exec: Compute file based creds only once
Move the computation of creds from prepare_binfmt into begin_new_exec
so that the creds need only be computed once. This is just code
reorganization no semantic changes of any kind are made.
Moving the computation is safe. I have looked through the kernel and
verified none of the binfmts look at bprm->cred directly, and that
there are no helpers that look at bprm->cred indirectly. Which means
that it is not a problem to compute the bprm->cred later in the
execution flow as it is not used until it becomes current->cred.
A new function bprm_creds_from_file is added to contain the work that
needs to be done. bprm_creds_from_file first computes which file
bprm->executable or most likely bprm->file that the bprm->creds
will be computed from.
The funciton bprm_fill_uid is updated to receive the file instead of
accessing bprm->file. The now unnecessary work needed to reset the
bprm->cred->euid, and bprm->cred->egid is removed from brpm_fill_uid.
A small comment to document that bprm_fill_uid now only deals with the
work to handle suid and sgid files. The default case is already
heandled by prepare_exec_creds.
The function security_bprm_repopulate_creds is renamed
security_bprm_creds_from_file and now is explicitly passed the file
from which to compute the creds. The documentation of the
bprm_creds_from_file security hook is updated to explain when the hook
is called and what it needs to do. The file is passed from
cap_bprm_creds_from_file into get_file_caps so that the caps are
computed for the appropriate file. The now unnecessary work in
cap_bprm_creds_from_file to reset the ambient capabilites has been
removed. A small comment to document that the work of
cap_bprm_creds_from_file is to read capabilities from the files
secureity attribute and derive capabilities from the fact the
user had uid 0 has been added.
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
diff --git a/security/commoncap.c b/security/commoncap.c
index 6de72d2..59bf3c1 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -647,7 +647,8 @@ int get_vfs_caps_from_disk(const struct dentry *dentry, struct cpu_vfs_cap_data
* its xattrs and, if present, apply them to the proposed credentials being
* constructed by execve().
*/
-static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_fcap)
+static int get_file_caps(struct linux_binprm *bprm, struct file *file,
+ bool *effective, bool *has_fcap)
{
int rc = 0;
struct cpu_vfs_cap_data vcaps;
@@ -657,7 +658,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
if (!file_caps_enabled)
return 0;
- if (!mnt_may_suid(bprm->file->f_path.mnt))
+ if (!mnt_may_suid(file->f_path.mnt))
return 0;
/*
@@ -665,10 +666,10 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_f
* explicit that capability bits are limited to s_user_ns and its
* descendants.
*/
- if (!current_in_userns(bprm->file->f_path.mnt->mnt_sb->s_user_ns))
+ if (!current_in_userns(file->f_path.mnt->mnt_sb->s_user_ns))
return 0;
- rc = get_vfs_caps_from_disk(bprm->file->f_path.dentry, &vcaps);
+ rc = get_vfs_caps_from_disk(file->f_path.dentry, &vcaps);
if (rc < 0) {
if (rc == -EINVAL)
printk(KERN_NOTICE "Invalid argument reading file caps for %s\n",
@@ -797,26 +798,27 @@ static inline bool nonroot_raised_pE(struct cred *new, const struct cred *old,
}
/**
- * cap_bprm_repopulate_creds - Set up the proposed credentials for execve().
+ * cap_bprm_creds_from_file - Set up the proposed credentials for execve().
* @bprm: The execution parameters, including the proposed creds
+ * @file: The file to pull the credentials from
*
* Set up the proposed credentials for a new execution context being
* constructed by execve(). The proposed creds in @bprm->cred is altered,
* which won't take effect immediately. Returns 0 if successful, -ve on error.
*/
-int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
+int cap_bprm_creds_from_file(struct linux_binprm *bprm, struct file *file)
{
+ /* Process setpcap binaries and capabilities for uid 0 */
const struct cred *old = current_cred();
struct cred *new = bprm->cred;
bool effective = false, has_fcap = false, is_setid;
int ret;
kuid_t root_uid;
- new->cap_ambient = old->cap_ambient;
if (WARN_ON(!cap_ambient_invariant_ok(old)))
return -EPERM;
- ret = get_file_caps(bprm, &effective, &has_fcap);
+ ret = get_file_caps(bprm, file, &effective, &has_fcap);
if (ret < 0)
return ret;
@@ -826,7 +828,7 @@ int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
/* if we have fs caps, clear dangerous personality flags */
if (__cap_gained(permitted, new, old))
- bprm->pf_per_clear |= PER_CLEAR_ON_SETID;
+ bprm->per_clear |= PER_CLEAR_ON_SETID;
/* Don't let someone trace a set[ug]id/setpcap binary with the revised
* credentials unless they have the appropriate permit.
@@ -889,7 +891,7 @@ int cap_bprm_repopulate_creds(struct linux_binprm *bprm)
(!__is_real(root_uid, new) &&
(effective ||
__cap_grew(permitted, ambient, new))))
- bprm->active_secureexec = 1;
+ bprm->secureexec = 1;
return 0;
}
@@ -1346,7 +1348,7 @@ static struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(ptrace_traceme, cap_ptrace_traceme),
LSM_HOOK_INIT(capget, cap_capget),
LSM_HOOK_INIT(capset, cap_capset),
- LSM_HOOK_INIT(bprm_repopulate_creds, cap_bprm_repopulate_creds),
+ LSM_HOOK_INIT(bprm_creds_from_file, cap_bprm_creds_from_file),
LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
LSM_HOOK_INIT(inode_getsecurity, cap_inode_getsecurity),