git: c46697b9cb97 - main - freebsd32_sendmsg: fix control message ABI

[Brooks Davis]

The branch main has been updated by brooks:

URL: 
https://cgit.FreeBSD.org/src/commit/?id=c46697b9cb97a14f61ac0a58758aab081b9e48c5

commit c46697b9cb97a14f61ac0a58758aab081b9e48c5
Author:     Brooks Davis <bro...@freebsd.org>
AuthorDate: 2022-08-24 17:34:39 +0000
Commit:     Brooks Davis <bro...@freebsd.org>
CommitDate: 2022-08-24 17:34:39 +0000

    freebsd32_sendmsg: fix control message ABI
    
    When a freebsd32 caller uses all or most allowed space for control
    messages (MCLBYTES == 2K) then the message may no longer fit when
    the messages are padded for 64-bit alignment.  Historically we've just
    shrugged and said there is no ABI guarantee.  We ran into this on
    CheriBSD where a capsicumized 64-bit nm would fail when called with more
    than 64 files.
    
    Fix this by not gratutiously capping size of mbuf data we'll allocate
    to MCLBYTES and let m_get2 allocate up to MJUMPAGESIZE (4K or larger).
    Instead of hard-coding a length check, let m_get2 do it and check for a
    NULL return.
    
    Reviewed by:    markj, jhb, emaste
    Sponsored by:   DARPA, AFRL
    Differential Revision:  https://reviews.freebsd.org/D36322
---
 sys/compat/freebsd32/freebsd32_misc.c | 21 +++++++++++----------
 1 file changed, 11 insertions(+), 10 deletions(-)

diff --git a/sys/compat/freebsd32/freebsd32_misc.c 
b/sys/compat/freebsd32/freebsd32_misc.c
index d1c44a4f9952..b4c212ecd38d 100644
--- a/sys/compat/freebsd32/freebsd32_misc.c
+++ b/sys/compat/freebsd32/freebsd32_misc.c
@@ -1535,6 +1535,7 @@ freebsd32_copyin_control(struct mbuf **mp, caddr_t buf, 
u_int buflen)
        u_int msglen, outlen;
        int error;
 
+       /* Enforce the size limit of the native implementation. */
        if (buflen > MCLBYTES)
                return (EINVAL);
 
@@ -1570,20 +1571,20 @@ freebsd32_copyin_control(struct mbuf **mp, caddr_t buf, 
u_int buflen)
                outlen += CMSG_ALIGN(sizeof(*cm)) +
                    CMSG_ALIGN(msglen - FREEBSD32_ALIGN(sizeof(*cm)));
        }
-       if (error == 0 && outlen > MCLBYTES) {
-               /*
-                * XXXMJ This implies that the upper limit on 32-bit aligned
-                * control messages is less than MCLBYTES, and so we are not
-                * perfectly compatible.  However, there is no platform
-                * guarantee that mbuf clusters larger than MCLBYTES can be
-                * allocated.
-                */
-               error = EINVAL;
-       }
        if (error != 0)
                goto out;
 
+       /*
+        * Allocate up to MJUMPAGESIZE space for the re-aligned and
+        * re-padded control messages.  This allows a full MCLBYTES of
+        * 32-bit sized and aligned messages to fit and avoids an ABI
+        * mismatch with the native implementation.
+        */
        m = m_get2(outlen, M_WAITOK, MT_CONTROL, 0);
+       if (m == NULL) {
+               error = EINVAL;
+               goto out;
+       }
        m->m_len = outlen;
        md = mtod(m, void *);