9p: take write lock on fid path updates

Recent commit 5b76ef50f62079a fixed a race where v9fs_co_open2() could
possibly overwrite a fid path with v9fs_path_copy() while it is being
accessed by some other thread, ie, use-after-free that can be detected
by ASAN with a custom 9p client.

It turns out that the same can happen at several locations where
v9fs_path_copy() is used to set the fid path. The fix is again to
take the write lock.

Cc: P J P <ppandit@redhat.com>
Reported-by: zhibin hu <noirfate@gmail.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
---
 hw/9pfs/9p.c |   15 +++++++++++++++
 1 file changed, 15 insertions(+)

+-- On Thu, 15 Nov 2018, Greg Kurz wrote --+
| Recent commit 5b76ef50f62079a fixed a race where v9fs_co_open2() could
| possibly overwrite a fid path with v9fs_path_copy() while it is being
| accessed by some other thread, ie, use-after-free that can be detected
| by ASAN with a custom 9p client.
| 
| It turns out that the same can happen at several locations where
| v9fs_path_copy() is used to set the fid path. The fix is again to
| take the write lock.
| 
| Cc: P J P <ppandit@redhat.com>
| Reported-by: zhibin hu <noirfate@gmail.com>
| Signed-off-by: Greg Kurz <groug@kaod.org>
| ---
|  hw/9pfs/9p.c |   15 +++++++++++++++
|  1 file changed, 15 insertions(+)
| 
| diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
| index eef289e394d4..267a25533b77 100644
| --- a/hw/9pfs/9p.c
| +++ b/hw/9pfs/9p.c
| @@ -1391,7 +1391,9 @@ static void coroutine_fn v9fs_walk(void *opaque)
|              err = -EINVAL;
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|      } else {
|          newfidp = alloc_fid(s, newfid);
|          if (newfidp == NULL) {
| @@ -2160,6 +2162,7 @@ static void coroutine_fn v9fs_create(void *opaque)
|      V9fsString extension;
|      int iounit;
|      V9fsPDU *pdu = opaque;
| +    V9fsState *s = pdu->s;
|  
|      v9fs_path_init(&path);
|      v9fs_string_init(&name);
| @@ -2200,7 +2203,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|          if (err < 0) {
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|          err = v9fs_co_opendir(pdu, fidp);
|          if (err < 0) {
|              goto out;
| @@ -2216,7 +2221,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|          if (err < 0) {
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|      } else if (perm & P9_STAT_MODE_LINK) {
|          int32_t ofid = atoi(extension.data);
|          V9fsFidState *ofidp = get_fid(pdu, ofid);
| @@ -2234,7 +2241,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|              fidp->fid_type = P9_FID_NONE;
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|          err = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
|          if (err < 0) {
|              fidp->fid_type = P9_FID_NONE;
| @@ -2272,7 +2281,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|          if (err < 0) {
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|      } else if (perm & P9_STAT_MODE_NAMED_PIPE) {
|          err = v9fs_co_mknod(pdu, fidp, &name, fidp->uid, -1,
|                              0, S_IFIFO | (perm & 0777), &stbuf);
| @@ -2283,7 +2294,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|          if (err < 0) {
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|      } else if (perm & P9_STAT_MODE_SOCKET) {
|          err = v9fs_co_mknod(pdu, fidp, &name, fidp->uid, -1,
|                              0, S_IFSOCK | (perm & 0777), &stbuf);
| @@ -2294,7 +2307,9 @@ static void coroutine_fn v9fs_create(void *opaque)
|          if (err < 0) {
|              goto out;
|          }
| +        v9fs_path_write_lock(s);
|          v9fs_path_copy(&fidp->path, &path);
| +        v9fs_path_unlock(s);
|      } else {
|          err = v9fs_co_open2(pdu, fidp, &name, -1,
|                              omode_to_uflags(mode)|O_CREAT, perm, &stbuf);
| 

Looks okay.
Reviewed-by: Prasad J Pandit <pjp@fedoraproject.org>

Thank you.
--
Prasad J Pandit / Red Hat Product Security Team
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