintf(procname, "/proc/self/fd/%i", inode->fd);

+    sprintf(procname, "%i", inode->fd);

-    res = readlink(procname, path, PATH_MAX);

+    res = readlinkat(lo->proc_self_fd, procname, path, PATH_MAX);

     if (res < 0) {

         fuse_log(FUSE_LOG_WARNING, "%s: readlink failed: %m\n", __func__);

         goto fail_noretry;

@@ -477,9 +480,9 @@ static int utimensat_empty(struct lo_data *lo, struct lo_inode *inode,

         }

         return res;

     }

-    sprintf(path, "/proc/self/fd/%i", inode->fd);

+    sprintf(path, "%i", inode->fd);

-    return utimensat(AT_FDCWD, path, tv, 0);

+    return utimensat(lo->proc_self_fd, path, tv, 0);

 fallback:

     res = lo_parent_and_name(lo, inode, path, &parent);

@@ -535,8 +538,8 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,

         if (fi) {

             res = fchmod(fd, attr->st_mode);

         } else {

-            sprintf(procname, "/proc/self/fd/%i", ifd);

-            res = chmod(procname, attr->st_mode);

+            sprintf(procname, "%i", ifd);

+            res = fchmodat(lo->proc_self_fd, procname, attr->st_mode, 0);

         }

         if (res == -1) {

             goto out_err;

@@ -552,11 +555,23 @@ static void lo_setattr(fuse_req_t req, fuse_ino_t ino, struct stat *attr,

         }

     }

     if (valid & FUSE_SET_ATTR_SIZE) {

+        int truncfd;

+

         if (fi) {

-            res = ftruncate(fd, attr->st_size);

+            truncfd = fd;

         } else {

-            sprintf(procname, "/proc/self/fd/%i", ifd);

-            res = truncate(procname, attr->st_size);

+            sprintf(procname, "%i", ifd);

+            truncfd = openat(lo->proc_self_fd, procname, O_RDWR);

+            if (truncfd < 0) {

+                goto out_err;

+            }

+        }

+

+        res = ftruncate(truncfd, attr->st_size);

+        if (!fi) {

+            saverr = errno;

+            close(truncfd);

+            errno = saverr;

         }

         if (res == -1) {

             goto out_err;

@@ -874,9 +889,9 @@ static int linkat_empty_nofollow(struct lo_data *lo, struct lo_inode *inode,

         return res;

     }

-    sprintf(path, "/proc/self/fd/%i", inode->fd);

+    sprintf(path, "%i", inode->fd);

-    return linkat(AT_FDCWD, path, dfd, name, AT_SYMLINK_FOLLOW);

+    return linkat(lo->proc_self_fd, path, dfd, name, AT_SYMLINK_FOLLOW);

 fallback:

     res = lo_parent_and_name(lo, inode, path, &parent);

@@ -1404,8 +1419,8 @@ static void lo_open(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi)

         fi->flags &= ~O_APPEND;

     }

-    sprintf(buf, "/proc/self/fd/%i", lo_fd(req, ino));

-    fd = open(buf, fi->flags & ~O_NOFOLLOW);

+    sprintf(buf, "%i", lo_fd(req, ino));

+    fd = openat(lo->proc_self_fd, buf, fi->flags & ~O_NOFOLLOW);

     if (fd == -1) {

         return (void)fuse_reply_err(req, errno);

     }

@@ -1458,7 +1473,6 @@ static void lo_fsync(fuse_req_t req, fuse_ino_t ino, int datasync,

                      struct fuse_file_info *fi)

 {

     int res;

-    (void)ino;

     int fd;

     char *buf;

@@ -1466,12 +1480,14 @@ static void lo_fsync(fuse_req_t req, fuse_ino_t ino, int datasync,

              (void *)fi);

     if (!fi) {

-        res = asprintf(&buf, "/proc/self/fd/%i", lo_fd(req, ino));

+        struct lo_data *lo = lo_data(req);

+

+        res = asprintf(&buf, "%i", lo_fd(req, ino));

         if (res == -1) {

             return (void)fuse_reply_err(req, errno);

         }

-        fd = open(buf, O_RDWR);

+        fd = openat(lo->proc_self_fd, buf, O_RDWR);

         free(buf);

         if (fd == -1) {

             return (void)fuse_reply_err(req, errno);

@@ -1587,11 +1603,13 @@ static void lo_flock(fuse_req_t req, fuse_ino_t ino, struct fuse_file_info *fi,

 static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

                         size_t size)

 {

+    struct lo_data *lo = lo_data(req);

     char *value = NULL;

     char procname[64];

     struct lo_inode *inode;

     ssize_t ret;

     int saverr;

+    int fd = -1;

     inode = lo_inode(req, ino);

     if (!inode) {

@@ -1616,7 +1634,11 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

         goto out;

     }

-    sprintf(procname, "/proc/self/fd/%i", inode->fd);

+    sprintf(procname, "%i", inode->fd);

+    fd = openat(lo->proc_self_fd, procname, O_RDONLY);

+    if (fd < 0) {

+        goto out_err;

+    }

     if (size) {

         value = malloc(size);

@@ -1624,7 +1646,7 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

             goto out_err;

         }

-        ret = getxattr(procname, name, value, size);

+        ret = fgetxattr(fd, name, value, size);

         if (ret == -1) {

             goto out_err;

         }

@@ -1635,7 +1657,7 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

         fuse_reply_buf(req, value, ret);

