[PATCH 4/4] 9p locks: fix glock.client_id leak in do_lock

[Dominique Martinet]

From: Dominique Martinet <dominique.marti...@cea.fr>

the 9p client code overwrites our glock.client_id pointing to a static
buffer by an allocated string holding the network provided value which
we do not care about; free and reset the value as appropriate.

This is almost identical to the leak in v9fs_file_getlock() fixed by
Al Viro in commit ce85dd58ad5a6 ("9p: we are leaking glock.client_id
in v9fs_file_getlock()"), which was returned as an error by a coverity
false positive -- while we are here attempt to make the code slightly
more robust to future change of the net/9p/client code and hopefully
more clear to coverity that there is no problem.

Signed-off-by: Dominique Martinet <dominique.marti...@cea.fr>
---
 fs/9p/vfs_file.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 73857ebaedfb..a25efa782fcc 100644
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -208,6 +208,14 @@ static int v9fs_file_do_lock(struct file *filp, int cmd, 
struct file_lock *fl)
                if (schedule_timeout_interruptible(v9ses->session_lock_timeout)
                                != 0)
                        break;
+               /*
+                * p9_client_lock_dotl overwrites flock.client_id with the
+                * server message, free and reuse the client name
+                */
+               if (flock.client_id != fid->clnt->name) {
+                       kfree(flock.client_id);
+                       flock.client_id = fid->clnt->name;
+               }
        }
 
        /* map 9p status to VFS status */
@@ -239,6 +247,8 @@ static int v9fs_file_do_lock(struct file *filp, int cmd, 
struct file_lock *fl)
                locks_lock_file_wait(filp, fl);
                fl->fl_type = fl_type;
        }
+       if (flock.client_id != fid->clnt->name)
+               kfree(flock.client_id);
 out:
        return res;
 }
@@ -273,7 +283,7 @@ static int v9fs_file_getlock(struct file *filp, struct 
file_lock *fl)
 
        res = p9_client_getlock_dotl(fid, &glock);
        if (res < 0)
-               return res;
+               goto out;
        /* map 9p lock type to os lock type */
        switch (glock.type) {
        case P9_LOCK_TYPE_RDLCK:
@@ -294,7 +304,9 @@ static int v9fs_file_getlock(struct file *filp, struct 
file_lock *fl)
                        fl->fl_end = glock.start + glock.length - 1;
                fl->fl_pid = -glock.proc_id;
        }
-       kfree(glock.client_id);
+out:
+       if (glock.client_id != fid->clnt->name)
+               kfree(glock.client_id);
        return res;
 }
 
-- 
2.17.1