Mount flag MS_NOSUID in overlayfs has the same problem as MS_NOEXEC:
overlayfs opens files at underlying filesystem thus kernel check flags
at private clone of lower/upper mountpoint instead of overlayfs itself.
This patch saves MNT_NOSUID from overlayfs mount in file->f_mode when
opens file and checks it together with MNT_NOSUID. This behavior
stricter than usual: opened file stays nosuid even after remounting
overlayfs without MS_NOSUID but that should be fine.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
---
fs/exec.c | 3 ++-
fs/overlayfs/inode.c | 4 ++++
fs/overlayfs/super.c | 6 ++++++
include/linux/fs.h | 3 +++
security/commoncap.c | 3 ++-
security/selinux/hooks.c | 3 ++-
6 files changed, 19 insertions(+), 3 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 1977c2a553ac..0d81c6a43ef4 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1289,7 +1289,8 @@ static void bprm_fill_uid(struct linux_binprm *bprm)
bprm->cred->euid = current_euid();
bprm->cred->egid = current_egid();
- if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
+ if ((bprm->file->f_mode & FMODE_NOSUID) ||
+ (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID))
return;
if (task_no_new_privs(current))
diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index b9a40c8dbd1e..13be68335b1d 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -373,6 +373,10 @@ static int ovl_dentry_open(const struct path *path, struct file *file,
}
err = vfs_open(&realpath, file, cred);
+
+ if (path->mnt->mnt_flags & MNT_NOSUID)
+ file->f_mode |= FMODE_NOSUID;
+
out_drop_write:
if (want_write)
ovl_drop_write(dentry);
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 64c3714acf38..e5db31f78c7d 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -930,6 +930,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
if (!(ufs->upper_mnt->mnt_flags & MNT_LOCK_NOEXEC))
ufs->upper_mnt->mnt_flags &= ~MNT_NOEXEC;
+ if (!(ufs->upper_mnt->mnt_flags & MNT_LOCK_NOSUID))
+ ufs->upper_mnt->mnt_flags &= ~MNT_NOSUID;
+
ufs->workdir = ovl_workdir_create(ufs->upper_mnt, workpath.dentry);
err = PTR_ERR(ufs->workdir);
if (IS_ERR(ufs->workdir)) {
@@ -965,6 +968,9 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
if (!(mnt->mnt_flags & MNT_LOCK_NOEXEC))
mnt->mnt_flags &= ~MNT_NOEXEC;
+ if (!(mnt->mnt_flags & MNT_LOCK_NOSUID))
+ mnt->mnt_flags &= ~MNT_NOSUID;
+
ufs->lower_mnt[ufs->numlower] = mnt;
ufs->numlower++;
}
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 55c3edd9519e..abc5cd658ad0 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -136,6 +136,9 @@ typedef void (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
/* Has write method(s) */
#define FMODE_CAN_WRITE ((__force fmode_t)0x40000)
+/* Ignode S_ISUID and S_ISGID bits when executing this file */
+#define FMODE_NOSUID ((__force fmode_t)0x80000)
+
/* File was opened by fanotify and shouldn't generate fanotify events */
#define FMODE_NONOTIFY ((__force fmode_t)0x4000000)
diff --git a/security/commoncap.c b/security/commoncap.c
index d103f5a4043d..15deb600503b 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -437,7 +437,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
if (!file_caps_enabled)
return 0;
- if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
+ if ((bprm->file->f_mode & FMODE_NOSUID) ||
+ (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID))
return 0;
rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 623108199641..437e0e131fbd 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2137,7 +2137,8 @@ static int check_nnp_nosuid(const struct linux_binprm *bprm,
const struct task_security_struct *new_tsec)
{
int nnp = (bprm->unsafe & LSM_UNSAFE_NO_NEW_PRIVS);
- int nosuid = (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID);
+ int nosuid = (bprm->file->f_mode & FMODE_NOSUID) ||
+ (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID);
int rc;
if (!nnp && !nosuid)
--
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