Commit 43bd40e5 authored by Mike Frysinger's avatar Mike Frysinger Committed by Linus Torvalds
Browse files

binfmt_misc: touch up documentation a bit 



Line wrap the content to 80 cols, and add more details to various fields
to match the code.  Drop reference to a website that does not exist
anymore.

Signed-off-by: default avatarMike Frysinger <vapier@gentoo.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent bbaecc08

Documentation/binfmt_misc.txt

+28 −20
Original line number Original line Diff line number Diff line
@@ -15,39 +15,50 @@ First you must mount binfmt_misc: 
	mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc 

	mount binfmt_misc -t binfmt_misc /proc/sys/fs/binfmt_misc 





To actually register a new binary type, you have to set up a string looking like

To actually register a new binary type, you have to set up a string looking like

:name:type:offset:magic:mask:interpreter:flags (where you can choose the ':' upon

:name:type:offset:magic:mask:interpreter:flags (where you can choose the ':'

your needs) and echo it to /proc/sys/fs/binfmt_misc/register.

upon your needs) and echo it to /proc/sys/fs/binfmt_misc/register.



Here is what the fields mean:

Here is what the fields mean:

 - 'name' is an identifier string. A new /proc file will be created with this

 - 'name' is an identifier string. A new /proc file will be created with this

   name below /proc/sys/fs/binfmt_misc

   name below /proc/sys/fs/binfmt_misc; cannot contain slashes '/' for obvious

   reasons.

 - 'type' is the type of recognition. Give 'M' for magic and 'E' for extension.

 - 'type' is the type of recognition. Give 'M' for magic and 'E' for extension.

 - 'offset' is the offset of the magic/mask in the file, counted in bytes. This

 - 'offset' is the offset of the magic/mask in the file, counted in bytes. This

   defaults to 0 if you omit it (i.e. you write ':name:type::magic...')

   defaults to 0 if you omit it (i.e. you write ':name:type::magic...'). Ignored

   when using filename extension matching.

 - 'magic' is the byte sequence binfmt_misc is matching for. The magic string

 - 'magic' is the byte sequence binfmt_misc is matching for. The magic string

   may contain hex-encoded characters like \x0a or \xA4. In a shell environment

   may contain hex-encoded characters like \x0a or \xA4. Note that you must

   you will have to write \\x0a to prevent the shell from eating your \.

   escape any NUL bytes; parsing halts at the first one. In a shell environment

   you might have to write \\x0a to prevent the shell from eating your \.

   If you chose filename extension matching, this is the extension to be

   If you chose filename extension matching, this is the extension to be

   recognised (without the '.', the \x0a specials are not allowed). Extension

   recognised (without the '.', the \x0a specials are not allowed). Extension

   matching is case sensitive!

   matching is case sensitive, and slashes '/' are not allowed!

 - 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some

 - 'mask' is an (optional, defaults to all 0xff) mask. You can mask out some

   bits from matching by supplying a string like magic and as long as magic.

   bits from matching by supplying a string like magic and as long as magic.

   The mask is anded with the byte sequence of the file.

   The mask is anded with the byte sequence of the file. Note that you must

   escape any NUL bytes; parsing halts at the first one. Ignored when using

   filename extension matching.

 - 'interpreter' is the program that should be invoked with the binary as first

 - 'interpreter' is the program that should be invoked with the binary as first

   argument (specify the full path)

   argument (specify the full path)

 - 'flags' is an optional field that controls several aspects of the invocation

 - 'flags' is an optional field that controls several aspects of the invocation

   of the interpreter. It is a string of capital letters, each controls a certain

   of the interpreter. It is a string of capital letters, each controls a

   aspect. The following flags are supported -

   certain aspect. The following flags are supported -

      'P' - preserve-argv[0].  Legacy behavior of binfmt_misc is to overwrite the

      'P' - preserve-argv[0]. Legacy behavior of binfmt_misc is to overwrite

            original argv[0] with the full path to the binary.  When this flag is

            the original argv[0] with the full path to the binary. When this

            included, binfmt_misc will add an argument to the argument vector for

            flag is included, binfmt_misc will add an argument to the argument

            this purpose, thus preserving the original argv[0].

            vector for this purpose, thus preserving the original argv[0].

            e.g. If your interp is set to /bin/foo and you run `blah` (which is

            in /usr/local/bin), then the kernel will execute /bin/foo with

            argv[] set to ["/bin/foo", "/usr/local/bin/blah", "blah"].  The

            interp has to be aware of this so it can execute /usr/local/bin/blah

            with argv[] set to ["blah"].

      'O' - open-binary. Legacy behavior of binfmt_misc is to pass the full path

      'O' - open-binary. Legacy behavior of binfmt_misc is to pass the full path

            of the binary to the interpreter as an argument. When this flag is

            of the binary to the interpreter as an argument. When this flag is

            included, binfmt_misc will open the file for reading and pass its

            included, binfmt_misc will open the file for reading and pass its

            descriptor as an argument, instead of the full path, thus allowing

            descriptor as an argument, instead of the full path, thus allowing

            the interpreter to execute non-readable binaries. This feature should

            the interpreter to execute non-readable binaries. This feature

            be used with care - the interpreter has to be trusted not to emit

            should be used with care - the interpreter has to be trusted not to

            the contents of the non-readable binary.

            emit the contents of the non-readable binary.

      'C' - credentials. Currently, the behavior of binfmt_misc is to calculate

      'C' - credentials. Currently, the behavior of binfmt_misc is to calculate

            the credentials and security token of the new process according to

            the credentials and security token of the new process according to

            the interpreter. When this flag is included, these attributes are

            the interpreter. When this flag is included, these attributes are
@@ -110,7 +121,4 @@ passes it the full filename (or the file descriptor) to use. Using $PATH can 
cause unexpected behaviour and can be a security hazard.

cause unexpected behaviour and can be a security hazard.









There is a web page about binfmt_misc at

http://www.tat.physik.uni-tuebingen.de



Richard Günther <rguenth@tat.physik.uni-tuebingen.de>
 
Richard Günther <rguenth@tat.physik.uni-tuebingen.de>