Re: [Qemu-devel] 9p mapped-* security model infos are architecture-specific

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> writes:

> Michael Tokarev <mjt@tls.msk.ru> writes:
>
>> Apparently the the mapped-* security models results in a raw bytes
>> being dumped to host without any architecture normalization (in
>> host byte order).  This may even lead to security issues in guest
>> when the same files are served from another host for example.
>>
>> This bug has been initially submitted against debian qemu package, see
>> http://bugs.debian.org/755740
>>
>
> Thanks for reporting the bug. Yes we do have issue with
> mapped-xattr. But mapped-file should be ok. We record the uid/gid as
> string in the file.

What would be the best way to fix this in a backward compatible way ?
Considering most of the users will be little endian host, we could do "always
store in little endian format" which of-course will break big-endian
hosts. We could possibly ask them to update xattr using external tools ?

diff --git a/hw/9pfs/virtio-9p-local.c b/hw/9pfs/virtio-9p-local.c
index 3b0b6a9b1d7d..cd662410420e 100644
--- a/hw/9pfs/virtio-9p-local.c
+++ b/hw/9pfs/virtio-9p-local.c
@@ -135,17 +135,17 @@ static int local_lstat(FsContext *fs_ctx, V9fsPath *fs_path, struct stat *stbuf)
         mode_t tmp_mode;
         dev_t tmp_dev;
         if (getxattr(buffer, "user.virtfs.uid", &tmp_uid, sizeof(uid_t)) > 0) {
-            stbuf->st_uid = tmp_uid;
+            stbuf->st_uid = le32_to_cpu(tmp_uid);
         }
         if (getxattr(buffer, "user.virtfs.gid", &tmp_gid, sizeof(gid_t)) > 0) {
-            stbuf->st_gid = tmp_gid;
+            stbuf->st_gid = le32_to_cpu(tmp_gid);
         }
         if (getxattr(buffer, "user.virtfs.mode",
                     &tmp_mode, sizeof(mode_t)) > 0) {
-            stbuf->st_mode = tmp_mode;
+            stbuf->st_mode = le32_to_cpu(tmp_mode);
         }
         if (getxattr(buffer, "user.virtfs.rdev", &tmp_dev, sizeof(dev_t)) > 0) {
-                stbuf->st_rdev = tmp_dev;
+            stbuf->st_rdev = le64_to_cpu(tmp_dev);
         }
     } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
         local_mapped_file_attr(fs_ctx, path, stbuf);
@@ -255,29 +255,29 @@ static int local_set_xattr(const char *path, FsCred *credp)
     int err;
 
     if (credp->fc_uid != -1) {
-        err = setxattr(path, "user.virtfs.uid", &credp->fc_uid, sizeof(uid_t),
-                0);
+        uint32_t tmp_uid = cpu_to_le32(credp->fc_uid);
+        err = setxattr(path, "user.virtfs.uid", &tmp_uid, sizeof(uid_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_gid != -1) {
-        err = setxattr(path, "user.virtfs.gid", &credp->fc_gid, sizeof(gid_t),
-                0);
+        uint32_t tmp_gid = cpu_to_le32(credp->fc_gid);
+        err = setxattr(path, "user.virtfs.gid", &tmp_gid, sizeof(gid_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_mode != -1) {
-        err = setxattr(path, "user.virtfs.mode", &credp->fc_mode,
-                sizeof(mode_t), 0);
+        uint32_t tmp_mode = cpu_to_le32(credp->fc_mode);
+        err = setxattr(path, "user.virtfs.mode", &tmp_mode, sizeof(mode_t), 0);
         if (err) {
             return err;
         }
     }
     if (credp->fc_rdev != -1) {
-        err = setxattr(path, "user.virtfs.rdev", &credp->fc_rdev,
-                sizeof(dev_t), 0);
+        uint64_t tmp_rdev = cpu_to_le32(credp->fc_rdev);
+        err = setxattr(path, "user.virtfs.rdev", &tmp_rdev, sizeof(dev_t), 0);
         if (err) {
             return err;
         }
@@ -630,21 +630,17 @@ static int local_fstat(FsContext *fs_ctx, int fid_type,
         mode_t tmp_mode;
         dev_t tmp_dev;
 
-        if (fgetxattr(fd, "user.virtfs.uid",
-                      &tmp_uid, sizeof(uid_t)) > 0) {
-            stbuf->st_uid = tmp_uid;
+        if (fgetxattr(fd, "user.virtfs.uid", &tmp_uid, sizeof(uid_t)) > 0) {
+            stbuf->st_uid = le32_to_cpu(tmp_uid);
         }
-        if (fgetxattr(fd, "user.virtfs.gid",
-                      &tmp_gid, sizeof(gid_t)) > 0) {
-            stbuf->st_gid = tmp_gid;
+        if (fgetxattr(fd, "user.virtfs.gid", &tmp_gid, sizeof(gid_t)) > 0) {
+            stbuf->st_gid = le32_to_cpu(tmp_gid);
         }
-        if (fgetxattr(fd, "user.virtfs.mode",
-                      &tmp_mode, sizeof(mode_t)) > 0) {
-            stbuf->st_mode = tmp_mode;
+        if (fgetxattr(fd, "user.virtfs.mode", &tmp_mode, sizeof(mode_t)) > 0) {
+            stbuf->st_mode = le32_to_cpu(tmp_mode);
         }
-        if (fgetxattr(fd, "user.virtfs.rdev",
-                      &tmp_dev, sizeof(dev_t)) > 0) {
-                stbuf->st_rdev = tmp_dev;
+        if (fgetxattr(fd, "user.virtfs.rdev", &tmp_dev, sizeof(dev_t)) > 0) {
+            stbuf->st_rdev = le64_to_cpu(tmp_dev);
         }
     } else if (fs_ctx->export_flags & V9FS_SM_MAPPED_FILE) {
         errno = EOPNOTSUPP;