The standard approach for using variable values in SQLite queries is the "question mark style", like this:
import sqlite3
with sqlite3.connect(":memory:") as connection:
connection.execute("CREATE TABLE foo(bar)")
connection.execute("INSERT INTO foo(bar) VALUES (?)", ("cow",))
print(list(connection.execute("SELECT * from foo")))
# prints [(u'cow',)]
However, this only works for substituting values into queries. It fails when used for table or column names:
import sqlite3
with sqlite3.connect(":memory:") as connection:
connection.execute("CREATE TABLE foo(?)", ("bar",))
# raises sqlite3.OperationalError: near "?": syntax error
Neither the sqlite3 module nor PEP 249 mention a function for escaping names or values. Presumably this is to discourage users from assembling their queries with strings, but it leaves me at a loss.
What function or technique is most appropriate for using variable names for columns or tables in SQLite? I'd would strongly prefer to do able to do this without any other dependencies, since I'll be using it in my own wrapper.
I looked for but couldn't find a clear and complete description of the relevant part of SQLite's syntax, to use to write my own function. I want to be sure this will work for any identifier permitted by SQLite, so a trial-and-error solution is too uncertain for me.
SQLite uses " to quote identifiers but I'm not sure that just escaping them is sufficient. PHP's sqlite_escape_string function's documentation suggests that certain binary data may need to be escaped as well, but that may be a quirk of the PHP library.
To convert any string into a SQLite identifier:
Ensure the string can be encoded as UTF-8.
Ensure the string does not include any NUL characters.
Replace all " with "".
Wrap the entire thing in double quotes.
Implementation
import codecs
def quote_identifier(s, errors="strict"):
encodable = s.encode("utf-8", errors).decode("utf-8")
nul_index = encodable.find("\x00")
if nul_index >= 0:
error = UnicodeEncodeError("NUL-terminated utf-8", encodable,
nul_index, nul_index + 1, "NUL not allowed")
error_handler = codecs.lookup_error(errors)
replacement, _ = error_handler(error)
encodable = encodable.replace("\x00", replacement)
return "\"" + encodable.replace("\"", "\"\"") + "\""
Given a string single argument, it will escape and quote it correctly or raise an exception. The second argument can be used to specify any error handler registered in the codecs module. The built-in ones are:
'strict': raise an exception in case of an encoding error
'replace': replace malformed data with a suitable replacement marker, such as '?' or '\ufffd'
'ignore': ignore malformed data and continue without further notice
'xmlcharrefreplace': replace with the appropriate XML character reference (for encoding only)
'backslashreplace': replace with backslashed escape sequences (for encoding only)
This doesn't check for reserved identifiers, so if you try to create a new SQLITE_MASTER table it won't stop you.
Example Usage
import sqlite3
def test_identifier(identifier):
"Tests an identifier to ensure it's handled properly."
with sqlite3.connect(":memory:") as c:
c.execute("CREATE TABLE " + quote_identifier(identifier) + " (foo)")
assert identifier == c.execute("SELECT name FROM SQLITE_MASTER").fetchone()[0]
test_identifier("'Héllo?'\\\n\r\t\"Hello!\" -☃") # works
test_identifier("北方话") # works
test_identifier(chr(0x20000)) # works
print(quote_identifier("Fo\x00o!", "replace")) # prints "Fo?o!"
print(quote_identifier("Fo\x00o!", "ignore")) # prints "Foo!"
print(quote_identifier("Fo\x00o!")) # raises UnicodeEncodeError
print(quote_identifier(chr(0xD800))) # raises UnicodeEncodeError
Observations and References
SQLite identifiers are TEXT, not binary.
SQLITE_MASTER schema in the FAQ
Python 2 SQLite API yelled at me when I gave it bytes it couldn't decode as text.
Python 3 SQLite API requires queries be strs, not bytes.
SQLite identifiers are quoted using double-quotes.
SQL as Understood by SQLite
Double-quotes in SQLite identifiers are escaped as two double quotes.
SQLite identifiers preserve case, but they are case-insensitive towards ASCII letters. It is possible to enable unicode-aware case-insensitivity.
SQLite FAQ Question #18
SQLite does not support the NUL character in strings or identifiers.
SQLite Ticket 57c971fc74
sqlite3 can handle any other unicode string as long as it can be properly encoded to UTF-8. Invalid strings could cause crashes between Python 3.0 and Python 3.1.2 or thereabouts. Python 2 accepted these invalid strings, but this is considered a bug.
Python Issue #12569
Modules/_sqlite/cursor.c
I tested it a bunch.
