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9p: write lock path in v9fs_co_open2()

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The assumption that the fid cannot be used by any other operation is
wrong. At least, nothing prevents a misbehaving client to create a
file with a given fid, and to pass this fid to some other operation
at the same time (ie, without waiting for the response to the creation
request). The call to v9fs_path_copy() performed by the worker thread
after the file was created can race with any access to the fid path
performed by some other thread. This causes use-after-free issues that
can be detected by ASAN with a custom 9p client.

Unlike other operations that only read the fid path, v9fs_co_open2()
does modify it. It should hence 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>
This commit is contained in:
Greg Kurz 2018-11-07 01:00:04 +01:00
parent a7ce790a02
commit 5b76ef50f6
1 changed files with 3 additions and 3 deletions
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6
hw/9pfs/cofile.c
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@ -140,10 +140,10 @@ int coroutine_fn v9fs_co_open2(V9fsPDU *pdu, V9fsFidState *fidp,
cred.fc_gid = gid; cred.fc_gid = gid;
/* /*
* Hold the directory fid lock so that directory path name * Hold the directory fid lock so that directory path name
* don't change. Read lock is fine because this fid cannot * don't change. Take the write lock to be sure this fid
* be used by any other operation. * cannot be used by another operation.
*/ */
v9fs_path_read_lock(s); v9fs_path_write_lock(s);
v9fs_co_run_in_worker( v9fs_co_run_in_worker(
{ {
err = s->ops->open2(&s->ctx, &fidp->path, err = s->ops->open2(&s->ctx, &fidp->path,