From f80a5b0ed0a00b3946e2ee85b52dbb537c2fe985 Mon Sep 17 00:00:00 2001 From: Colin Cross Date: Thu, 9 Feb 2023 14:50:49 -0800 Subject: [PATCH] Increase sendmsg internal buffer to support SCM_MAX_FD The kernel defines a limit on the number of fds that can be passed through an SCM_RIGHTS ancillary message as SCM_MAX_FD. The value was 255 before kernel 2.6.38 (after that it is 253), and an SCM_RIGHTS ancillary message with 255 fds requires 1040 bytes, slightly more than the current 1024 byte internal buffer in sendmsg. 1024 is an arbitrary size, so increase it to match the the arbitrary size limit in the kernel. This fixes tests that are verifying they support up to SCM_MAX_FD fds. --- src/network/sendmsg.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/src/network/sendmsg.c b/src/network/sendmsg.c index 80cc5f41..dad3814f 100644 --- a/src/network/sendmsg.c +++ b/src/network/sendmsg.c @@ -8,13 +8,16 @@ ssize_t sendmsg(int fd, const struct msghdr *msg, int flags) { #if LONG_MAX > INT_MAX struct msghdr h; - struct cmsghdr chbuf[1024/sizeof(struct cmsghdr)+1], *c; + /* Kernels before 2.6.38 set SCM_MAX_FD to 255, allocate enough + * space to support an SCM_RIGHTS ancillary message with 255 fds. + * Kernels since 2.6.38 set SCM_MAX_FD to 253. */ + struct cmsghdr chbuf[CMSG_SPACE(255*sizeof(int))/sizeof(struct cmsghdr)+1], *c; if (msg) { h = *msg; h.__pad1 = h.__pad2 = 0; msg = &h; if (h.msg_controllen) { - if (h.msg_controllen > 1024) { + if (h.msg_controllen > sizeof(chbuf)) { errno = ENOMEM; return -1; } -- 2.39.1.581.gbfd45094c4-goog