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Protect uses of select() from crash on too many file descriptors #119

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Protect uses of select() from crash on too many file descriptors #119

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29 changes: 27 additions & 2 deletions eloop.c
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Original file line number Diff line number Diff line change
Expand Up @@ -180,6 +180,17 @@ static void eloop_sock_table_remove_sock(struct eloop_sock_table *table,
}


static inline void warn_too_many_fds()
{
static bool warned = false;

if (!warned) {
fprintf(stderr, "unable to handle more than %d file descriptors\n", FD_SETSIZE);
fprintf(stderr, "too many interfaces being watched\n");
warned = true;
}
}

static void eloop_sock_table_set_fds(struct eloop_sock_table *table,
fd_set *fds)
{
Expand All @@ -190,8 +201,13 @@ static void eloop_sock_table_set_fds(struct eloop_sock_table *table,
if (table->table == NULL)
return;

for (i = 0; i < table->count; i++)
for (i = 0; i < table->count; i++) {
if (table->table[i].sock >= FD_SETSIZE) {
warn_too_many_fds();
continue;
}
FD_SET(table->table[i].sock, fds);
}
}


Expand All @@ -205,6 +221,9 @@ static void eloop_sock_table_dispatch(struct eloop_sock_table *table,

table->changed = 0;
for (i = 0; i < table->count; i++) {
if (table->table[i].sock >= FD_SETSIZE) {
return;
}
if (FD_ISSET(table->table[i].sock, fds)) {
table->table[i].handler(table->table[i].sock,
table->table[i].eloop_data,
Expand Down Expand Up @@ -497,7 +516,8 @@ void eloop_run(void)
eloop_sock_table_set_fds(&eloop.readers, rfds);
eloop_sock_table_set_fds(&eloop.writers, wfds);
eloop_sock_table_set_fds(&eloop.exceptions, efds);
res = select(eloop.max_sock + 1, rfds, wfds, efds,
res = select(eloop.max_sock < FD_SETSIZE ? eloop.max_sock + 1 : FD_SETSIZE,
rfds, wfds, efds,
eloop.timeout ? &_tv : NULL);
if (res < 0 && errno != EINTR && errno != 0) {
perror("select");
Expand Down Expand Up @@ -571,6 +591,11 @@ void eloop_wait_for_read_sock(int sock)
if (sock < 0)
return;

if (sock >= FD_SETSIZE) {
warn_too_many_fds();
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@apconole apconole Jan 8, 2025

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I'm okay with this being added, but a quick grep through the code doesn't seem to find any in-tree callers for eloop_wait_for_read_sock.

Maybe we should delete it instead?

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@penguin359 penguin359 Jan 17, 2025 •
edited
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Yes, I only see eloop_register_read_sock() and eloop_unregister_read_sock() used, but not eloop_wait_for_read_sock(). Also, it looks like eloop_register_sock(), eloop_unregister_sock(), and os_get_time() can all be made static.

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@penguin359 penguin359 Jan 17, 2025

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Actually, I found several things to clean-up in eloop.c/eloop.h including function prototypes in the header files that refer to functions that have never existed in the Git history. I'll save that clean-up for another PR, but I think I can drop that function for now.

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@apconole apconole Feb 10, 2025

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If you are okay with it, I'll merge this patch and backport it to the 1.1 branch.

return;
}

FD_ZERO(&rfds);
FD_SET(sock, &rfds);
select(sock + 1, &rfds, NULL, NULL, NULL);
Expand Down