Re: Grant Update (Possible bug)?

From: Ilir Gashi <I(dot)Gashi(at)city(dot)ac(dot)uk>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: pgsql-bugs(at)postgresql(dot)org
Subject: Re: Grant Update (Possible bug)?
Date: 2004-07-02 14:34:20
Message-ID: E1BgP7M-0005r0-00@ms2.city.ac.uk
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On Jul 2 2004, Tom Lane wrote:

> Ilir Gashi <I(dot)Gashi(at)city(dot)ac(dot)uk> writes:
> > This is a another bug reported for the Firebird 1.0 server. I
> > subsequently ran it in PostgreSQL 7.2, Oracle 8.0.5 anf MSSQL 7.
>
> > Reproducible script:
>
> > Connect as pgsql:
>
> > CREATE TABLE TEST(ID INTEGER,NAME VARCHAR(50));
>
> > INSERT INTO TEST (ID) VALUES (1);
>
> > GRANT UPDATE ON TEST TO TESTUSER;
>
> > Connect as TestUser;
>
> > UPDATE TEST SET NAME='TEST' WHERE ID=1;
>
> > ERROR: test: Permission denied.
>
> > UPDATE TEST SET NAME='TEST';
>
> > Executes successfully.
>
> This is not a bug. That UPDATE requires SELECT permission because it
> makes use of the ID field in the where clause. If you grant someone
> UPDATE but not SELECT, presumably you want them to be able to insert
> data but not learn anything about what is in the table. If we allowed
> such commands then something like
> UPDATE TEST SET NAME = NAME WHERE ID = 1
> could be used to determine whether the table contains a row with ID=1
> (by inspecting the reported row count). So it would be a security flaw.
>
> The SQL specification also requires this behavior. In SQL92 the Access
> Rules for <column reference> say
>
> 1) The applicable privileges shall include SELECT for T if CR is
> contained in any of:
>
> a) a <search condition> immediately contained in a <delete
> statement: searched> or an <update statement: searched>; or
>
> b) a <value expression> immediately contained in an <update
> source>.
>
> > So the user can update the whole table but not specific columns. Is
> > this a bug or as specified (I read briefly the Reference Guide and I
> > didn't see this highlited anywhere, but I may have missed it.).
> > Firebird and MSSQL have the same behaviour as PostgreSQL (Firebird have
> > acknowledged this as a bug, I haven't checked on MSSQL website yet.)
>
> It's not a bug. Please withdraw the complaint against Firebird.
>
> > In Oracle 8.0.5 both updates execute sucessfully.
>
> Oracle is a very poor reference for SQL-spec-compliant behavior :-(
>
> regards, tom lane

Thanks for the quick reply. I also suspected that it was not a bug, but was
confused by The Firebird bug-tracker at SourceForge who had marked it as an
'Initial bug', and became even more confused from the behaviour of Oracle.
Thanks for the clarification.

Best regards,

Ilir

____________________________________________

Ilir Gashi
PhD Student
Centre for Software Reliability
City University
Northampton Square, London EC1V 0HB
email: i(dot)gashi(at)city(dot)ac(dot)uk
website: http://www.csr.city.ac.uk/csr_city/staff/gashi/
____________________________________________

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