[Qemu-devel] [PATCH v4 1/3] 9pfs: forbid illegal path names

[Greg Kurz]

Empty path components don't make sense for most commands and may cause
undefined behavior, depending on the backend.

Also, the walk request described in the 9P spec [1] clearly shows that
the client is supposed to send individual path components: the official
linux client never sends portions of path containing the / character for
example.

Moreover, the 9P spec [2] also states that a system can decide to restrict
the set of supported characters used in path components, with an explicit
mention "to remove slashes from name components".

This patch introduces a new name_is_illegal() helper that checks the
names sent by the client are not empty and don't contain unwanted chars.
Since 9pfs is only supported on linux hosts, only the / character is
checked at the moment. When support for other hosts (AKA. win32) is added,
other chars may need to be blacklisted as well.

If a client sends an illegal path component, the request will fail and
ENOENT is returned to the client.

[1] http://man.cat-v.org/plan_9/5/walk
[2] http://man.cat-v.org/plan_9/5/intro

Suggested-by: Peter Maydell <address@hidden>
Signed-off-by: Greg Kurz <address@hidden>
---
v4: dropped the checking of the symbolic link target name: because a target
    can be a full path and thus contain '/' and linux already complains if
    it is an empty string. When the symlink gets dereferenced, slashes are
    interpreted as the usual path component separator.
---
 hw/9pfs/9p.c |   56 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 56 insertions(+)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index b6b02b46a9da..385269ea0ac3 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1256,6 +1256,11 @@ static int v9fs_walk_marshal(V9fsPDU *pdu, uint16_t 
nwnames, V9fsQID *qids)
     return offset;
 }
 
+static bool name_is_illegal(const char *name)
+{
+    return !*name || strchr(name, '/') != NULL;
+}
+
 static void v9fs_walk(void *opaque)
 {
     int name_idx;
@@ -1289,6 +1294,10 @@ static void v9fs_walk(void *opaque)
             if (err < 0) {
                 goto out_nofid;
             }
+            if (name_is_illegal(wnames[i].data)) {
+                err = -ENOENT;
+                goto out_nofid;
+            }
             offset += err;
         }
     } else if (nwnames > P9_MAXWELEM) {
@@ -1483,6 +1492,11 @@ static void v9fs_lcreate(void *opaque)
     }
     trace_v9fs_lcreate(pdu->tag, pdu->id, dfid, flags, mode, gid);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, dfid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -2077,6 +2091,11 @@ static void v9fs_create(void *opaque)
     }
     trace_v9fs_create(pdu->tag, pdu->id, fid, name.data, perm, mode);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -EINVAL;
@@ -2242,6 +2261,11 @@ static void v9fs_symlink(void *opaque)
     }
     trace_v9fs_symlink(pdu->tag, pdu->id, dfid, name.data, symname.data, gid);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -EINVAL;
@@ -2316,6 +2340,11 @@ static void v9fs_link(void *opaque)
     }
     trace_v9fs_link(pdu->tag, pdu->id, dfid, oldfid, name.data);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -ENOENT;
@@ -2398,6 +2427,12 @@ static void v9fs_unlinkat(void *opaque)
     if (err < 0) {
         goto out_nofid;
     }
+
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     dfidp = get_fid(pdu, dfid);
     if (dfidp == NULL) {
         err = -EINVAL;
@@ -2504,6 +2539,12 @@ static void v9fs_rename(void *opaque)
     if (err < 0) {
         goto out_nofid;
     }
+
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -2616,6 +2657,11 @@ static void v9fs_renameat(void *opaque)
         goto out_err;
     }
 
+    if (name_is_illegal(old_name.data) || name_is_illegal(new_name.data)) {
+        err = -ENOENT;
+        goto out_err;
+    }
+
     v9fs_path_write_lock(s);
     err = v9fs_complete_renameat(pdu, olddirfid,
                                  &old_name, newdirfid, &new_name);
@@ -2826,6 +2872,11 @@ static void v9fs_mknod(void *opaque)
     }
     trace_v9fs_mknod(pdu->tag, pdu->id, fid, mode, major, minor);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;
@@ -2977,6 +3028,11 @@ static void v9fs_mkdir(void *opaque)
     }
     trace_v9fs_mkdir(pdu->tag, pdu->id, fid, name.data, mode, gid);
 
+    if (name_is_illegal(name.data)) {
+        err = -ENOENT;
+        goto out_nofid;
+    }
+
     fidp = get_fid(pdu, fid);
     if (fidp == NULL) {
         err = -ENOENT;