The switch to vfs_truncate in nfsd_setattr dropped the owner override
used for NFS permissions. Add a copy of vfs_truncate with it restored
to the nfsd code for now as it's very late in the cycle, but there
should be a way to consolidate it back in the future.
Fixes: 41f53350 ("nfsd: special case truncates some more")
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reported-by: Chuck Lever <chucklever@xxxxxxxxx>
---
fs/nfsd/vfs.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 80 insertions(+), 1 deletion(-)
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index a974368026a1..fd4a32e0b0b4 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -332,6 +332,85 @@ nfsd_sanitize_attrs(struct inode *inode, struct iattr *iap)
}
}
+/* copy of vfs_truncate with NFS owner override hacked in, sigh.. */
+static long nfsd_truncate(const struct path *path, loff_t length)
+{
+ struct inode *inode;
+ struct dentry *upperdentry;
+ long error;
+
+ inode = path->dentry->d_inode;
+
+ /* For directories it's -EISDIR, for other non-regulars - -EINVAL */
+ if (S_ISDIR(inode->i_mode))
+ return -EISDIR;
+ if (!S_ISREG(inode->i_mode))
+ return -EINVAL;
+
+ error = mnt_want_write(path->mnt);
+ if (error)
+ goto out;
+
+ /*
+ * The file owner always gets access permission for accesses that
+ * would normally be checked at open time. This is to make
+ * file access work even when the client has done a fchmod(fd, 0).
+ *
+ * However, `cp foo bar' should fail nevertheless when bar is
+ * readonly. A sensible way to do this might be to reject all
+ * attempts to truncate a read-only file, because a creat() call
+ * always implies file truncation.
+ * ... but this isn't really fair. A process may reasonably call
+ * ftruncate on an open file descriptor on a file with perm 000.
+ * We must trust the client to do permission checking - using "ACCESS"
+ * with NFSv3.
+ */
+ if (!uid_eq(inode->i_uid, current_fsuid())) {
+ error = inode_permission(inode, MAY_WRITE);
+ if (error)
+ goto mnt_drop_write_and_out;
+ }
+
+ error = -EPERM;
+ if (IS_APPEND(inode))
+ goto mnt_drop_write_and_out;
+
+ /*
+ * If this is an overlayfs then do as if opening the file so we get
+ * write access on the upper inode, not on the overlay inode. For
+ * non-overlay filesystems d_real() is an identity function.
+ */
+ upperdentry = d_real(path->dentry, NULL, O_WRONLY);
+ error = PTR_ERR(upperdentry);
+ if (IS_ERR(upperdentry))
+ goto mnt_drop_write_and_out;
+
+ error = get_write_access(upperdentry->d_inode);
+ if (error)
+ goto mnt_drop_write_and_out;
+
+ /*
+ * Make sure that there are no leases. get_write_access() protects
+ * against the truncate racing with a lease-granting setlease().
+ */
+ error = break_lease(inode, O_WRONLY);
+ if (error)
+ goto put_write_and_out;
+
+ error = locks_verify_truncate(inode, NULL, length);
+ if (!error)
+ error = security_path_truncate(path);
+ if (!error)
+ error = do_truncate(path->dentry, length, 0, NULL);
+
+put_write_and_out:
+ put_write_access(upperdentry->d_inode);
+mnt_drop_write_and_out:
+ mnt_drop_write(path->mnt);
+out:
+ return error;
+}
+
/*
* Set various file attributes. After this call fhp needs an fh_put.
*/
@@ -398,7 +477,7 @@ nfsd_setattr(struct svc_rqst *rqstp, struct svc_fh *fhp, struct iattr *iap,
((iap->ia_valid & ~(ATTR_SIZE | ATTR_MTIME)) == 0))
implicit_mtime = true;
- host_err = vfs_truncate(&path, iap->ia_size);
+ host_err = nfsd_truncate(&path, iap->ia_size);
if (host_err)
goto out_host_err;
--
2.11.0
--
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