[PATCH 1/5] fs: Fix S_NOSEC handling

[Jan Kara <jack@xxxxxxx>]

file_remove_suid() could mistakenly set S_NOSEC inode bit when root was
modifying the file. As a result following writes to the file by ordinary
user would avoid clearing suid or sgid bits.

Fix the bug by checking actual mode bits before setting S_NOSEC.

CC: stable@xxxxxxxxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 fs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/inode.c b/fs/inode.c
index 26753ba7b6d6..f5e01704a5c8 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1631,7 +1631,8 @@ int file_remove_suid(struct file *file)
                error = security_inode_killpriv(dentry);
        if (!error && killsuid)
                error = __remove_suid(dentry, killsuid);
-       if (!error && (inode->i_sb->s_flags & MS_NOSEC))
+       if (!error && (inode->i_sb->s_flags & MS_NOSEC) &&
+           !is_sxid(inode->i_mode))
                inode->i_flags |= S_NOSEC;
 
        return error;
-- 
1.8.4.5