Re: [PATCH v2] cred: Propagate security_prepare_creds() error code

Paul Moore
2022-05-27T20:05:47Z

On Wed, May 25, 2022 at 2:37 PM Frederick Lawler <fred@cloudflare.com> wrote:
>
> While experimenting with the security_prepare_creds() LSM hook, we
> noticed that our EPERM error code was not propagated up the callstack.
> Instead ENOMEM is always returned. As a result, some tools may send a
> confusing error message to the user:
>
> $ unshare -rU
> unshare: unshare failed: Cannot allocate memory
>
> A user would think that the system didn't have enough memory, when
> instead the action was denied.
>
> This problem occurs because prepare_creds() and prepare_kernel_cred()
> return NULL when security_prepare_creds() returns an error code. Later,
> functions calling prepare_creds() and prepare_kernel_cred() return
> ENOMEM because they assume that a NULL meant there was no memory
> allocated.
>
> Fix this by propagating an error code from security_prepare_creds() up
> the callstack.
>
> Signed-off-by: Frederick Lawler <fred@cloudflare.com>
>
> ---
> Changes since v1:
> - Revert style churn in ovl_create_or_link() noted by Amir
> - Revert style churn in prepare_nsset() noted by Serge
> - Update documentation for prepare_creds()
> - Set ofs->creator_cred in ovl_fill_super() and req->creds in aio_fsync()
> to NULL on error noted by Amir
> ---
> Documentation/security/credentials.rst | 6 +++---
> fs/aio.c | 9 +++++++--
> fs/cachefiles/security.c | 8 ++++----
> fs/cifs/cifs_spnego.c | 4 ++--
> fs/cifs/cifsacl.c | 4 ++--
> fs/coredump.c | 2 +-
> fs/exec.c | 14 ++++++++-----
> fs/ksmbd/smb_common.c | 4 ++--
> fs/nfs/flexfilelayout/flexfilelayout.c | 7 +++++--
> fs/nfs/nfs4idmap.c | 4 ++--
> fs/nfsd/auth.c | 4 ++--
> fs/nfsd/nfs4callback.c | 10 ++++-----
> fs/nfsd/nfs4recover.c | 4 ++--
> fs/nfsd/nfsfh.c | 4 ++--
> fs/open.c | 8 ++++----
> fs/overlayfs/dir.c | 6 ++++--
> fs/overlayfs/super.c | 6 ++++--
> kernel/capability.c | 4 ++--
> kernel/cred.c | 28 +++++++++++++++-----------
> kernel/groups.c | 4 ++--
> kernel/nsproxy.c | 9 ++++++++-
> kernel/sys.c | 28 +++++++++++++-------------
> kernel/trace/trace_events_user.c | 4 ++--
> kernel/umh.c | 5 +++--
> kernel/user_namespace.c | 6 ++++--
> net/dns_resolver/dns_key.c | 4 ++--
> security/apparmor/task.c | 12 +++++------
> security/commoncap.c | 20 +++++++++---------
> security/keys/keyctl.c | 8 ++++----
> security/keys/process_keys.c | 16 +++++++--------
> security/landlock/syscalls.c | 4 ++--
> security/selinux/hooks.c | 8 ++++----
> security/smack/smack_lsm.c | 8 ++++----
> security/smack/smackfs.c | 4 ++--
> 34 files changed, 153 insertions(+), 123 deletions(-)

The SELinux bits look fine to me.

Acked-by: Paul Moore <paul@paul-moore.com> (SELinux)

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