From: Ralph Boehme <slow@samba.org>
Date: Thu, 8 Jun 2017 17:18:36 +0000 (+0200)
Subject: vfs_gpfs: handle EACCES when fetching DOS attributes from xattr
X-Git-Tag: samba-4.5.13~18
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad113e076b2a4875cbf056903a741ee913fd1688;p=thirdparty%2Fsamba.git

vfs_gpfs: handle EACCES when fetching DOS attributes from xattr

When trying to fetch the DOS attributes via gpfswrap_get_winattrs_path()
if the filesystem doesn't grant READ_ATTR to the file the function fails
with EACCESS.

But according to MS-FSA 2.1.5.1.2.1 "Algorithm to Check Access to an
Existing File" FILE_LIST_DIRECTORY on a directory implies
FILE_READ_ATTRIBUTES for directory entries.

So if the user can open the parent directory for reading this implies
FILE_LIST_DIRECTORY and we can safely call gpfswrap_get_winattrs_path()
with DAC_OVERRIDE_CAPABILITY.

Bug: https://bugzilla.samba.org/show_bug.cgi?id=12944

Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>

Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Wed Aug  9 01:21:14 CEST 2017 on sn-devel-144

(cherry picked from commit 62d73f5b936550d623ef4f31c7438ac3c90105b9)
---

diff --git a/source3/modules/vfs_gpfs.c b/source3/modules/vfs_gpfs.c
index f096dd54abf..78ebd54e494 100644
--- a/source3/modules/vfs_gpfs.c
+++ b/source3/modules/vfs_gpfs.c
@@ -1520,6 +1520,47 @@ static unsigned int vfs_gpfs_dosmode_to_winattrs(uint32_t dosmode)
 	return winattrs;
 }
 
+static int get_dos_attr_with_capability(struct smb_filename *smb_fname,
+					struct gpfs_winattr *attr)
+{
+	int saved_errno = 0;
+	int ret;
+
+	/*
+	 * According to MS-FSA 2.1.5.1.2.1 "Algorithm to Check Access to an
+	 * Existing File" FILE_LIST_DIRECTORY on a directory implies
+	 * FILE_READ_ATTRIBUTES for directory entries. Being able to stat() a
+	 * file implies FILE_LIST_DIRECTORY for the directory containing the
+	 * file.
+	 */
+
+	if (!VALID_STAT(smb_fname->st)) {
+		/*
+		 * Safety net: dos_mode() already checks this, but as we set
+		 * DAC_OVERRIDE_CAPABILITY based on this, add an additional
+		 * layer of defense.
+		 */
+		DBG_ERR("Rejecting DAC override, invalid stat [%s]\n",
+			smb_fname_str_dbg(smb_fname));
+		errno = EACCES;
+		return -1;
+	}
+
+	set_effective_capability(DAC_OVERRIDE_CAPABILITY);
+
+	ret = gpfswrap_get_winattrs_path(smb_fname->base_name, attr);
+	if (ret == -1) {
+		saved_errno = errno;
+	}
+
+	drop_effective_capability(DAC_OVERRIDE_CAPABILITY);
+
+	if (saved_errno != 0) {
+		errno = saved_errno;
+	}
+	return ret;
+}
+
 static NTSTATUS vfs_gpfs_get_dos_attributes(struct vfs_handle_struct *handle,
 					    struct smb_filename *smb_fname,
 					    uint32_t *dosmode)
@@ -1542,7 +1583,9 @@ static NTSTATUS vfs_gpfs_get_dos_attributes(struct vfs_handle_struct *handle,
 		return SMB_VFS_NEXT_GET_DOS_ATTRIBUTES(handle, smb_fname,
 						       dosmode);
 	}
-
+	if (ret == -1 && errno == EACCES) {
+		ret = get_dos_attr_with_capability(smb_fname, &attrs);
+	}
 	if (ret == -1) {
 		DBG_WARNING("Getting winattrs failed for %s: %s\n",
 			    smb_fname->base_name, strerror(errno));
@@ -1575,6 +1618,30 @@ static NTSTATUS vfs_gpfs_fget_dos_attributes(struct vfs_handle_struct *handle,
 		return SMB_VFS_NEXT_FGET_DOS_ATTRIBUTES(handle, fsp, dosmode);
 	}
 
+	if (ret == -1 && errno == EACCES) {
+		int saved_errno = 0;
+
+		/*
+		 * According to MS-FSA 2.1.5.1.2.1 "Algorithm to Check Access to
+		 * an Existing File" FILE_LIST_DIRECTORY on a directory implies
+		 * FILE_READ_ATTRIBUTES for directory entries. Being able to
+		 * open a file implies FILE_LIST_DIRECTORY.
+		 */
+
+		set_effective_capability(DAC_OVERRIDE_CAPABILITY);
+
+		ret = gpfswrap_get_winattrs(fsp->fh->fd, &attrs);
+		if (ret == -1) {
+			saved_errno = errno;
+		}
+
+		drop_effective_capability(DAC_OVERRIDE_CAPABILITY);
+
+		if (saved_errno != 0) {
+			errno = saved_errno;
+		}
+	}
+
 	if (ret == -1) {
 		DBG_WARNING("Getting winattrs failed for %s: %s\n",
 			    fsp->fsp_name->base_name, strerror(errno));