setuid bit

• How do programs get run?

  1. Process A running as user U wants to run program B

  2. A does fork, which clones process A into a parent and a child

  3. The child scoops out its brain, replaces with B

• The child is still running as user U

• Exception: if file B has the setuid bit set

  • Then in step 3, the child is granted a new UID

  • It gets the UID of the owner of file B

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Copyright © 2005 M. J. Dominus