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Oracle Tips by Burleson

Chapter 4 General Oracle Security

Each file in UNIX can be subject to three operations - reading, writing, and executing.  Every file has an owner. The permissions are defined on three sets of users - the owner of the file, the other members belonging to the group to which the file belongs, and finally, the rest of the users of that server. The permissions of a file are represented in UNIX via a set of letters. If the following commands are given

ls –l

The output will be something like this

-rwxr-xr--   1 oracle   dba        24608 Mar  4 03:06 osh

The first set of columns containing the letters r, x, and w - denotes the permissions of the file named osh. Let's dissect the permissions string to decode what it means.

The letters mean the permission types

  • r – read

  • w – write

  • x – execute

The first character denotes the type of the file. In this case this is a "-", indicating the fact that the file is a regular file. If this were a directory, this column would have shown the letter "d".

The next three characters show the permissions set for the owner of the file. The permissions are set in the format "rwx". If a particular permission is not available to that grantee, then it is denoted by a hyphen, "-". In this case, the letters are "rwx", which means that the

owner of the file, the user oracle, has the permission to read, write, and execute it.

The next three characters show the permissions given to the group. In this case, they are "r-x", and it indicates that the members of the group DBA (which is the group of the file) can read and execute the file but cannot write to it.

The last three characters show the permissions given to the rest of the users (sometimes called world permissions). In this example, it shows "r--", which means the users have only read permission on the file, not write and execute.

Another special type of permission exists, called the Set User ID Bit (SUID). Let's see how this works. Sometimes the owner of a file needs to operate on other files owned by it, or to modify processes it started. This owner may want to allow other users to perform the same tasks, but not give them special permission for all of these files and processes. Instead, the owner may set a special flag to indicate that the execution of this file by another user should be as if he or she is executing it.

An example is the executable file oracle, which is executed on behalf of the user who is connected to the database. This special flag is called a Set User ID Bit. If this is set, the permissions look like this.

-rwsr-s--x  1 oracle  dba  82292320 Mar 17 16:12 oracle

Note the letter "s" in the third place on the permissions for both the user and the group, where the letter "x"

Should have been. For the user permission, this simply indicates that the user executing the file will execute it as per the permissions of the owner of the file, oracle. Similarly, for group permission, the group owner's permissions are set at runtime.

This SUID permission is extremely powerful and should not be granted lightly, in fact, it should be avoided if possible. The Oracle installation itself puts SUID on some files in the bin directory under Oracle Home. Find these files by running the following command

ls – l|grep rws

Examine these files and determine if the SIOD is necessary as per the following chart. All these files are in the $ORACLE_HOME/bin directory.


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