git: 5f5a45463ea0 - stable/12 - pf: Fix incorrect fragment handling

[Kristof Provost]

The branch stable/12 has been updated by kp:

URL: https://cgit.FreeBSD.org/src/commit/?id=5f5a45463ea068983092588ab897602f7aea328b

commit 5f5a45463ea068983092588ab897602f7aea328b
Author:     Kristof Provost <kp at FreeBSD.org>
AuthorDate: 2021-02-25 07:07:36 +0000
Commit:     Kristof Provost <kp at FreeBSD.org>
CommitDate: 2021-02-28 15:37:07 +0000

    pf: Fix incorrect fragment handling
    
    A sequence of overlapping IPv4 fragments could crash the kernel in
    pf due to an assertion.
    
    Reported by:    Alexander Bluhm
    Obtained from:  OpenBSD
    MFC after:      3 days
    Sponsored by:   Rubicon Communications, LLC ("Netgate")
    
    (cherry picked from commit 5f1b1f184b7f12330cf4a027e3db7c6700c67640)
---
 sys/netpfil/pf/pf_norm.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/sys/netpfil/pf/pf_norm.c b/sys/netpfil/pf/pf_norm.c
index 0770fcfd4c58..2a3c1d442fd4 100644
--- a/sys/netpfil/pf/pf_norm.c
+++ b/sys/netpfil/pf/pf_norm.c
@@ -545,6 +545,7 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 	struct pf_frent		*after, *next, *prev;
 	struct pf_fragment	*frag;
 	uint16_t		total;
+	int			old_index, new_index;
 
 	PF_FRAG_ASSERT();
 
@@ -656,8 +657,30 @@ pf_fillup_fragment(struct pf_fragment_cmp *key, struct pf_frent *frent,
 		DPFPRINTF(("adjust overlap %d", aftercut));
 		if (aftercut < after->fe_len) {
 			m_adj(after->fe_m, aftercut);
+			old_index = pf_frent_index(after);
 			after->fe_off += aftercut;
 			after->fe_len -= aftercut;
+			new_index = pf_frent_index(after);
+			if (old_index != new_index) {
+				DPFPRINTF(("frag index %d, new %d",
+				    old_index, new_index));
+				/* Fragment switched queue as fe_off changed */
+				after->fe_off -= aftercut;
+				after->fe_len += aftercut;
+				/* Remove restored fragment from old queue */
+				pf_frent_remove(frag, after);
+				after->fe_off += aftercut;
+				after->fe_len -= aftercut;
+				/* Insert into correct queue */
+				if (pf_frent_insert(frag, after, prev)) {
+					DPFPRINTF(
+					    ("fragment requeue limit exceeded"));
+					m_freem(after->fe_m);
+					uma_zfree(V_pf_frent_z, after);
+					/* There is not way to recover */
+					goto bad_fragment;
+				}
+			}
 			break;
 		}