<p>laforge has uploaded this change for <strong>review</strong>.</p><p><a href="https://gerrit.osmocom.org/c/libosmo-netif/+/18628">View Change</a></p><pre style="font-family: monospace,monospace; white-space: pre-wrap;">src/stream: Work around more Linux kernel ABI breakage<br><br>Back in Change-Id Ia95dd1f9ffed9f743c049e05797b1a6f1f9f8c69 we tried<br>to work-around kernel ABI breakage introduced in kernel >= v5.5, but it<br>seems that there have already been similar ABI breakages in v4.11 and v4.12.<br><br>See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/uapi/linux/sctp.h?id=b6e6b5f1da7e8d092f86a4351802c27c0170c5a5<br>and https://marc.info/?l=linux-sctp&m=158729301516157&w=2 for the ost<br>recent incarnation.<br><br>See https://osmocom.org/issues/4573#note-6 for all known cases<br>of SCTP_EVENTS ABI breakage.<br><br>Change-Id: Icc49f347cdc0bb77a5c0e230597d662ac35b4acc<br>---<br>M src/stream.c<br>1 file changed, 71 insertions(+), 20 deletions(-)<br><br></pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;">git pull ssh://gerrit.osmocom.org:29418/libosmo-netif refs/changes/28/18628/1</pre><pre style="font-family: monospace,monospace; white-space: pre-wrap;"><span>diff --git a/src/stream.c b/src/stream.c</span><br><span>index 6e4c461..6b8f5a0 100644</span><br><span>--- a/src/stream.c</span><br><span>+++ b/src/stream.c</span><br><span>@@ -73,6 +73,75 @@</span><br><span> #define MSG_NOSIGNAL 0</span><br><span> #endif</span><br><span> </span><br><span style="color: hsl(120, 100%, 40%);">+/* is any of the bytes from offset .. size in 'u8' non-zero? */</span><br><span style="color: hsl(120, 100%, 40%);">+static bool byte_nonzero(const uint8_t *u8, unsigned int offset, unsigned int u8_size)</span><br><span style="color: hsl(120, 100%, 40%);">+{</span><br><span style="color: hsl(120, 100%, 40%);">+ int j;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ for (j = offset; j < u8_size; j++) {</span><br><span style="color: hsl(120, 100%, 40%);">+ if (u8[j] != 0)</span><br><span style="color: hsl(120, 100%, 40%);">+ return true;</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ return false;</span><br><span style="color: hsl(120, 100%, 40%);">+}</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+/* Attempt to work around Linux kernel ABI breakage</span><br><span style="color: hsl(120, 100%, 40%);">+ *</span><br><span style="color: hsl(120, 100%, 40%);">+ * The Linux kernel ABI for the SCTP_EVENTS socket option has been broken repeatedly.</span><br><span style="color: hsl(120, 100%, 40%);">+ * - until commit 35ea82d611da59f8bea44a37996b3b11bb1d3fd7 ( kernel < 4.11), the size is 10 bytes</span><br><span style="color: hsl(120, 100%, 40%);">+ * - in 4.11 it is 11 bytes</span><br><span style="color: hsl(120, 100%, 40%);">+ * - in 4.12 .. 5.4 it is 13 bytes</span><br><span style="color: hsl(120, 100%, 40%);">+ * - in kernels >= 5.5 it is 14 bytes</span><br><span style="color: hsl(120, 100%, 40%);">+ *</span><br><span style="color: hsl(120, 100%, 40%);">+ * This wouldn't be a problem if the kernel didn't have a "stupid" assumption that the structure</span><br><span style="color: hsl(120, 100%, 40%);">+ * size passed by userspace will match 1:1 the length of the structure at kernel compile time. In</span><br><span style="color: hsl(120, 100%, 40%);">+ * an ideal world, it would just use the known first bytes and assume the remainder is all zero.</span><br><span style="color: hsl(120, 100%, 40%);">+ * But as it doesn't do that, let's try to work around this */</span><br><span style="color: hsl(120, 100%, 40%);">+static int sctp_setsockopt_events_linux_workaround(int fd, const struct sctp_event_subscribe *event)</span><br><span style="color: hsl(120, 100%, 40%);">+{</span><br><span style="color: hsl(120, 100%, 40%);">+ unsigned int size = sizeof(*event);</span><br><span style="color: hsl(120, 100%, 40%);">+ const uint8_t try_sizes[] = { 14, 13, 11, 10 };</span><br><span style="color: hsl(120, 100%, 40%);">+ uint8_t buf[14];</span><br><span style="color: hsl(120, 100%, 40%);">+ int rc, i;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* first try to use the userspace structure as-is */</span><br><span style="color: hsl(120, 100%, 40%);">+ rc = setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS, event, sizeof(*event));</span><br><span style="color: hsl(120, 100%, 40%);">+ if (rc != -EINVAL)</span><br><span style="color: hsl(120, 100%, 40%);">+ return rc;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* next, try with shorter sizes (older kernel + new userspace headers) */</span><br><span style="color: hsl(120, 100%, 40%);">+ for (i = 0; i < ARRAY_SIZE(try_sizes); i++) {</span><br><span style="color: hsl(120, 100%, 40%);">+ if (try_sizes[i] >= size)</span><br><span style="color: hsl(120, 100%, 40%);">+ continue;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* ensure that if the caller