9pfs: forbid . and .. in file names

According to the 9P spec http://man.cat-v.org/plan_9/5/open about the
create request:

The names . and .. are special; it is illegal to create files with these
names.

This patch causes the create and lcreate requests to fail with EINVAL if
the file name is either "." or "..".

Even if it isn't explicitly written in the spec, this patch extends the
checking to all requests that may cause a directory entry to be created:

    - mknod
    - rename
    - renameat
    - mkdir
    - link
    - symlink

The unlinkat request also gets patched for consistency (even if
rmdir("foo/..") is expected to fail according to POSIX.1-2001).

The various error values come from the linux manual pages.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 51 insertions, 0 deletions

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 385269ea0a..51c6f9883b 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1497,6 +1497,11 @@ static void v9fs_lcreate(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, dfid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -2096,6 +2101,11 @@ static void v9fs_create(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -EINVAL;
@@ -2266,6 +2276,11 @@ static void v9fs_symlink(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -EINVAL;
@@ -2345,6 +2360,11 @@ static void v9fs_link(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -ENOENT;
@@ -2433,6 +2453,16 @@ static void v9fs_unlinkat(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data)) {
+        err = -EINVAL;
+        goto out_nofid;
+    }
+
+    if (!strcmp("..", name.data)) {
+        err = -ENOTEMPTY;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -EINVAL;
@@ -2545,6 +2575,11 @@ static void v9fs_rename(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EISDIR;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -2662,6 +2697,12 @@ static void v9fs_renameat(void *opaque)
         goto out_err;
     }
 
+    if (!strcmp(".", old_name.data) || !strcmp("..", old_name.data) ||
+        !strcmp(".", new_name.data) || !strcmp("..", new_name.data)) {
+        err = -EISDIR;
+        goto out_err;
+    }
+
     v9fs_path_write_lock(s);
     err = v9fs_complete_renameat(pdu, olddirfid,
                                  &old_name, newdirfid, &new_name);
@@ -2877,6 +2918,11 @@ static void v9fs_mknod(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -3033,6 +3079,11 @@ static void v9fs_mkdir(void *opaque)
         goto out_nofid;
     }
 
+    if (!strcmp(".", name.data) || !strcmp("..", name.data)) {
+        err = -EEXIST;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;