The psycopg2 documentation explicitly recommends using normal python % or {} formatting to substitute in table and column names (or other bits of dynamic syntax), and then using the parameter mechanism to substitute values into the query.
I disagree with everyone who is saying "don't ever use dynamic table/column names, you're doing something wrong if you need to". I write programs to automate stuff with databases every day, and I do it all the time. We have lots of databases with lots of tables, but they are all built on repeated patterns, so generic code to handle them is extremely useful. Hand-writing the queries every time would be far more error prone and dangerous.
It comes down to what "safe" means. The conventional wisdom is that using normal python string manipulation to put values into your queries is not "safe". This is because there are all sorts of things that can go wrong if you do that, and such data very often comes from the user and is not in your control. You need a 100% reliable way of escaping these values properly so that a user cannot inject SQL in a data value and have the database execute it. So the library writers do this job; you never should.
If, however, you're writing generic helper code to operate on things in databases, then these considerations don't apply as much. You are implicitly giving anyone who can call such code access to everything in the database; that's the point of the helper code. So now the safety concern is making sure that user-generated data can never be used in such code. This is a general security issue in coding, and is just the same problem as blindly execing a user-input string. It's a distinct issue from inserting values into your queries, because there you want to be able to safely handle user-input data.
So my recommendation is: do whatever you want to dynamically assemble your queries. Use normal python string templating to sub in table and column names, glue on where clauses and joins, all the good (and horrible to debug) stuff. But make sure you're aware that whatever values such code touches has to come from you, not your users[1]. Then you use SQLite's parameter substitution functionality to safely insert user-input values into your queries as values.
[1] If (as is the case for a lot of the code I write) your users are the people who have full access to databases anyway and the code is to simplify their work, then this consideration doesn't really apply; you probably are assembling queries on user-specified tables. But you should still use SQLite's parameter substitution to save yourself from the inevitable genuine value that eventually contains quotes or percent signs.
If you're quite certain that you need to specify column names dynamically, you should use a library that can do so safely (and complains about things that are wrong). SQLAlchemy is very good at that.
>>> import sqlalchemy
>>> from sqlalchemy import *
>>> metadata = MetaData()
>>> dynamic_column = "cow"
>>> foo_table = Table('foo', metadata,
... Column(dynamic_column, Integer))
>>>
foo_table now represents the table with the dynamic schema, but you can only use it in the context of an actual database connection (so that sqlalchemy knows the dialect, and what to do with the generated sql).
>>> metadata.bind = create_engine('sqlite:///:memory:', echo=True)
You can then issue the CREATE TABLE .... with echo=True, sqlalchemy will log the generated sql, but in general, sqlalchemy goes out of its way to keep the generated sql out of your hands (lest you consider using it for evil purposes).
>>> foo_table.create()
2011-06-28 21:54:54,040 INFO sqlalchemy.engine.base.Engine.0x...2f4c
CREATE TABLE foo (
cow INTEGER
)
2011-06-28 21:54:54,040 INFO sqlalchemy.engine.base.Engine.0x...2f4c ()
2011-06-28 21:54:54,041 INFO sqlalchemy.engine.base.Engine.0x...2f4c COMMIT
>>>
and yes, sqlalchemy will take care of any column names that need special handling, like when the column name is a sql reserved word
>>> dynamic_column = "order"
>>> metadata = MetaData()
>>> foo_table = Table('foo', metadata,
... Column(dynamic_column, Integer))
>>> metadata.bind = create_engine('sqlite:///:memory:', echo=True)
>>> foo_table.create()
2011-06-28 22:00:56,267 INFO sqlalchemy.engine.base.Engine.0x...aa8c
CREATE TABLE foo (
"order" INTEGER
)
2011-06-28 22:00:56,267 INFO sqlalchemy.engine.base.Engine.0x...aa8c ()
2011-06-28 22:00:56,268 INFO sqlalchemy.engine.base.Engine.0x...aa8c COMMIT
>>>
and can save you from possible badness:
>>> dynamic_column = "); drop table users; -- the evil bobby tables!"
>>> metadata = MetaData()
>>> foo_table = Table('foo', metadata,
... Column(dynamic_column, Integer))
>>> metadata.bind = create_engine('sqlite:///:memory:', echo=True)
>>> foo_table.create()
2011-06-28 22:04:22,051 INFO sqlalchemy.engine.base.Engine.0x...05ec
CREATE TABLE foo (
"); drop table users; -- the evil bobby tables!" INTEGER
)
2011-06-28 22:04:22,051 INFO sqlalchemy.engine.base.Engine.0x...05ec ()
2011-06-28 22:04:22,051 INFO sqlalchemy.engine.base.Engine.0x...05ec COMMIT
>>>
(apparently, some strange things are perfectly legal identifiers in sqlite)
The first thing to understand is that table/column names cannot be escaped in the same sense than you can escape strings stored as database values.