requested one of the "later" options we don't</span><br><span style="color: hsl(120, 100%, 40%);">+ * truncate */</span><br><span style="color: hsl(120, 100%, 40%);">+ if (byte_nonzero((const uint8_t *)event, try_sizes[i], size))</span><br><span style="color: hsl(120, 100%, 40%);">+ continue;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ rc = setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS, event, try_sizes[i]);</span><br><span style="color: hsl(120, 100%, 40%);">+ if (rc != -EINVAL)</span><br><span style="color: hsl(120, 100%, 40%);">+ return rc;</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ /* finally, try with larger sizes (newer kernel + old userspace headers) */</span><br><span style="color: hsl(120, 100%, 40%);">+ if (size < sizeof(buf)) {</span><br><span style="color: hsl(120, 100%, 40%);">+ memset(buf, 0, sizeof(buf));</span><br><span style="color: hsl(120, 100%, 40%);">+ memcpy(buf, event, size);</span><br><span style="color: hsl(120, 100%, 40%);">+ for (i = 0; i < ARRAY_SIZE(try_sizes); i++) {</span><br><span style="color: hsl(120, 100%, 40%);">+ if (try_sizes[i] < size)</span><br><span style="color: hsl(120, 100%, 40%);">+ continue;</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ rc = setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS, buf, try_sizes[i]);</span><br><span style="color: hsl(120, 100%, 40%);">+ if (rc != -EINVAL)</span><br><span style="color: hsl(120, 100%, 40%);">+ return rc;</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span style="color: hsl(120, 100%, 40%);">+ }</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span style="color: hsl(120, 100%, 40%);">+ return rc;</span><br><span style="color: hsl(120, 100%, 40%);">+}</span><br><span style="color: hsl(120, 100%, 40%);">+</span><br><span> static int sctp_sock_activate_events(int fd)</span><br><span> {</span><br><span> #ifdef HAVE_LIBSCTP</span><br><span>@@ -89,28 +158,10 @@</span><br><span> event.sctp_shutdown_event = 1;</span><br><span> /* IMPORTANT: Do NOT enable sender_dry_event here, see</span><br><span> * https://bugzilla.redhat.com/show_bug.cgi?id=1442784 */</span><br><span style="color: hsl(0, 100%, 40%);">- rc = setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS,</span><br><span style="color: hsl(0, 100%, 40%);">- &event, sizeof(event));</span><br><span> </span><br><span style="color: hsl(0, 100%, 40%);">- /*</span><br><span style="color: hsl(0, 100%, 40%);">- * Attempt to work around kernel ABI breakage</span><br><span style="color: hsl(0, 100%, 40%);">- *</span><br><span style="color: hsl(0, 100%, 40%);">- * In kernel commit b6e6b5f1da7e8d092f86a4351802c27c0170c5a5, the</span><br><span style="color: hsl(0, 100%, 40%);">- * struct sctp_event_subscribe had a u8 field added to it at the end, thus</span><br><span style="color: hsl(0, 100%, 40%);">- * breaking ABI.</span><br><span style="color: hsl(0, 100%, 40%);">- * See https://marc.info/?l=linux-sctp&m=158729301516157&w=2 for discussion.</span><br><span style="color: hsl(0, 100%, 40%);">- *</span><br><span style="color: hsl(0, 100%, 40%);">- * We attempt to work around the issue where the kernel header are new</span><br><span style="color: hsl(0, 100%, 40%);">- * and running kernel is old, by forcing the size of the struct to 13 which</span><br><span style="color: hsl(0, 100%, 40%);">- * is the "old" size</span><br><span style="color: hsl(0, 100%, 40%);">- */</span><br><span style="color: hsl(0, 100%, 40%);">- if ((rc < 0) && (sizeof(event) != 13))</span><br><span style="color: hsl(0, 100%, 40%);">- rc = setsockopt(fd, IPPROTO_SCTP, SCTP_EVENTS,</span><br><span style="color: hsl(0, 100%, 40%);">- &event, 13);</span><br><span style="color: hsl(0, 100%, 40%);">-</span><br><span style="color: hsl(120, 100%, 40%);">+ rc = sctp_setsockopt_events_linux_workaround(fd, &event);</span><br><span> if (rc < 0)</span><br><span style="color: hsl(0, 100%, 40%);">- LOGP(DLINP, LOGL_ERROR, "couldn't activate SCTP events "</span><br><span style="color: hsl(0, 100%, 40%);">- "on FD %u\n", fd);</span><br><span style="color: hsl(120, 100%, 40%);">+ LOGP(DLINP, LOGL_ERROR, "couldn't activate SCTP events on FD %u\n", fd);</span><br><span> return rc;</span><br><span> #else</span><br><span> return -1;</span><br><span></span><br></pre><p>To view, visit <a href="https://gerrit.osmocom.org/c/libosmo-netif/+/18628">change 18628</a>. 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<div style="display:none"> Gerrit-Project: libosmo-netif </div>
<div style="display:none"> Gerrit-Branch: master </div>
<div style="display:none"> Gerrit-Change-Id: Icc49f347cdc0bb77a5c0e230597d662ac35b4acc </div>
<div style="display:none"> Gerrit-Change-Number: 18628 </div>
<div style="display:none"> Gerrit-PatchSet: 1 </div>
<div style="display:none"> Gerrit-Owner: laforge <laforge@osmocom.org> </div>
<div style="display:none"> Gerrit-MessageType: newchange </div>