CVE-2018-13405

Fix up non-directory creation in SGID directories

Reference:
https://nvd.nist.gov/vuln/detail/CVE-2018-13405
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=298243a5fb640f018e2fae22c0c895f1b27f0963

Change-Id: Ia5bb134fc9fecf9b9647197073f1a6bba7ae27eb
Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>

1 files changed, 53 insertions, 0 deletions

diff --git a/patches/cve/CVE-2018-13405-Fix-up-non-directory-creation-in-SGID-directories.patch b/patches/cve/CVE-2018-13405-Fix-up-non-directory-creation-in-SGID-directories.patch
new file mode 100644
index 0000000..d5eb1c0
--- /dev/null
+++ b/patches/cve/CVE-2018-13405-Fix-up-non-directory-creation-in-SGID-directories.patch
@@ -0,0 +1,53 @@
+From 298243a5fb640f018e2fae22c0c895f1b27f0963 Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Tue, 3 Jul 2018 17:10:19 -0700
+Subject: [PATCH] Fix up non-directory creation in SGID directories
+
+commit 0fa3ecd87848c9c93c2c828ef4c3a8ca36ce46c7 upstream.
+
+sgid directories have special semantics, making newly created files in
+the directory belong to the group of the directory, and newly created
+subdirectories will also become sgid.  This is historically used for
+group-shared directories.
+
+But group directories writable by non-group members should not imply
+that such non-group members can magically join the group, so make sure
+to clear the sgid bit on non-directories for non-members (but remember
+that sgid without group execute means "mandatory locking", just to
+confuse things even more).
+
+CVE: CVE-2018-13405
+Upstream-Status: Backport [https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?h=linux-4.14.y&id=298243a5fb640f018e2fae22c0c895f1b27f0963]
+
+Reported-by: Jann Horn <jannh@google.com>
+Cc: Andy Lutomirski <luto@kernel.org>
+Cc: Al Viro <viro@zeniv.linux.org.uk>
+Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+Signed-off-by: Andreas Wellving <andreas.wellving@enea.com>
+---
+ fs/inode.c | 6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/fs/inode.c b/fs/inode.c
+index e07b3e1f5970..cfc36d11bcb3 100644
+--- a/fs/inode.c
++++ b/fs/inode.c
+@@ -2006,8 +2006,14 @@ void inode_init_owner(struct inode *inode, const struct inode *dir,
+        inode->i_uid = current_fsuid();
+        if (dir && dir->i_mode & S_ISGID) {
+                inode->i_gid = dir->i_gid;
++
++               /* Directories are special, and always inherit S_ISGID */
+                if (S_ISDIR(mode))
+                        mode |= S_ISGID;
++               else if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP) &&
++                        !in_group_p(inode->i_gid) &&
++                        !capable_wrt_inode_uidgid(dir, CAP_FSETID))
++                       mode &= ~S_ISGID;
+        } else
+                inode->i_gid = current_fsgid();
+        inode->i_mode = mode;
+-- 
+2.20.1
+