From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Marco Elver <elver@google.com>,
syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com,
Dominique Martinet <asmadeus@codewreck.org>,
Sasha Levin <sashal@kernel.org>,
ericvh@kernel.org, lucho@ionkov.net, davem@davemloft.net,
edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
v9fs@lists.linux.dev, netdev@vger.kernel.org
Subject: [PATCH AUTOSEL 6.6 17/18] 9p/trans_fd: Annotate data-racy writes to file::f_flags
Date: Tue, 7 Nov 2023 18:22:11 -0500 [thread overview]
Message-ID: <20231107232231.3775605-17-sashal@kernel.org> (raw)
In-Reply-To: <20231107232231.3775605-1-sashal@kernel.org>
From: Marco Elver <elver@google.com>
[ Upstream commit 355f074609dbf3042900ea9d30fcd2b0c323a365 ]
syzbot reported:
| BUG: KCSAN: data-race in p9_fd_create / p9_fd_create
|
| read-write to 0xffff888130fb3d48 of 4 bytes by task 15599 on cpu 0:
| p9_fd_open net/9p/trans_fd.c:842 [inline]
| p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092
| p9_client_create+0x595/0xa70 net/9p/client.c:1010
| v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410
| v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123
| legacy_get_tree+0x74/0xd0 fs/fs_context.c:611
| vfs_get_tree+0x51/0x190 fs/super.c:1519
| do_new_mount+0x203/0x660 fs/namespace.c:3335
| path_mount+0x496/0xb30 fs/namespace.c:3662
| do_mount fs/namespace.c:3675 [inline]
| __do_sys_mount fs/namespace.c:3884 [inline]
| [...]
|
| read-write to 0xffff888130fb3d48 of 4 bytes by task 15563 on cpu 1:
| p9_fd_open net/9p/trans_fd.c:842 [inline]
| p9_fd_create+0x210/0x250 net/9p/trans_fd.c:1092
| p9_client_create+0x595/0xa70 net/9p/client.c:1010
| v9fs_session_init+0xf9/0xd90 fs/9p/v9fs.c:410
| v9fs_mount+0x69/0x630 fs/9p/vfs_super.c:123
| legacy_get_tree+0x74/0xd0 fs/fs_context.c:611
| vfs_get_tree+0x51/0x190 fs/super.c:1519
| do_new_mount+0x203/0x660 fs/namespace.c:3335
| path_mount+0x496/0xb30 fs/namespace.c:3662
| do_mount fs/namespace.c:3675 [inline]
| __do_sys_mount fs/namespace.c:3884 [inline]
| [...]
|
| value changed: 0x00008002 -> 0x00008802
Within p9_fd_open(), O_NONBLOCK is added to f_flags of the read and
write files. This may happen concurrently if e.g. mounting process
modifies the fd in another thread.
Mark the plain read-modify-writes as intentional data-races, with the
assumption that the result of executing the accesses concurrently will
always result in the same result despite the accesses themselves not
being atomic.
Reported-by: syzbot+e441aeeb422763cc5511@syzkaller.appspotmail.com
Signed-off-by: Marco Elver <elver@google.com>
Link: https://lore.kernel.org/r/ZO38mqkS0TYUlpFp@elver.google.com
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Message-ID: <20231025103445.1248103-1-asmadeus@codewreck.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/9p/trans_fd.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)
diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
index c4015f30f9fa7..d0eb03ada704d 100644
--- a/net/9p/trans_fd.c
+++ b/net/9p/trans_fd.c
@@ -832,14 +832,21 @@ static int p9_fd_open(struct p9_client *client, int rfd, int wfd)
goto out_free_ts;
if (!(ts->rd->f_mode & FMODE_READ))
goto out_put_rd;
- /* prevent workers from hanging on IO when fd is a pipe */
- ts->rd->f_flags |= O_NONBLOCK;
+ /* Prevent workers from hanging on IO when fd is a pipe.
+ * It's technically possible for userspace or concurrent mounts to
+ * modify this flag concurrently, which will likely result in a
+ * broken filesystem. However, just having bad flags here should
+ * not crash the kernel or cause any other sort of bug, so mark this
+ * particular data race as intentional so that tooling (like KCSAN)
+ * can allow it and detect further problems.
+ */
+ data_race(ts->rd->f_flags |= O_NONBLOCK);
ts->wr = fget(wfd);
if (!ts->wr)
goto out_put_rd;
if (!(ts->wr->f_mode & FMODE_WRITE))
goto out_put_wr;
- ts->wr->f_flags |= O_NONBLOCK;
+ data_race(ts->wr->f_flags |= O_NONBLOCK);
client->trans = ts;
client->status = Connected;
--
2.42.0
next parent reply other threads:[~2023-11-07 23:23 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20231107232231.3775605-1-sashal@kernel.org>
2023-11-07 23:22 ` Sasha Levin [this message]
2023-11-07 23:22 ` [PATCH AUTOSEL 6.6 18/18] 9p: v9fs_listxattr: fix %s null argument warning Sasha Levin
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