[PATCH 04/11] fs: Don't remove suid for CAP_FSETID for userns root

[Dongsu Park]

From: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>

Expand the check in should_remove_suid() to keep privileges for
CAP_FSETID in s_user_ns rather than init_user_ns.

Patch v4 is available: https://patchwork.kernel.org/patch/8944621/

--EWB Changed from ns_capable(sb->s_user_ns, ) to capable_wrt_inode_uidgid

Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Serge Hallyn <serge@xxxxxxxxxx>
Signed-off-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Signed-off-by: Dongsu Park <dongsu@xxxxxxxxxx>
---
 fs/inode.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index fd401028..6459a437 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1749,7 +1749,8 @@ EXPORT_SYMBOL(touch_atime);
  */
 int should_remove_suid(struct dentry *dentry)
 {
-	umode_t mode = d_inode(dentry)->i_mode;
+	struct inode *inode = d_inode(dentry);
+	umode_t mode = inode->i_mode;
 	int kill = 0;
 
 	/* suid always must be killed */
@@ -1763,7 +1764,8 @@ int should_remove_suid(struct dentry *dentry)
 	if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
 		kill |= ATTR_KILL_SGID;
 
-	if (unlikely(kill && !capable(CAP_FSETID) && S_ISREG(mode)))
+	if (unlikely(kill && !capable_wrt_inode_uidgid(inode, CAP_FSETID) &&
+		     S_ISREG(mode)))
 		return kill;
 
 	return 0;
-- 
2.13.6