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vfs: Fix potential select() race if both sock and other-fd trigger

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This fixes a potential race condition in select() if both a socket-fd
and non-socket fd trigger simultaneously to unblock this select.
In case of both fds, we use lwip's local thread semaphore, so we only
have to try return it (if it was taken/triggered more than once) when
we exit select().

Closes https://github.com/espressif/esp-idf/issues/8896
This commit is contained in:
David Cermak 2022-05-06 14:40:12 +02:00
parent ae6c52e9f9
commit f974099b42
1 changed files with 10 additions and 2 deletions
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12
components/vfs/vfs.c
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@ -1053,8 +1053,16 @@ int esp_vfs_select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *errorfds
if (ret >= 0) {
ret += set_global_fd_sets(vfs_fds_triple, vfs_count, readfds, writefds, errorfds);
}
if (sel_sem.is_sem_local && sel_sem.sem) {
vSemaphoreDelete(sel_sem.sem);
if (sel_sem.sem) { // Cleanup the select semaphore
if (sel_sem.is_sem_local) {
vSemaphoreDelete(sel_sem.sem);
} else if (socket_select) {
SemaphoreHandle_t *s = sel_sem.sem;
/* Select might have been triggered from both lwip and vfs fds at the same time, and
* we have to make sure that the lwip semaphore is cleared when we exit select().
* It is safe, as the semaphore belongs to the calling thread. */
xSemaphoreTake(*s, 0);
}
sel_sem.sem = NULL;
}
_lock_acquire(&s_fd_table_lock);