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Subject[PATCH v4 08/15] commoncap: Move cap_elevated calculation into bprm_set_creds
Date
Instead of a separate function, open-code the cap_elevated test, which
lets us entirely remove bprm->cap_effective (to use the local "effective"
variable instead), and more accurately examine euid/egid changes via the
existing local "is_setid".

The following LTP tests were run to validate the changes:

# ./runltp -f syscalls -s cap
# ./runltp -f securebits
# ./runltp -f cap_bounds
# ./runltp -f filecaps

All kernel selftests for capabilities and exec continue to pass as well.

Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: James Morris <james.l.morris@oracle.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
---
include/linux/binfmts.h | 3 ---
security/commoncap.c | 52 ++++++++++---------------------------------------
2 files changed, 10 insertions(+), 45 deletions(-)

diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index ebc4030fc6bb..b2c1563091e5 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -31,9 +31,6 @@ struct linux_binprm {
* binfmt_script/misc).
*/
called_set_creds:1,
- cap_effective:1;/* true if has elevated effective capabilities,
- * false if not; except for init which inherits
- * its parent's caps anyway */
/*
* True if most recent call to the commoncaps bprm_set_creds
* hook (due to multiple prepare_binprm() calls from the
diff --git a/security/commoncap.c b/security/commoncap.c
index abb6050c8083..d8e26fb9781d 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -285,15 +285,6 @@ int cap_capset(struct cred *new,
return 0;
}

-/*
- * Clear proposed capability sets for execve().
- */
-static inline void bprm_clear_caps(struct linux_binprm *bprm)
-{
- cap_clear(bprm->cred->cap_permitted);
- bprm->cap_effective = false;
-}
-
/**
* cap_inode_need_killpriv - Determine if inode change affects privileges
* @dentry: The inode/dentry in being changed with change marked ATTR_KILL_PRIV
@@ -443,7 +434,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
int rc = 0;
struct cpu_vfs_cap_data vcaps;

- bprm_clear_caps(bprm);
+ cap_clear(bprm->cred->cap_permitted);

if (!file_caps_enabled)
return 0;
@@ -476,13 +467,11 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c

out:
if (rc)
- bprm_clear_caps(bprm);
+ cap_clear(bprm->cred->cap_permitted);

return rc;
}

-static int is_secureexec(struct linux_binprm *bprm);
-
/**
* cap_bprm_set_creds - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
@@ -587,8 +576,6 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
if (WARN_ON(!cap_ambient_invariant_ok(new)))
return -EPERM;

- bprm->cap_effective = effective;
-
/*
* Audit candidate if current->cap_effective is set
*
@@ -617,35 +604,16 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
return -EPERM;

/* Check for privilege-elevated exec. */
- bprm->cap_elevated = is_secureexec(bprm);
-
- return 0;
-}
-
-/**
- * is_secureexec - Determine whether a secure execution is required
- * @bprm: The execution parameters
- *
- * Determine whether a secure execution is required, return 1 if it is, and 0
- * if it is not.
- *
- * The credentials have been committed by this point, and so are no longer
- * available through @bprm->cred.
- */
-static int is_secureexec(struct linux_binprm *bprm)
-{
- const struct cred *cred = bprm->cred;
- kuid_t root_uid = make_kuid(cred->user_ns, 0);
-
- if (!uid_eq(cred->uid, root_uid)) {
- if (bprm->cap_effective)
- return 1;
- if (!cap_issubset(cred->cap_permitted, cred->cap_ambient))
- return 1;
+ bprm->cap_elevated = 0;
+ if (is_setid) {
+ bprm->cap_elevated = 1;
+ } else if (!uid_eq(new->uid, root_uid)) {
+ if (effective ||
+ !cap_issubset(new->cap_permitted, new->cap_ambient))
+ bprm->cap_elevated = 1;
}

- return (!uid_eq(cred->euid, cred->uid) ||
- !gid_eq(cred->egid, cred->gid));
+ return 0;
}

/**
--
2.7.4
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