Require update permission for the large object written by lo_put().

tglsfdc · tglsfdc · commit f1cda6d6cbb2 · 2017-08-07T10:19:22.000-04:00
lo_put() surely should require UPDATE permission, the same as lowrite(), but it failed to check for that, as reported by Chapman Flack. Oversight in commit c50b7c0; backpatch to 9.4 where that was introduced. Tom Lane and Michael Paquier Security: CVE-2017-7548
diff --git a/src/backend/libpq/be-fsstubs.c b/src/backend/libpq/be-fsstubs.c
@@ -898,6 +898,18 @@ lo_put(PG_FUNCTION_ARGS)
 	CreateFSContext();
 
 	loDesc = inv_open(loOid, INV_WRITE, fscxt);
+
+	/* Permission check */
+	if (!lo_compat_privileges &&
+		pg_largeobject_aclcheck_snapshot(loDesc->id,
+										 GetUserId(),
+										 ACL_UPDATE,
+										 loDesc->snapshot) != ACLCHECK_OK)
+		ereport(ERROR,
+				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
+				 errmsg("permission denied for large object %u",
+						loDesc->id)));
+
 	inv_seek(loDesc, offset, SEEK_SET);
 	written = inv_write(loDesc, VARDATA_ANY(str), VARSIZE_ANY_EXHDR(str));
 	Assert(written == VARSIZE_ANY_EXHDR(str));
diff --git a/src/test/regress/expected/privileges.out b/src/test/regress/expected/privileges.out
@@ -1189,6 +1189,14 @@ SELECT lo_create(2002);
       2002
 (1 row)
 
+SELECT loread(lo_open(1001, x'20000'::int), 32);	-- allowed, for now
+ loread 
+--------
+ \x
+(1 row)
+
+SELECT lowrite(lo_open(1001, x'40000'::int), 'abcd');	-- fail, wrong mode
+ERROR:  large object descriptor 0 was not opened for writing
 SELECT loread(lo_open(1001, x'40000'::int), 32);
  loread 
 --------
@@ -1284,6 +1292,8 @@ SELECT lowrite(lo_open(1002, x'20000'::int), 'abcd');	-- to be denied
 ERROR:  permission denied for large object 1002
 SELECT lo_truncate(lo_open(1002, x'20000'::int), 10);	-- to be denied
 ERROR:  permission denied for large object 1002
+SELECT lo_put(1002, 1, 'abcd');				-- to be denied
+ERROR:  permission denied for large object 1002
 SELECT lo_unlink(1002);					-- to be denied
 ERROR:  must be owner of large object 1002
 SELECT lo_export(1001, '/dev/null');			-- to be denied
diff --git a/src/test/regress/sql/privileges.sql b/src/test/regress/sql/privileges.sql
@@ -753,6 +753,9 @@ SET SESSION AUTHORIZATION regressuser2;
 SELECT lo_create(2001);
 SELECT lo_create(2002);
 
+SELECT loread(lo_open(1001, x'20000'::int), 32);	-- allowed, for now
+SELECT lowrite(lo_open(1001, x'40000'::int), 'abcd');	-- fail, wrong mode
+
 SELECT loread(lo_open(1001, x'40000'::int), 32);
 SELECT loread(lo_open(1002, x'40000'::int), 32);	-- to be denied
 SELECT loread(lo_open(1003, x'40000'::int), 32);
@@ -792,6 +795,7 @@ SET SESSION AUTHORIZATION regressuser4;
 SELECT loread(lo_open(1002, x'40000'::int), 32);	-- to be denied
 SELECT lowrite(lo_open(1002, x'20000'::int), 'abcd');	-- to be denied
 SELECT lo_truncate(lo_open(1002, x'20000'::int), 10);	-- to be denied
+SELECT lo_put(1002, 1, 'abcd');				-- to be denied
 SELECT lo_unlink(1002);					-- to be denied
 SELECT lo_export(1001, '/dev/null');			-- to be denied
 
