vfs: add faccessat2 syscall
POSIX defines faccessat() as having a fourth "flags" argument, while the
linux syscall doesn't have it. Glibc tries to emulate AT_EACCESS and
AT_SYMLINK_NOFOLLOW, but AT_EACCESS emulation is broken.
Add a new faccessat(2) syscall with the added flags argument and implement
both flags.
The value of AT_EACCESS is defined in glibc headers to be the same as
AT_REMOVEDIR. Use this value for the kernel interface as well, together
with the explanatory comment.
Also add AT_EMPTY_PATH support, which is not documented by POSIX, but can
be useful and is trivial to implement.
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
diff --git a/fs/open.c b/fs/open.c
index 0ea3cd1..e62b1db 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -394,20 +394,30 @@ static const struct cred *access_override_creds(void)
return old_cred;
}
-long do_faccessat(int dfd, const char __user *filename, int mode)
+long do_faccessat(int dfd, const char __user *filename, int mode, int flags)
{
struct path path;
struct inode *inode;
int res;
unsigned int lookup_flags = LOOKUP_FOLLOW;
- const struct cred *old_cred;
+ const struct cred *old_cred = NULL;
if (mode & ~S_IRWXO) /* where's F_OK, X_OK, W_OK, R_OK? */
return -EINVAL;
- old_cred = access_override_creds();
- if (!old_cred)
- return -ENOMEM;
+ if (flags & ~(AT_EACCESS | AT_SYMLINK_NOFOLLOW | AT_EMPTY_PATH))
+ return -EINVAL;
+
+ if (flags & AT_SYMLINK_NOFOLLOW)
+ lookup_flags &= ~LOOKUP_FOLLOW;
+ if (flags & AT_EMPTY_PATH)
+ lookup_flags |= LOOKUP_EMPTY;
+
+ if (!(flags & AT_EACCESS)) {
+ old_cred = access_override_creds();
+ if (!old_cred)
+ return -ENOMEM;
+ }
retry:
res = user_path_at(dfd, filename, lookup_flags, &path);
@@ -450,18 +460,26 @@ long do_faccessat(int dfd, const char __user *filename, int mode)
goto retry;
}
out:
- revert_creds(old_cred);
+ if (old_cred)
+ revert_creds(old_cred);
+
return res;
}
SYSCALL_DEFINE3(faccessat, int, dfd, const char __user *, filename, int, mode)
{
- return do_faccessat(dfd, filename, mode);
+ return do_faccessat(dfd, filename, mode, 0);
+}
+
+SYSCALL_DEFINE4(faccessat2, int, dfd, const char __user *, filename, int, mode,
+ int, flags)
+{
+ return do_faccessat(dfd, filename, mode, flags);
}
SYSCALL_DEFINE2(access, const char __user *, filename, int, mode)
{
- return do_faccessat(AT_FDCWD, filename, mode);
+ return do_faccessat(AT_FDCWD, filename, mode, 0);
}
int ksys_chdir(const char __user *filename)