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Groups > linux.kernel > #1505726

[PATCH 4.7 20/45] fuse: fix killing s[ug]id in setattr

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4.7-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@redhat.com>

commit a09f99eddef44035ec764075a37bace8181bec38 upstream.

Fuse allowed VFS to set mode in setattr in order to clear suid/sgid on
chown and truncate, and (since writeback_cache) write.  The problem with
this is that it'll potentially restore a stale mode.

The poper fix would be to let the filesystems do the suid/sgid clearing on
the relevant operations.  Possibly some are already doing it but there's no
way we can detect this.

So fix this by refreshing and recalculating the mode.  Do this only if
ATTR_KILL_S[UG]ID is set to not destroy performance for writes.  This is
still racy but the size of the window is reduced.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/fuse/dir.c |   32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1701,16 +1701,40 @@ error:
 static int fuse_setattr(struct dentry *entry, struct iattr *attr)
 {
 	struct inode *inode = d_inode(entry);
+	struct file *file = (attr->ia_valid & ATTR_FILE) ? attr->ia_file : NULL;
 	int ret;
 
 	if (!fuse_allow_current_process(get_fuse_conn(inode)))
 		return -EACCES;
 
-	if (attr->ia_valid & ATTR_FILE)
-		ret = fuse_do_setattr(inode, attr, attr->ia_file);
-	else
-		ret = fuse_do_setattr(inode, attr, NULL);
+	if (attr->ia_valid & (ATTR_KILL_SUID | ATTR_KILL_SGID)) {
+		int kill;
 
+		attr->ia_valid &= ~(ATTR_KILL_SUID | ATTR_KILL_SGID |
+				    ATTR_MODE);
+		/*
+		 * ia_mode calculation may have used stale i_mode.  Refresh and
+		 * recalculate.
+		 */
+		ret = fuse_do_getattr(inode, NULL, file);
+		if (ret)
+			return ret;
+
+		attr->ia_mode = inode->i_mode;
+		kill = should_remove_suid(entry);
+		if (kill & ATTR_KILL_SUID) {
+			attr->ia_valid |= ATTR_MODE;
+			attr->ia_mode &= ~S_ISUID;
+		}
+		if (kill & ATTR_KILL_SGID) {
+			attr->ia_valid |= ATTR_MODE;
+			attr->ia_mode &= ~S_ISGID;
+		}
+	}
+	if (!attr->ia_valid)
+		return 0;
+
+	ret = fuse_do_setattr(inode, attr, file);
 	if (!ret) {
 		/* Directory mode changed, may need to revalidate access */
 		if (d_is_dir(entry) && (attr->ia_valid & ATTR_MODE))

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[PATCH 4.7 00/45] 4.7.10-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 06/45] debugfs: introduce a public file_operations accessor Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 44/45] cachefiles: Fix attempt to read i_blocks after deleting file [ver #2] Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 38/45] ext4: release bh in make_indexed_dir Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 33/45] ext4: enforce online defrag restriction for encrypted files Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 45/45] cfq: fix starvation of asynchronous writes Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 08/45] b43legacy: fix debugfs crash Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:40 +0200
  [PATCH 4.7 20/45] fuse: fix killing s[ug]id in setattr Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 21/45] i40e: avoid NULL pointer dereference and recursive errors on early PCI error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 14/45] drivers: base: dma-mapping: page align the size when unmap_kernel_range Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 02/45] serial: 8250_dw: Check the data->pclk when get apb_pclk Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 30/45] scsi: arcmsr: Simplify user_len checking Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 29/45] scsi: arcmsr: Buffer overflow in arcmsr_iop_message_xfer() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 05/45] ARCv2: fix local_save_flags Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 17/45] clk: mvebu: dynamically allocate resources in Armada CP110 system controller Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 23/45] brcmfmac: fix pmksa->bssid usage Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  [PATCH 4.7 15/45] IB/hfi1: Fix defered ack race with qp destroy Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-21 11:50 +0200
  Re: [PATCH 4.7 00/45] 4.7.10-stable review Shuah Khan <shuah.kh@samsung.com> - 2016-10-21 17:50 +0200
  Re: [PATCH 4.7 00/45] 4.7.10-stable review Guenter Roeck <linux@roeck-us.net> - 2016-10-21 21:20 +0200
  Re: [PATCH 4.7 00/45] 4.7.10-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-10-22 12:00 +0200

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