[Qemu-devel] [PATCH] hw/9pfs: fix P9_STATS_GEN handling

["Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>]

Currently we have few issues with P9_STATS_GEN:

 - We don't try to read st_gen anything except files or directories, but
   still set P9_STATS_GEN bit in st_result_mask. It may mislead client:
   we present garbage as valid st_gen.

 - If we failed to get valid st_gen with ENOTTY, we ignore error, but
   still set P9_STATS_GEN bit in st_result_mask.

 - If we failed to get valid st_gen with any other errno, we fail
   getattr altogether. It's excessive: we block valid client use-cases,
   like chdir(2) to non-readable directory with execution bit set.

The patch fixes these issues and cleanup code a bit.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 hw/9pfs/cofile.c           |  4 ----
 hw/9pfs/virtio-9p-handle.c |  8 +++++++-
 hw/9pfs/virtio-9p-local.c  | 10 ++++++----
 hw/9pfs/virtio-9p-proxy.c  |  3 ++-
 hw/9pfs/virtio-9p.c        | 12 ++++++++++--
 5 files changed, 25 insertions(+), 12 deletions(-)

diff --git a/hw/9pfs/cofile.c b/hw/9pfs/cofile.c
index 194c1306c6..2efebf3571 100644
--- a/hw/9pfs/cofile.c
+++ b/hw/9pfs/cofile.c
@@ -38,10 +38,6 @@ int v9fs_co_st_gen(V9fsPDU *pdu, V9fsPath *path, mode_t st_mode,
             });
         v9fs_path_unlock(s);
     }
-    /* The ioctl may not be supported depending on the path */
-    if (err == -ENOTTY) {
-        err = 0;
-    }
     return err;
 }
 
diff --git a/hw/9pfs/virtio-9p-handle.c b/hw/9pfs/virtio-9p-handle.c
index fe8e0ed19d..17002a3d28 100644
--- a/hw/9pfs/virtio-9p-handle.c
+++ b/hw/9pfs/virtio-9p-handle.c
@@ -582,6 +582,7 @@ static int handle_unlinkat(FsContext *ctx, V9fsPath *dir,
 static int handle_ioc_getversion(FsContext *ctx, V9fsPath *path,
                                  mode_t st_mode, uint64_t *st_gen)
 {
+#ifdef FS_IOC_GETVERSION
     int err;
     V9fsFidOpenState fid_open;
 
@@ -590,7 +591,8 @@ static int handle_ioc_getversion(FsContext *ctx, V9fsPath *path,
      * We can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-            return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = handle_open(ctx, path, O_RDONLY, &fid_open);
     if (err < 0) {
@@ -599,6 +601,10 @@ static int handle_ioc_getversion(FsContext *ctx, V9fsPath *path,
     err = ioctl(fid_open.fd, FS_IOC_GETVERSION, st_gen);
     handle_close(ctx, &fid_open);
     return err;
+#else
+    errno = ENOTTY;
+    return -1;
+#endif
 }
 
 static int handle_init(FsContext *ctx)
diff --git a/hw/9pfs/virtio-9p-local.c b/hw/9pfs/virtio-9p-local.c
index fc93e9e6e8..df0dbffa7a 100644
--- a/hw/9pfs/virtio-9p-local.c
+++ b/hw/9pfs/virtio-9p-local.c
@@ -1068,8 +1068,8 @@ err_out:
 static int local_ioc_getversion(FsContext *ctx, V9fsPath *path,
                                 mode_t st_mode, uint64_t *st_gen)
 {
-    int err;
 #ifdef FS_IOC_GETVERSION
+    int err;
     V9fsFidOpenState fid_open;
 
     /*
@@ -1077,7 +1077,8 @@ static int local_ioc_getversion(FsContext *ctx, V9fsPath *path,
      * We can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-            return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = local_open(ctx, path, O_RDONLY, &fid_open);
     if (err < 0) {
@@ -1085,10 +1086,11 @@ static int local_ioc_getversion(FsContext *ctx, V9fsPath *path,
     }
     err = ioctl(fid_open.fd, FS_IOC_GETVERSION, st_gen);
     local_close(ctx, &fid_open);
+    return err;
 #else
-    err = -ENOTTY;
+    errno = ENOTTY;
+    return -1;
 #endif
-    return err;
 }
 
 static int local_init(FsContext *ctx)
diff --git a/hw/9pfs/virtio-9p-proxy.c b/hw/9pfs/virtio-9p-proxy.c
index 5f44bb758b..b57966d9d8 100644
--- a/hw/9pfs/virtio-9p-proxy.c
+++ b/hw/9pfs/virtio-9p-proxy.c
@@ -1086,7 +1086,8 @@ static int proxy_ioc_getversion(FsContext *fs_ctx, V9fsPath *path,
      * we can get fd for regular files and directories only
      */
     if (!S_ISREG(st_mode) && !S_ISDIR(st_mode)) {
-        return 0;
+        errno = ENOTTY;
+        return -1;
     }
     err = v9fs_request(fs_ctx->private, T_GETVERSION, st_gen, "s", path);
     if (err < 0) {
diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 8cbb8ae32a..3e51fcd152 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -1080,10 +1080,18 @@ static void v9fs_getattr(void *opaque)
     /*  fill st_gen if requested and supported by underlying fs */
     if (request_mask & P9_STATS_GEN) {
         retval = v9fs_co_st_gen(pdu, &fidp->path, stbuf.st_mode, &v9stat_dotl);
-        if (retval < 0) {
+        switch (retval) {
+        case 0:
+            /* we have valid st_gen: update result mask */
+            v9stat_dotl.st_result_mask |= P9_STATS_GEN;
+            break;
+        case -EINTR:
+            /* request cancelled */
             goto out;
+        default:
+            /* failed to get st_gen: not fatal, ignore */
+            break;
         }
-        v9stat_dotl.st_result_mask |= P9_STATS_GEN;
     }
     retval = pdu_marshal(pdu, offset, "A", &v9stat_dotl);
     if (retval < 0) {
-- 
1.8.4.rc3