Re: [PATCH 2/3] net/scm: cleanup scm_detach_fds

Ido Schimmel
2020-05-13T09:29:25Z

On Mon, May 11, 2020 at 01:59:12PM +0200, Christoph Hellwig wrote:
> Factor out two helpes to keep the code tidy.
>
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Christoph,

After installing net-next (fb9f2e92864f) on a Fedora 32 machine I cannot
ssh to it. Bisected it to this commit [1].

When trying to connect I see these error messages in journal:

sshd[1029]: error: mm_receive_fd: no message header
sshd[1029]: fatal: mm_pty_allocate: receive fds failed
sshd[1029]: fatal: mm_request_receive_expect: buffer error: incomplete message
sshd[1018]: fatal: mm_request_receive: read: Connection reset by peer

Please let me know if more info is required. I can easily test a patch
if you need me to try something.

Thanks

[1]
git bisect start
# bad: [fb9f2e92864f51d25e790947cca2ac4426a12f9c] net: dsa: tag_sja1105: appease sparse checks for ethertype accessors
git bisect bad fb9f2e92864f51d25e790947cca2ac4426a12f9c
# good: [3242956bd610af40e884b530b6c6f76f5bf85f3b] Merge branch 'net-dsa-Constify-two-tagger-ops'
git bisect good 3242956bd610af40e884b530b6c6f76f5bf85f3b
# bad: [1b0cde4091877cd7fe4b29f67645cc391b86c9ca] sfc: siena_check_caps() can be static
git bisect bad 1b0cde4091877cd7fe4b29f67645cc391b86c9ca
# bad: [cba155d591aa28689332bc568632d2f868690be1] ionic: add support for more xcvr types
git bisect bad cba155d591aa28689332bc568632d2f868690be1
# bad: [97cf0ef9305bba857f04b914fd59e83813f1eae2] Merge branch 'improve-msg_control-kernel-vs-user-pointer-handling'
git bisect bad 97cf0ef9305bba857f04b914fd59e83813f1eae2
# bad: [2618d530dd8b7ac0fdcb83f4c95b88f7b0d37ce6] net/scm: cleanup scm_detach_fds
git bisect bad 2618d530dd8b7ac0fdcb83f4c95b88f7b0d37ce6
# good: [0462b6bdb6445b887b8896f28be92e0d94c92e7b] net: add a CMSG_USER_DATA macro
git bisect good 0462b6bdb6445b887b8896f28be92e0d94c92e7b
# first bad commit: [2618d530dd8b7ac0fdcb83f4c95b88f7b0d37ce6] net/scm: cleanup scm_detach_fds

> ---
> net/core/scm.c | 94 +++++++++++++++++++++++++++-----------------------
> 1 file changed, 51 insertions(+), 43 deletions(-)
>
> diff --git a/net/core/scm.c b/net/core/scm.c
> index abfdc85a64c1b..168b006a52ff9 100644
> --- a/net/core/scm.c
> +++ b/net/core/scm.c
> @@ -277,78 +277,86 @@ void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_inter
> }
> EXPORT_SYMBOL(put_cmsg_scm_timestamping);
>
> +static int __scm_install_fd(struct file *file, int __user *ufd, int o_flags)
> +{
> + struct socket *sock;
> + int new_fd;
> + int error;
> +
> + error = security_file_receive(file);
> + if (error)
> + return error;
> +
> + new_fd = get_unused_fd_flags(o_flags);
> + if (new_fd < 0)
> + return new_fd;
> +
> + error = put_user(new_fd, ufd);
> + if (error) {
> + put_unused_fd(new_fd);
> + return error;
> + }
> +
> + /* Bump the usage count and install the file. */
> + sock = sock_from_file(file, &error);
> + if (sock) {
> + sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> + sock_update_classid(&sock->sk->sk_cgrp_data);
> + }
> + fd_install(new_fd, get_file(file));
> + return error;
> +}
> +
> +static int scm_max_fds(struct msghdr *msg)
> +{
> + if (msg->msg_controllen <= sizeof(struct cmsghdr))
> + return 0;
> + return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
> +}
> +
> void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
> {
> struct cmsghdr __user *cm
> = (__force struct cmsghdr __user*)msg->msg_control;
> -
> - int fdmax = 0;
> - int fdnum = scm->fp->count;
> - struct file **fp = scm->fp->fp;
> - int __user *cmfptr;
> + int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
> + int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
> + int __user *cmsg_data = CMSG_USER_DATA(cm);
> int err = 0, i;
>
> - if (MSG_CMSG_COMPAT & msg->msg_flags) {
> + if (msg->msg_flags & MSG_CMSG_COMPAT) {
> scm_detach_fds_compat(msg, scm);
> return;
> }
>
> - if (msg->msg_controllen > sizeof(struct cmsghdr))
> - fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
> - / sizeof(int));
> -
> - if (fdnum < fdmax)
> - fdmax = fdnum;
> -
> - for (i=0, cmfptr =(int __user *)CMSG_USER_DATA(cm); i<fdmax;
> - i++, cmfptr++)
> - {
> - struct socket *sock;
> - int new_fd;
> - err = security_file_receive(fp[i]);
> + for (i = 0; i < fdmax; i++) {
> + err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags);
> if (err)
> break;
> - err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
> - ? O_CLOEXEC : 0);
> - if (err < 0)
> - break;
> - new_fd = err;
> - err = put_user(new_fd, cmfptr);
> - if (err) {
> - put_unused_fd(new_fd);
> - break;
> - }
> - /* Bump the usage count and install the file. */
> - sock = sock_from_file(fp[i], &err);
> - if (sock) {
> - sock_update_netprioidx(&sock->sk->sk_cgrp_data);
> - sock_update_classid(&sock->sk->sk_cgrp_data);
> - }
> - fd_install(new_fd, get_file(fp[i]));
> }
>
> - if (i > 0)
> - {
> - int cmlen = CMSG_LEN(i*sizeof(int));
> + if (i > 0) {
> + int cmlen = CMSG_LEN(i * sizeof(int));
> +
> err = put_user(SOL_SOCKET, &cm->cmsg_level);
> if (!err)
> err = put_user(SCM_RIGHTS, &cm->cmsg_type);
> if (!err)
> err = put_user(cmlen, &cm->cmsg_len);
> if (!err) {
> - cmlen = CMSG_SPACE(i*sizeof(int));
> + cmlen = CMSG_SPACE(i * sizeof(int));
> if (msg->msg_controllen < cmlen)
> cmlen = msg->msg_controllen;
> msg->msg_control += cmlen;
> msg->msg_controllen -= cmlen;
> }
> }
> - if (i < fdnum || (fdnum && fdmax <= 0))
> +
> + if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
> msg->msg_flags |= MSG_CTRUNC;
>
> /*
> - * All of the files that fit in the message have had their
> - * usage counts incremented, so we just free the list.
> + * All of the files that fit in the message have had their usage counts
> + * incremented, so we just free the list.
> */
> __scm_destroy(scm);
> }
> --
> 2.26.2
>