CVE-2021-44142: libadouble: harden parsing code

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14914

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>

2 files changed, 101 insertions, 17 deletions

diff --git a/selftest/knownfail.d/samba.unittests.adouble b/selftest/knownfail.d/samba.unittests.adouble
deleted file mode 100644
index 8b0314f2fae..00000000000
--- a/selftest/knownfail.d/samba.unittests.adouble
+++ /dev/null
@@ -1,3 +0,0 @@
-^samba.unittests.adouble.parse_abouble_finderinfo2\(none\)
-^samba.unittests.adouble.parse_abouble_finderinfo3\(none\)
-^samba.unittests.adouble.parse_abouble_date2\(none\)
diff --git a/source3/lib/adouble.c b/source3/lib/adouble.c
index 48621feb530..bb94a45e2de 100644
--- a/source3/lib/adouble.c
+++ b/source3/lib/adouble.c
@@ -269,6 +269,95 @@ size_t ad_setentryoff(struct adouble *ad, int eid, size_t off)
 	return ad->ad_eid[eid].ade_off = off;
 }
 
+/*
+ * All entries besides FinderInfo and resource fork must fit into the
+ * buffer. FinderInfo is special as it may be larger then the default 32 bytes
+ * if it contains marshalled xattrs, which we will fixup that in
+ * ad_convert(). The first 32 bytes however must also be part of the buffer.
+ *
+ * The resource fork is never accessed directly by the ad_data buf.
+ */
+static bool ad_entry_check_size(uint32_t eid,
+				size_t bufsize,
+				uint32_t off,
+				uint32_t got_len)
+{
+	struct {
+		off_t expected_len;
+		bool fixed_size;
+		bool minimum_size;
+	} ad_checks[] = {
+		[ADEID_DFORK] = {-1, false, false}, /* not applicable */
+		[ADEID_RFORK] = {-1, false, false}, /* no limit */
+		[ADEID_NAME] = {ADEDLEN_NAME, false, false},
+		[ADEID_COMMENT] = {ADEDLEN_COMMENT, false, false},
+		[ADEID_ICONBW] = {ADEDLEN_ICONBW, true, false},
+		[ADEID_ICONCOL] = {ADEDLEN_ICONCOL, false, false},
+		[ADEID_FILEI] = {ADEDLEN_FILEI, true, false},
+		[ADEID_FILEDATESI] = {ADEDLEN_FILEDATESI, true, false},
+		[ADEID_FINDERI] = {ADEDLEN_FINDERI, false, true},
+		[ADEID_MACFILEI] = {ADEDLEN_MACFILEI, true, false},
+		[ADEID_PRODOSFILEI] = {ADEDLEN_PRODOSFILEI, true, false},
+		[ADEID_MSDOSFILEI] = {ADEDLEN_MSDOSFILEI, true, false},
+		[ADEID_SHORTNAME] = {ADEDLEN_SHORTNAME, false, false},
+		[ADEID_AFPFILEI] = {ADEDLEN_AFPFILEI, true, false},
+		[ADEID_DID] = {ADEDLEN_DID, true, false},
+		[ADEID_PRIVDEV] = {ADEDLEN_PRIVDEV, true, false},
+		[ADEID_PRIVINO] = {ADEDLEN_PRIVINO, true, false},
+		[ADEID_PRIVSYN] = {ADEDLEN_PRIVSYN, true, false},
+		[ADEID_PRIVID] = {ADEDLEN_PRIVID, true, false},
+	};
+
+	if (eid >= ADEID_MAX) {
+		return false;
+	}
+	if (got_len == 0) {
+		/* Entry present, but empty, allow */
+		return true;
+	}
+	if (ad_checks[eid].expected_len == 0) {
+		/*
+		 * Shouldn't happen: implicitly initialized to zero because
+		 * explicit initializer missing.
+		 */
+		return false;
+	}
+	if (ad_checks[eid].expected_len == -1) {
+		/* Unused or no limit */
+		return true;
+	}
+	if (ad_checks[eid].fixed_size) {
+		if (ad_checks[eid].expected_len != got_len) {
+			/* Wrong size fo fixed size entry. */
+			return false;
+		}
+	} else {
+		if (ad_checks[eid].minimum_size) {
+			if (got_len < ad_checks[eid].expected_len) {
+				/*
+				 * Too small for variable sized entry with
+				 * minimum size.
+				 */
+				return false;
+			}
+		} else {
+			if (got_len > ad_checks[eid].expected_len) {
+				/* Too big for variable sized entry. */
+				return false;
+			}
+		}
+	}
+	if (off + got_len < off) {
+		/* wrap around */
+		return false;
+	}
+	if (off + got_len > bufsize) {
+		/* overflow */
+		return false;
+	}
+	return true;
+}
+
 /**
  * Return a pointer to an AppleDouble entry
  *
@@ -276,8 +365,15 @@ size_t ad_setentryoff(struct adouble *ad, int eid, size_t off)
  **/
 char *ad_get_entry(const struct adouble *ad, int eid)
 {
+	size_t bufsize = talloc_get_size(ad->ad_data);
 	off_t off = ad_getentryoff(ad, eid);
 	size_t len = ad_getentrylen(ad, eid);
+	bool valid;
+
+	valid = ad_entry_check_size(eid, bufsize, off, len);
+	if (!valid) {
+		return NULL;
+	}
 
 	if (off == 0 || len == 0) {
 		return NULL;
@@ -914,20 +1010,11 @@ static bool ad_unpack(struct adouble *ad, const size_t nentries,
 			return false;
 		}
 
-		/*
-		 * All entries besides FinderInfo and resource fork
-		 * must fit into the buffer. FinderInfo is special as
-		 * it may be larger then the default 32 bytes (if it
-		 * contains marshalled xattrs), but we will fixup that
-		 * in ad_convert(). And the resource fork is never
-		 * accessed directly by the ad_data buf (also see
-		 * comment above) anyway.
-		 */
-		if ((eid != ADEID_RFORK) &&
-		    (eid != ADEID_FINDERI) &&
-		    ((off + len) > bufsize)) {
-			DEBUG(1, ("bogus eid %d: off: %" PRIu32 ", len: %" PRIu32 "\n",
-				  eid, off, len));
+		ok = ad_entry_check_size(eid, bufsize, off, len);
+		if (!ok) {
+			DBG_ERR("bogus eid [%"PRIu32"] bufsize [%zu] "
+				"off [%"PRIu32"] len [%"PRIu32"]\n",
+				eid, bufsize, off, len);
 			return false;
 		}