[PATCH 4.14 021/124] 9p locks: fix glock.client_id leak in do_lock

Greg Kroah-Hartman
2018-11-19T16:47:45Z

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

[ Upstream commit b4dc44b3cac9e8327e0655f530ed0c46f2e6214c ]

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.

Link: http://lkml.kernel.org/r/1536339057-21974-5-git-send-email-asmadeus@codewreck.org
Signed-off-by: Dominique Martinet <dominique.martinet@cea.fr>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/9p/vfs_file.c | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)

--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -204,6 +204,14 @@ static int v9fs_file_do_lock(struct file
break;
if (schedule_timeout_interruptible(P9_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 */
@@ -235,6 +243,8 @@ out_unlock:
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;
}
@@ -269,7 +279,7 @@ static int v9fs_file_getlock(struct file

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:
@@ -290,7 +300,9 @@ static int v9fs_file_getlock(struct file
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;
}