[PATCH 4.19 19/48] net/9p: validate fds in p9_fd_open

Greg Kroah-Hartman
2020-08-10T15:29:54Z

From: Christoph Hellwig <hch@lst.de>

[ Upstream commit a39c46067c845a8a2d7144836e9468b7f072343e ]

p9_fd_open just fgets file descriptors passed in from userspace, but
doesn't verify that they are valid for read or writing. This gets
cought down in the VFS when actually attempting a read or write, but
a new warning added in linux-next upsets syzcaller.

Fix this by just verifying the fds early on.

Link: http://lkml.kernel.org/r/20200710085722.435850-1-hch@lst.de
Reported-by: syzbot+e6f77e16ff68b2434a2c@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
[Dominique: amend goto as per Doug Nazar's review]
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/trans_fd.c | 24 ++++++++++++++++--------
1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index d28c2cc9618fa..b6dcb40fa8a7d 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -831,20 +831,28 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd)
return -ENOMEM;

ts->rd = fget(rfd);
+ if (!ts->rd)
+ goto out_free_ts;
+ if (!(ts->rd->f_mode & FMODE_READ))
+ goto out_put_rd;
ts->wr = fget(wfd);
- if (!ts->rd || !ts->wr) {
- if (ts->rd)
- fput(ts->rd);
- if (ts->wr)
- fput(ts->wr);
- kfree(ts);
- return -EIO;
- }
+ if (!ts->wr)
+ goto out_put_rd;
+ if (!(ts->wr->f_mode & FMODE_WRITE))
+ goto out_put_wr;

client->trans = ts;
client->status = Connected;

return 0;
+
+out_put_wr:
+ fput(ts->wr);
+out_put_rd:
+ fput(ts->rd);
+out_free_ts:
+ kfree(ts);
+ return -EIO;
}

static int p9_socket_open(struct p9_client *client, struct socket *csocket)
--
2.25.1