On 29/07/2020 03:42, Greg Kurz wrote:
> Hi Alexey,
>
> Working on 9p now ?!? ;-)
No, I am running syzkaller and seeing things :)
> Cc'ing Dominique Martinet who appears to be the person who takes care of 9p
> these days.
>
> On Tue, 28 Jul 2020 22:41:29 +1000
> Alexey Kardashevskiy <a...@ozlabs.ru> wrote:
>
>> The "fd" transport layer uses 2 file descriptors passed externally
>> and calls kernel_write()/kernel_read() on these. If files were opened
>> without FMODE_WRITE/FMODE_READ, WARN_ON_ONCE() will fire.
>>
>> This adds file mode checking in p9_fd_open; this returns -EBADF to
>> preserve the original behavior.
>>
>
> So this would cause open() to fail with EBADF, which might look a bit
> weird to userspace since it didn't pass an fd... Is this to have a
> different error than -EIO that is returned when either rfd or wfd
> doesn't point to an open file descriptor ?
This is only to preserve the existing behavior.
> If yes, why do we care ?
Without the patch, p9_fd_open() produces a kernel warning which is not
great by itself and becomes crash with panic_on_warn.
>
>> Found by syzkaller.
>>
>> Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
>> ---
>> net/9p/trans_fd.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/net/9p/trans_fd.c b/net/9p/trans_fd.c
>> index 13cd683a658a..62cdfbd01f0a 100644
>> --- a/net/9p/trans_fd.c
>> +++ b/net/9p/trans_fd.c
>> @@ -797,6 +797,7 @@ static int parse_opts(char *params, struct p9_fd_opts
>> *opts)
>>
>> static int p9_fd_open(struct p9_client *client, int rfd, int wfd)
>> {
>> + bool perm;
>> struct p9_trans_fd *ts = kzalloc(sizeof(struct p9_trans_fd),
>> GFP_KERNEL);
>> if (!ts)
>> @@ -804,12 +805,16 @@ static int p9_fd_open(struct p9_client *client, int
>> rfd, int wfd)
>>
>> ts->rd = fget(rfd);
>> ts->wr = fget(wfd);
>> - if (!ts->rd || !ts->wr) {
>> + perm = ts->rd && (ts->rd->f_mode & FMODE_READ) &&
>> + ts->wr && (ts->wr->f_mode & FMODE_WRITE);
>> + if (!ts->rd || !ts->wr || !perm) {
>> if (ts->rd)
>> fput(ts->rd);
>> if (ts->wr)
>> fput(ts->wr);
>> kfree(ts);
>> + if (!perm)
>> + return -EBADF;
>> return -EIO;
>> }
>>
>
--
Alexey