     } else {

-        ret = getxattr(procname, name, NULL, 0);

+        ret = fgetxattr(fd, name, NULL, 0);

         if (ret == -1) {

             goto out_err;

         }

@@ -1644,6 +1666,10 @@ static void lo_getxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

     }

 out_free:

     free(value);

+

+    if (fd >= 0) {

+        close(fd);

+    }

     return;

 out_err:

@@ -1655,11 +1681,13 @@ out:

 static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)

 {

+    struct lo_data *lo = lo_data(req);

     char *value = NULL;

     char procname[64];

     struct lo_inode *inode;

     ssize_t ret;

     int saverr;

+    int fd = -1;

     inode = lo_inode(req, ino);

     if (!inode) {

@@ -1683,7 +1711,11 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)

         goto out;

     }

-    sprintf(procname, "/proc/self/fd/%i", inode->fd);

+    sprintf(procname, "%i", inode->fd);

+    fd = openat(lo->proc_self_fd, procname, O_RDONLY);

+    if (fd < 0) {

+        goto out_err;

+    }

     if (size) {

         value = malloc(size);

@@ -1691,7 +1723,7 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)

             goto out_err;

         }

-        ret = listxattr(procname, value, size);

+        ret = flistxattr(fd, value, size);

         if (ret == -1) {

             goto out_err;

         }

@@ -1702,7 +1734,7 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)

         fuse_reply_buf(req, value, ret);

     } else {

-        ret = listxattr(procname, NULL, 0);

+        ret = flistxattr(fd, NULL, 0);

         if (ret == -1) {

             goto out_err;

         }

@@ -1711,6 +1743,10 @@ static void lo_listxattr(fuse_req_t req, fuse_ino_t ino, size_t size)

     }

 out_free:

     free(value);

+

+    if (fd >= 0) {

+        close(fd);

+    }

     return;

 out_err:

@@ -1724,9 +1760,11 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

                         const char *value, size_t size, int flags)

 {

     char procname[64];

+    struct lo_data *lo = lo_data(req);

     struct lo_inode *inode;

     ssize_t ret;

     int saverr;

+    int fd = -1;

     inode = lo_inode(req, ino);

     if (!inode) {

@@ -1751,21 +1789,31 @@ static void lo_setxattr(fuse_req_t req, fuse_ino_t ino, const char *name,

         goto out;

     }

-    sprintf(procname, "/proc/self/fd/%i", inode->fd);

+    sprintf(procname, "%i", inode->fd);

+    fd = openat(lo->proc_self_fd, procname, O_RDWR);

+    if (fd < 0) {

+        saverr = errno;

+        goto out;

+    }

-    ret = setxattr(procname, name, value, size, flags);

+    ret = fsetxattr(fd, name, value, size, flags);

     saverr = ret == -1 ? errno : 0;

 out:

+    if (fd >= 0) {

+        close(fd);

+    }

     fuse_reply_err(req, saverr);

 }

 static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *name)

 {

     char procname[64];

+    struct lo_data *lo = lo_data(req);

     struct lo_inode *inode;

     ssize_t ret;

     int saverr;

+    int fd = -1;

     inode = lo_inode(req, ino);

     if (!inode) {

@@ -1789,12 +1837,20 @@ static void lo_removexattr(fuse_req_t req, fuse_ino_t ino, const char *name)

         goto out;

     }

-    sprintf(procname, "/proc/self/fd/%i", inode->fd);

+    sprintf(procname, "%i", inode->fd);

+    fd = openat(lo->proc_self_fd, procname, O_RDWR);

+    if (fd < 0) {

+        saverr = errno;

+        goto out;

+    }

-    ret = removexattr(procname, name);

+    ret = fremovexattr(fd, name);

     saverr = ret == -1 ? errno : 0;

 out:

+    if (fd >= 0) {

+        close(fd);

+    }

     fuse_reply_err(req, saverr);

 }

@@ -1887,12 +1943,25 @@ static void print_capabilities(void)

     printf("}\n");

 }

+static void setup_proc_self_fd(struct lo_data *lo)

+{

+    lo->proc_self_fd = open("/proc/self/fd", O_PATH);

+    if (lo->proc_self_fd == -1) {

+        fuse_log(FUSE_LOG_ERR, "open(/proc/self/fd, O_PATH): %m\n");

+        exit(1);

+    }

+}

+

 int main(int argc, char *argv[])

 {

     struct fuse_args args = FUSE_ARGS_INIT(argc, argv);

     struct fuse_session *se;

     struct fuse_cmdline_opts opts;

-    struct lo_data lo = { .debug = 0, .writeback = 0 };

+    struct lo_data lo = {

+        .debug = 0,

+        .writeback = 0,

+        .proc_self_fd = -1,

+    };

     struct lo_map_elem *root_elem;

     int ret = -1;

@@ -2003,6 +2072,9 @@ int main(int argc, char *argv[])

     fuse_daemonize(opts.foreground);

+    /* Must be after daemonize to get the right /proc/self/fd */

+    setup_proc_self_fd(&lo);

+

     /* Block until ctrl+c or fusermount -u */

     ret = virtio_loop(se);

@@ -2018,6 +2090,10 @@ err_out1:

     lo_map_destroy(&lo.dirp_map);

     lo_map_destroy(&lo.ino_map);

+    if (lo.proc_self_fd >= 0) {

+        close(lo.proc_self_fd);

+    }

+

     if (lo.root.fd >= 0) {

         close(lo.root.fd);

     }