The reason is that you either have to:
accept/reject the potential table/column name, i.e. it is not guaranteed that a string is an acceptable column/table name, contrarily to a string to be stored in some database; or,
sanitize the string which will have the same effect as creating a digest: the function used is surjective, not bijective (once again, the inverse is true for a string that is to be stored in some database); so not only can't you be certain of going from the sanitized name back to the original name, but you are at risk of unintentionally trying to create two columns or tables with the same name.
Having understood that, the second thing to understand is that how you will end up "escaping" table/column names depends on your specific context, and so there is more than one way to do this, but whatever the way, you'll need to dig up to figure out exactly what is or is not an acceptable column/table name in sqlite.
To get you started, here is one condition:
Table names that begin with "sqlite_" are reserved for internal use. It is an error to attempt to create a table with a name that starts with "sqlite_".
Even better, using certain column names can have unintended side effects:
Every row of every SQLite table has a 64-bit signed integer key that
uniquely identifies the row within its table. This integer is usually
called the "rowid". The rowid value can be accessed using one of the
special case-independent names "rowid", "oid", or "rowid" in place
of a column name. If a table contains a user defined column named
"rowid", "oid" or "rowid", then that name always refers the
explicitly declared column and cannot be used to retrieve the integer
rowid value.
Both quoted texts are from http://www.sqlite.org/lang_createtable.html
From the sqlite faq, question 24 (the formulation of the question of course does not give a clue that the answer may be useful to your question):
SQL uses double-quotes around identifiers (column or table names) that contains special characters or which are keywords. So double-quotes are a way of escaping identifier names.
If the name itself contains double quotes, escape that double quote with another one.
Placeholders are only for values. Column and table names are structural, and are akin to variable names; you can't use placeholders to fill them in.
You have three options:
Appropriately escape/quote the column name everywhere you use it. This is fragile and dangerous.
Use an ORM like SQLAlchemy, which will take care of escaping/quoting for you.
Ideally, just don't have dynamic column names. Tables and columns are for structure; anything dynamic is data and should be in the table rather than part of it.
I made some research because I was unsatisfied with the current unsafe answers, and I would recommend using the internal printf function of sqlite to do that. It is made to escape any identifier (table name, column table...) and make it safe for concatenation.
In python, it should be something like that (I'm not a python user, so there may be mistakes, but the logic itself works):
table = "bar"
escaped_table = connection.execute("SELECT printf('%w', ?)", (table,)).fetchone()[0]
connection.execute("CREATE TABLE \""+escaped_table+"\" (bar TEXT)")
According to the documentation of %w:
This substitution works like %q except that it doubles all double-quote characters (") instead of single-quotes, making the result suitable for using with a double-quoted identifier name in an SQL statement.
The %w substitution is an SQLite enhancements, not found in most other printf() implementations.
Which means you can alternatively do the same with single quotes using %q:
table = "bar"
escaped_table = connection.execute("SELECT printf('%q', ?)", (table,)).fetchone()[0]
connection.execute("CREATE TABLE '"+escaped_table+"' (bar TEXT)")
If you find that you need a variable entity name (either relvar or field) then you probably are doing something wrong. an alternative pattern would be to use a property map, something like:
CREATE TABLE foo_properties(
id INTEGER NOT NULL,
name VARCHAR NOT NULL,
value VARCHAR,
PRIMARY KEY(id, name)
);
Then, you just specify the name dynamically when doing an insert instead of a column.
When I use the Execute Script operator, where there is one input arc and this input is of type ExampleSet and I run, for example, the one-line script return operator.getInput(ExampleSet.class), and then connect the output to an Extract Performance operator, which takes an ExampleSet as input, I get an error: Mandatory input missing at port Performance.example set.
My goal is to check a Petri-net for soundness via the Analyse soundness operator that comes with the RapidProm extension, and to take and change the first attribute on the first line to either 0 or 1 depending on whether this string matches "is sound", so I can then use Extract Performance and combine it with other performances using Average.
Is doing this with Execute Script the right way to do it, and if so, how should I fix this error?
Firstly: Don't bother about the error Mandatory input missing at port Performance.example set
It will be resolved when you run the model.
