lib/posix-poll: Fix vfscore files w/o epoll support

This change makes epoll correctly handle vfscore files that do not
support being polled, such as filesystem files. Previously these would
be silently ignored, leading to hangs in epoll_wait.
Now epoll_ctl correctly errors out with -EPERM when attempting to
register a file descriptor from an unpollable vfscore file.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Ioan-Teodor Teugea <ioan_teodor.teugea@stud.acs.upb.ro>
Reviewed-by: Mihnea Firoiu <mihneafiroiu0@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
GitHub-Closes: #1258

diff --git a/lib/posix-poll/epoll.c b/lib/posix-poll/epoll.c
index c7f65834fee47b7cda320b59c58d7ee4db39301f..46325b0b8f9197705dfc13c396801c11ede0069e 100644 (file)
--- a/lib/posix-poll/epoll.c
+++ b/lib/posix-poll/epoll.c
@@ -123,20 +123,18 @@ static int vfs_poll(struct vfscore_file *vfd, unsigned int *revents,
        return VOP_POLL(vnode, revents, ecb);
 }
 
-static void vfs_poll_register(struct vfscore_file *vfd,
-                             struct epoll_legacy *leg)
+static int vfs_poll_register(struct vfscore_file *vfd, struct epoll_legacy *leg)
 {
-       int ret;
+       int ret = vfs_poll(vfd, &leg->revents, &leg->ecb);
 
-       ret = vfs_poll(vfd, &leg->revents, &leg->ecb);
-       if (unlikely(ret)) {
-               leg->revents = EPOLLERR;
-       } else {
-               uk_list_add_tail(&leg->f_link, &vfd->f_ep);
-               (void)uk_and(&leg->revents, leg->mask);
-               if (leg->revents)
-                       uk_file_event_set(leg->epf, UKFD_POLLIN);
-       }
+       if (unlikely(ret))
+               return -ret; /* vfscore uses positive errnos */
+
+       uk_list_add_tail(&leg->f_link, &vfd->f_ep);
+       (void)uk_and(&leg->revents, leg->mask);
+       if (leg->revents)
+               uk_file_event_set(leg->epf, UKFD_POLLIN);
+       return 0;
 }
 #endif /* CONFIG_LIBVFSCORE */
 
@@ -242,6 +240,7 @@ static int epoll_add_legacy(const struct uk_file *epf,
 {
        struct epoll_alloc *al = __containerof(epf, struct epoll_alloc, f);
        struct epoll_entry *ent;
+       int r;
 
        /* New entry */
        ent = uk_malloc(al->alloc, sizeof(*ent));
@@ -263,10 +262,17 @@ static int epoll_add_legacy(const struct uk_file *epf,
        };
        UK_INIT_LIST_HEAD(&ent->legacy_cb.ecb.cb_link);
        UK_INIT_LIST_HEAD(&ent->legacy_cb.f_link);
-       *tail = ent;
        /* Poll, register & update if needed */
-       vfs_poll_register(vf, &ent->legacy_cb);
+       r = vfs_poll_register(vf, &ent->legacy_cb);
+       if (unlikely(r)) {
+               uk_free(al->alloc, ent);
+               if (r == -EINVAL)
+                       return -EPERM;
+               else
+                       return r;
+       }
 
+       *tail = ent;
        return 0;
 }
 #endif /* CONFIG_LIBVFSCORE */