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Cygwin: Fix and streamline AT_EMPTY_PATH handling 

The GLIBC extension AT_EMPTY_PATH allows the functions fchownat
and fstatat to operate on dirfd alone, if the given pathname is an
empty string.  This also allows to operate on any file type, not
only directories.

Commit fa84aa4dd2 broke this.  It only allows dirfd to be a
directory in calls to these two functions.

Fix that by handling AT_EMPTY_PATH right in gen_full_path_at.
A valid dirfd and an empty pathname is now a valid combination
and, noticably, this returns a valid path in path_ret.  That
in turn allows to remove the additional path generation code
from the callers.

Fixes: fa84aa4dd2 ("Cygwin: fix errno values set by readlinkat")
Reported-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Tested-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
This commit is contained in:
Corinna Vinschen 2023-07-12 13:47:49 +02:00
parent 0051091999
commit f48ce81122
1 changed files with 11 additions and 36 deletions
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47
winsup/cygwin/syscalls.cc
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@ -4441,7 +4441,7 @@ gen_full_path_at (char *path_ret, int dirfd, const char *pathname,
cygheap_fdget cfd (dirfd); cygheap_fdget cfd (dirfd);
if (cfd < 0) if (cfd < 0)
return -1; return -1;
if (!cfd->pc.isdir ()) if (!cfd->pc.isdir () && !(flags & AT_EMPTY_PATH))
{ {
set_errno (ENOTDIR); set_errno (ENOTDIR);
return -1; return -1;
@ -4452,6 +4452,8 @@ gen_full_path_at (char *path_ret, int dirfd, const char *pathname,
{ {
if (!*pathname) if (!*pathname)
{ {
if (flags & AT_EMPTY_PATH)
return 0;
set_errno (ENOENT); set_errno (ENOENT);
return -1; return -1;
} }
@ -4573,29 +4575,14 @@ fchownat (int dirfd, const char *pathname, uid_t uid, gid_t gid, int flags)
__leave; __leave;
} }
char *path = tp.c_get (); char *path = tp.c_get ();
int res = gen_full_path_at (path, dirfd, pathname); int res = gen_full_path_at (path, dirfd, pathname, flags);
if (res) if (res)
__leave;
if (!*pathname) /* Implies AT_EMPTY_PATH */
{ {
if (!(errno == ENOENT && (flags & AT_EMPTY_PATH))) /* If dirfd refers to a symlink (which was necessarily opened with
__leave; O_PATH | O_NOFOLLOW), we must operate directly on that symlink. */
/* pathname is an empty string. Operate on dirfd. */ flags = AT_SYMLINK_NOFOLLOW;
if (dirfd == AT_FDCWD)
{
cwdstuff::acquire_read ();
strcpy (path, cygheap->cwd.get_posix ());
cwdstuff::release_read ();
}
else
{
cygheap_fdget cfd (dirfd);
if (cfd < 0)
__leave;
strcpy (path, cfd->get_name ());
/* If dirfd refers to a symlink (which was necessarily
opened with O_PATH | O_NOFOLLOW), we must operate
directly on that symlink.. */
flags = AT_SYMLINK_NOFOLLOW;
}
} }
return chown_worker (path, (flags & AT_SYMLINK_NOFOLLOW) return chown_worker (path, (flags & AT_SYMLINK_NOFOLLOW)
? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW, uid, gid); ? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW, uid, gid);
@ -4618,21 +4605,9 @@ fstatat (int dirfd, const char *__restrict pathname, struct stat *__restrict st,
__leave; __leave;
} }
char *path = tp.c_get (); char *path = tp.c_get ();
int res = gen_full_path_at (path, dirfd, pathname); int res = gen_full_path_at (path, dirfd, pathname, flags);
if (res) if (res)
{ __leave;
if (!(errno == ENOENT && (flags & AT_EMPTY_PATH)))
__leave;
/* pathname is an empty string. Operate on dirfd. */
if (dirfd == AT_FDCWD)
{
cwdstuff::acquire_read ();
strcpy (path, cygheap->cwd.get_posix ());
cwdstuff::release_read ();
}
else
return fstat (dirfd, st);
}
path_conv pc (path, ((flags & AT_SYMLINK_NOFOLLOW) path_conv pc (path, ((flags & AT_SYMLINK_NOFOLLOW)
? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW) ? PC_SYM_NOFOLLOW : PC_SYM_FOLLOW)
| PC_POSIX | PC_KEEP_HANDLE, stat_suffixes); | PC_POSIX | PC_KEEP_HANDLE, stat_suffixes);