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Cygwin: fix errno values set by readlinkat 

readlinkat(fd, "", ...) is supposed to return ENOENT per POSIX,
but Cygwin returns EBADF.

At the same time, we have to maintain the special feature of
glibc that readlinkat(fd, "", ...) operates on fd, if fd is pointing
at a symlink opened with O_PATH|O_NOFOLLOW.

And, while fixing that, readlinkat(fd, path, ...) *still* has to set errno
to EBADF, if fd is an invalid descriptor *and* path is a relative path.

This required to change the evaluation order in the helper function
gen_full_path_at.

Last but not least, in case of the aforementioned glibc-like special
handling for symlink descriptors, we have to make sure that errors from
gen_full_path_at are not spilled into that special handling.

Fixes: 6cc05784e1 ("Cygwin: readlinkat: allow pathname to be empty")
Reported-by: Bruno Haible <bruno@clisp.org>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2023-04-18 13:52:50 +02:00
parent f87469dd5b
commit 4b8222983f
2 changed files with 25 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
winsup/cygwin/release/3.4.7
View File

@ -18,3 +18,6 @@ Bug Fixes
- Fix return value of ilogbl(NaN).
Addresses: https://cygwin.com/pipermail/cygwin/2023-April/253511.html
- Fix error handling in readlinkat.
Addresses: https://cygwin.com/pipermail/cygwin/2023-April/253510.html

42
winsup/cygwin/syscalls.cc
View File

@ -4415,19 +4415,6 @@ gen_full_path_at (char *path_ret, int dirfd, const char *pathname,
set_errno (EFAULT);
return -1;
}
if (pathname)
{
if (!*pathname)
{
set_errno (ENOENT);
return -1;
}
if (strlen (pathname) >= PATH_MAX)
{
set_errno (ENAMETOOLONG);
return -1;
}
}
if (pathname && isabspath_strict (pathname))
stpcpy (path_ret, pathname);
else
@ -4459,6 +4446,16 @@ gen_full_path_at (char *path_ret, int dirfd, const char *pathname,
}
if (pathname)
{
if (!*pathname)
{
set_errno (ENOENT);
return -1;
}
if (strlen (pathname) >= PATH_MAX)
{
set_errno (ENAMETOOLONG);
return -1;
}
if (p[-1] != '/')
*p++ = '/';
stpcpy (p, pathname);
@ -4803,21 +4800,26 @@ readlinkat (int dirfd, const char *__restrict pathname, char *__restrict buf,
__try
{
char *path = tp.c_get ();
int save_errno = errno;
int res = gen_full_path_at (path, dirfd, pathname);
if (res)
{
if (errno != ENOENT)
if (errno != ENOENT && errno != ENOTDIR)
__leave;
/* pathname is an empty string. This is OK if dirfd refers
to a symlink that was opened with O_PATH | O_NOFOLLOW.
In this case, readlinkat operates on the symlink. */
In this case, readlinkat operates on the symlink.
Don't propagate errors from gen_full_path_at after this point. */
errno = save_errno;
cygheap_fdget cfd (dirfd);
if (cfd < 0)
__leave;
if (!(cfd->issymlink ()
if (cfd < 0
|| (!(cfd->issymlink ()
&& cfd->get_flags () & O_PATH
&& cfd->get_flags () & O_NOFOLLOW))
__leave;
&& cfd->get_flags () & O_NOFOLLOW)))
{
set_errno (ENOENT);
__leave;
}
strcpy (path, cfd->get_name ());
}
return readlink (path, buf, bufsize);