RE: [PATCH] vfs: add fchmodat2 syscall
From: David Laight <hidden>
Date: 2020-09-10 19:47:23
Also in:
linux-fsdevel, lkml
From: Rich Felker
Sent: 10 September 2020 15:24
...
quoted hunk ↗ jump to hunk
index 9af548fb841b..570a21f4d81e 100644--- a/fs/open.c +++ b/fs/open.c@@ -610,15 +610,30 @@ SYSCALL_DEFINE2(fchmod, unsigned int, fd, umode_t, mode) return err; } -static int do_fchmodat(int dfd, const char __user *filename, umode_t mode) +static int do_fchmodat(int dfd, const char __user *filename, umode_t mode, int flags) { struct path path; int error; unsigned int lookup_flags = LOOKUP_FOLLOW; + + if (flags & AT_SYMLINK_NOFOLLOW) + lookup_flags &= ~LOOKUP_FOLLOW; + if (flags & ~AT_SYMLINK_NOFOLLOW) + return -EINVAL;
I think I'd swap over those two tests. So unsupported flags are clearly errored.
retry:
error = user_path_at(dfd, filename, lookup_flags, &path);
if (!error) {
- error = chmod_common(&path, mode);
+ /* Block chmod from getting to fs layer. Ideally the
+ * fs would either allow it or fail with EOPNOTSUPP,
+ * but some are buggy and return an error but change
+ * the mode, which is non-conforming and wrong.
+ * Userspace emulation of AT_SYMLINK_NOFOLLOW in
+ * glibc and musl blocked it too, for same reason. */
+ if (S_ISLNK(path.dentry->d_inode->i_mode)
+ && (flags & AT_SYMLINK_NOFOLLOW))
+ error = -EOPNOTSUPP;Again swap the order of the tests. I think it reads better as: if ((flags & AT_SYMLINK_NOFOLLOW) && S_ISLNK(path.dentry->d_inode->i_mode)) error = -EOPNOTSUPP; As well as saving a few clock cycles.
+ else
+ error = chmod_common(&path, mode);
path_put(&path);
if (retry_estale(error, lookup_flags)) {
lookup_flags |= LOOKUP_REVAL;... David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)