git: e4a65cff230d - stable/12 - nfsd: Limit parsing of layout errors to maxcnt bytes

The branch stable/12 has been updated by rmacklem:

URL: https://cgit.FreeBSD.org/src/commit/?id=e4a65cff230dd1e055ad1651f285e5e11b160cb8

commit e4a65cff230dd1e055ad1651f285e5e11b160cb8
Author:     Rick Macklem <rmacklem@FreeBSD.org>
AuthorDate: 2021-12-13 23:21:31 +0000
Commit:     Rick Macklem <rmacklem@FreeBSD.org>
CommitDate: 2021-12-27 01:00:57 +0000

    nfsd: Limit parsing of layout errors to maxcnt bytes
    
    This patch decrements maxcnt by the appropriate
    number of bytes during parsing and checks to see
    if there is data remaining.  If not, it just returns
    from nfsrv_flexlayouterr() without further processing.
    This prevents the tl pointer from running off the end
    of the error data pointed at by layp, if there are
    flaws in the data.
    
    PR:     260293
    
    (cherry picked from commit c302f889e21f73746a3b0917df5246e639df1481)
---
 sys/fs/nfsserver/nfs_nfsdstate.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/sys/fs/nfsserver/nfs_nfsdstate.c b/sys/fs/nfsserver/nfs_nfsdstate.c
index d9235ab783c6..882ff97e62fb 100644
--- a/sys/fs/nfsserver/nfs_nfsdstate.c
+++ b/sys/fs/nfsserver/nfs_nfsdstate.c
@@ -6969,14 +6969,25 @@ nfsrv_flexlayouterr(struct nfsrv_descript *nd, uint32_t *layp, int maxcnt,
 	char devid[NFSX_V4DEVICEID];
 
 	tl = layp;
-	cnt = fxdr_unsigned(int, *tl++);
+	maxcnt -= NFSX_UNSIGNED;
+	if (maxcnt > 0)
+		cnt = fxdr_unsigned(int, *tl++);
+	else
+		cnt = 0;
 	NFSD_DEBUG(4, "flexlayouterr cnt=%d\n", cnt);
 	for (i = 0; i < cnt; i++) {
+		maxcnt -= NFSX_STATEID + 2 * NFSX_HYPER +
+		    NFSX_UNSIGNED;
+		if (maxcnt <= 0)
+			break;
 		/* Skip offset, length and stateid for now. */
 		tl += (4 + NFSX_STATEID / NFSX_UNSIGNED);
 		errcnt = fxdr_unsigned(int, *tl++);
 		NFSD_DEBUG(4, "flexlayouterr errcnt=%d\n", errcnt);
 		for (j = 0; j < errcnt; j++) {
+			maxcnt -= NFSX_V4DEVICEID + 2 * NFSX_UNSIGNED;
+			if (maxcnt < 0)
+				break;
 			NFSBCOPY(tl, devid, NFSX_V4DEVICEID);
 			tl += (NFSX_V4DEVICEID / NFSX_UNSIGNED);
 			stat = fxdr_unsigned(int, *tl++);