Secondly: It is indeed a bit ugly, the output of the operator that checks
the soundness of the model, since it is a very long string that looks like
Woflan diagnosis of net "d1cf46bd-15a9-4801-9f02-946a8f125eaf" - The net is sound End of Woflan diagnosis
You can indeed use the execute script to resolve this :)
See the script below!
The output is an example set that returns 1 if the model is sound, and 0 otherwise. Furthermore, I like to use some log operators to translate this to a nice table useful for documentation purposes.
ExampleSet input = operator.getInput(ExampleSet.class);
for (Example example : input) {
String uglyResult = example["att1"];
String soundResult = "The net is sound";
Boolean soundnessCheck = uglyResult.toLowerCase().contains(soundResult.toLowerCase());
if (soundnessCheck){
example["att1"] = "1"; //the net is sound :)
} else {
example["att1"] = "0"; //the net is not sound!
}
}
return input;
See also the attached example model I created.
RapidMiner Setup
I've run across some node.js code that gets a user-supplied string, calls JSON.stringify(str) and injects the value directly into an SQL statement.
e.g.
var x = JSON.stringify(UNSAFE_USER_STRING);
mysql_execute('UPDATE foo SET v = ' + x + ' WHERE id = 1');
Obviously this is an abuse of JSON.stringify, however this is not my code and the authors would like to see an attack vector before they patch it. Because UNSAFE_USER_STRING is a string, not an object and does escaping of the obvious " and \ it's not obvious if there is a serious problem
Is this code safe? And if not, could someone demonstrate what would be unsafe input?
Thanks!
If you are sure x is a string, then I'm 99% sure this makes it impossible to conduct an SQL injection attack. My confidence goes down to 90% when you are unsure of the type for x. That said, considering all of the following should not pose a vulnerability:
Null, NaN, Infinity, -Infinity all seem to come back as null which is safe.
Undefined comes back as the value undefined, not a string, so I'm not sure about that. I think it would just be considered invalid SQL rather than pose a vulnerability.
Date in node.js JSON.stringify(new Date()) returns '"2015-11-09T18:53:46.198Z"' which is exactly what you'd want.
Arrays and Objects should result in invalid SQL although a smart conversion could enable successful use of SQL arrays. That said, there might be some tricky way to fill the array with Objects that might cause a vulnerability, but I doubt it.
Hex seems to just convert it to an integer.
Buffers and Uint8Arrays seem to come back as objects. Again, there might be some way to populate the Object with something that would be a vulnerability, but I doubt it.
Even if characters like " are being escaped. Character(combinations) used for comments like -- or # could still cause the WHERE clause to be ignored.
As we all know, we will use the mysql_query api to send a query to the server, and the query are passed by a string as the parameter. And we will have to formulate the string outside the mysql_query called by some C functions like sprintf.For example,
sprintf(buffer, “insert into table(describe) values(‘%s’)”, strA);
mysql_query(..., buffer);
The ‘describe’ is a VARCHAR(150).
In some special cases, one of our functions will cat several C style string into a long one remaining all the ending ‘\0’ to form a binary, ie in C form catting “abc” and “efg” into “abc\0efg\0”, of course with the length given out to the caller(in this case, it is 8). However, the out binary can NEVER be used in the sprintf above as strA, as the C functions will truncate the string by meeting the first ‘\0’.
Is there anything special we can do to fulfill our needs? We want to insert a binary into a column defined as VARCHAR. We have tried to change all the ‘\0’ into ‘\0’ literally, which seems to work good but time and codes consuming. Is there any alternative easier method?
Thanks in advance.
you should use mysql_real_escape_string() to escape this string.
I have structure of Tcl_Interp for which I don't know what is holding. I tried to print a string value of interp.result but it's not returning anything. I am using this function:
void debug_state(char *state);
like this:
debug_state(Tcl_GetStringResult(g_game.tcl_interp));
but it isn't returning anything. Is there other way to see string value of tcl_interp other than char *Tcl_GetStringResult(interp)
You are not supposed to use the Tcl_Interp* as anything other than an opaque handle to an interpreter. Once upon a time you used interp->result to access the result but this has been deprecated for over a decade. As you have found, Tcl_GetStringResult and often better, Tcl_GetObjResult should be used. In general, in new code you should try to use the Tcl_Obj functions rather than the string functions as this can avoid conversions to and from string types when not necessary.
Your code should be ok, provided debug_state doesn't expect the result value to be valid after your function returns. I would say if you are seeing an empty string that this point then that is what is in your interpreter result. You could check that by setting it to something just before eg: Tcl_SetObjResult(interp, Tcl_NewStringObj("testing, testing...", -1));. If you then call Tcl_GetStringResult(interp) you should get a char * pointer to a copy of the above string.