getcwd01,readlinkat02 fails in Alpine 3.18 container

[richiejp]

The test passes NULL as the buffer to getcwd. This causes musl to allocate a buffer and ignore the length argument. The test then passes unexpectedly.

glibc should do the same, but it possibly checks the length argument or passes it to the syscall.

[metan-ucw]

Looks like glibc uses the size argument to allocate the buffer unless it's 0. So I suppose that musl ignores the size completely and allocates the buffer so that it fits the path.

[richiejp]

readlinkat02 fails for a similar reason. Except that this time musl checks the buffer size instead and uses a stack buffer.

[richiejp]

uclibc-ng does the same as glibc

[coolgw]

uclibc-ng:
https://github.com/wbx-github/uclibc-ng/blob/cdb07d2cd52af39feb425e6d36c02b30916b9f0a/libc/sysdeps/linux/common/getcwd.c#L37

musl:
https://github.com/bminor/musl/blob/79bdacff83a6bd5b70ff5ae5eb8b6de82c2f7c30/src/unistd/getcwd.c#L10

Both malloc buffer if buf==NULL.
https://patchwork.ozlabs.org/project/ltp/patch/20230928010808.15862-1-wegao@suse.com/

[coolgw]

uclibc-ng:
https://github.com/wbx-github/uclibc-ng/blob/cdb07d2cd52af39feb425e6d36c02b30916b9f0a/libc/sysdeps/linux/common/getcwd.c#L37

musl:
https://github.com/bminor/musl/blob/79bdacff83a6bd5b70ff5ae5eb8b6de82c2f7c30/src/unistd/getcwd.c#L10

Both malloc buffer if buf==NULL.
https://patchwork.ozlabs.org/project/ltp/patch/20230928010808.15862-1-wegao@suse.com/

[pevik]

Both malloc buffer if buf==NULL. https://patchwork.ozlabs.org/project/ltp/patch/20230928010808.15862-1-wegao@suse.com/

@coolgw malloc() is not relevant to the problem, MUSL fails due the reason described by Richie original report #1084 (comment): musl on null buffer allocates a buffer but ignore the length argument. Unlike glibc, uclibc{,-ng}. IMHO also bionic is compatible with glibc, uclibc{,-ng}(https://android.googlesource.com/platform/bionic.git/+/refs/heads/main/libc/bionic/getcwd.cpp), because it uses size on null buffer.