musl as a whole is licensed under the following standard MIT license:

Copyright © 2005-2012 Rich Felker

Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


Portions of this software are contributed or derived from software
authored by third parties. Complete details on the copyright status of
all code included in musl follows below:


The TRE regular expression implementation (src/regex/reg* and
src/regex/tre*) is Copyright © 2001-2008 Ville Laurikari and licensed
under a 2-clause BSD license (license text in the source files). The
included version has been heavily modified by Rich Felker in 2012, in
the interests of size, simplicity, and namespace cleanliness.

Most of the math library code (src/math/* and src/complex/*) is
Copyright © 1993,2004 Sun Microsystems or
Copyright © 2003-2011 David Schultz or
Copyright © 2003-2009 Steven G. Kargl or
Copyright © 2003-2009 Bruce D. Evans or
Copyright © 2008 Stephen L. Moshier
and labelled as such. All have been licensed under extremely
permissive terms. See the comments in the individual files for
details.

The implementation of DES for crypt (src/misc/crypt.c) is Copyright ©
1994 David Burren. It is licensed under a BSD license.

The smoothsort implementation (src/stdlib/qsort.c) is Copyright © 2011
Valentin Ochs and is licensed under an MIT-style license.

The BSD PRNG implementation (src/prng/random.c) and XSI search API
(src/search/*.c) functions are Copyright © 2011 Szabolcs Nagy and
licensed under following terms: "Permission to use, copy, modify,
and/or distribute this code for any purpose with or without fee is
hereby granted. There is no warranty."

The x86_64 port was written by Nicholas J. Kain. Several files (crt)
were released into the public domain; others are licensed under the
standard MIT license terms at the top of this file. See individual
files for their copyright status.

All files which have no copyright comments are original works
Copyright © 2005-2012 Rich Felker, the main author of this library.
The decision to exclude such comments is intentional, as it should be
possible to carry around the complete source code on tiny storage
media. All public header files (include/*) should be treated as Public
Domain as they intentionally contain no content which can be covered
by copyright. Some source modules may fall in this category as well.
If you believe that a file is so trivial that it should be in the
Public Domain, please contact me and, if I agree, I will explicitly
release it from copyright.

The following files are trivial, in my opinion not copyrightable in
the first place, and hereby explicitly released to the Public Domain:

All public headers: include/*
Startup files: crt/*