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Groups > linux.kernel > #1700524
| From | Kees Cook <keescook@chromium.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | [PATCH v4 07/15] commoncap: Refactor to remove bprm_secureexec hook |
| Date | 2017-08-01 02:00 +0200 |
| Message-ID | <u9sLo-4eo-29@gated-at.bofh.it> (permalink) |
| References | <u9sLn-4eo-5@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
The commoncap implementation of the bprm_secureexec hook is the only LSM
that depends on the final call to its bprm_set_creds hook (since it may
be called for multiple files, it ignores bprm->called_set_creds). As a
result, it cannot safely _clear_ bprm->secureexec since other LSMs may
have set it. Instead, remove the bprm_secureexec hook by introducing a
new flag to bprm specific to commoncap: cap_elevated. This is similar to
cap_effective, but that is used for a specific subset of elevated
privileges, and exists solely to track state from bprm_set_creds to
bprm_secureexec. As such, it will be removed in the next patch.
Here, set the new bprm->cap_elevated flag when setuid/setgid has happened
from bprm_fill_uid() or fscapabilities have been prepared. This temporarily
moves the bprm_secureexec hook to a static inline. The helper will be
removed in the next patch; this makes the step easier to review and bisect,
since this does not introduce any changes to inputs nor outputs to the
"elevated privileges" calculation.
The new flag is merged with the bprm->secureexec flag in setup_new_exec()
since this marks the end of any further prepare_binprm() calls.
Cc: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Andy Lutomirski <luto@kernel.org>
Acked-by: James Morris <james.l.morris@oracle.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
---
fs/exec.c | 7 +++++++
include/linux/binfmts.h | 7 +++++++
security/commoncap.c | 12 ++++++++----
3 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 77244367c773..3762aef8b49e 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1324,6 +1324,13 @@ void setup_new_exec(struct linux_binprm * bprm)
{
bprm->secureexec |= security_bprm_secureexec(bprm);
+ /*
+ * Once here, prepare_binrpm() will not be called any more, so
+ * the final state of setuid/setgid/fscaps can be merged into the
+ * secureexec flag.
+ */
+ bprm->secureexec |= bprm->cap_elevated;
+
arch_pick_mmap_layout(current->mm);
current->sas_ss_sp = current->sas_ss_size = 0;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 6cfd36a27d4e..ebc4030fc6bb 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -35,6 +35,13 @@ struct linux_binprm {
* 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
+ * binfmt_script/misc handlers) resulted in elevated
+ * privileges.
+ */
+ cap_elevated:1,
+ /*
* Set by bprm_set_creds hook to indicate a privilege-gaining
* exec has happened. Used to sanitize execution environment
* and to set AT_SECURE auxv for glibc.
diff --git a/security/commoncap.c b/security/commoncap.c
index 7abebd782d5e..abb6050c8083 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -481,6 +481,8 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective, bool *has_c
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
@@ -614,11 +616,14 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
if (WARN_ON(!cap_ambient_invariant_ok(new)))
return -EPERM;
+ /* Check for privilege-elevated exec. */
+ bprm->cap_elevated = is_secureexec(bprm);
+
return 0;
}
/**
- * cap_bprm_secureexec - Determine whether a secure execution is required
+ * 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
@@ -627,9 +632,9 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
* The credentials have been committed by this point, and so are no longer
* available through @bprm->cred.
*/
-int cap_bprm_secureexec(struct linux_binprm *bprm)
+static int is_secureexec(struct linux_binprm *bprm)
{
- const struct cred *cred = current_cred();
+ const struct cred *cred = bprm->cred;
kuid_t root_uid = make_kuid(cred->user_ns, 0);
if (!uid_eq(cred->uid, root_uid)) {
@@ -1079,7 +1084,6 @@ struct security_hook_list capability_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(capget, cap_capget),
LSM_HOOK_INIT(capset, cap_capset),
LSM_HOOK_INIT(bprm_set_creds, cap_bprm_set_creds),
- LSM_HOOK_INIT(bprm_secureexec, cap_bprm_secureexec),
LSM_HOOK_INIT(inode_need_killpriv, cap_inode_need_killpriv),
LSM_HOOK_INIT(inode_killpriv, cap_inode_killpriv),
LSM_HOOK_INIT(mmap_addr, cap_mmap_addr),
--
2.7.4
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[PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 02/15] exec: Correct comments about "point of no return" Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 10/15] exec: Use secureexec for setting dumpability Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 10/15] exec: Use secureexec for setting dumpability James Morris <jmorris@namei.org> - 2017-08-01 02:50 +0200
[PATCH v4 08/15] commoncap: Move cap_elevated calculation into bprm_set_creds Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 08/15] commoncap: Move cap_elevated calculation into bprm_set_creds Andy Lutomirski <luto@kernel.org> - 2017-08-01 15:50 +0200
[PATCH v4 11/15] exec: Use secureexec for clearing pdeath_signal Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 05/15] selinux: Refactor to remove bprm_secureexec hook Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 05/15] selinux: Refactor to remove bprm_secureexec hook James Morris <jmorris@namei.org> - 2017-08-01 02:50 +0200
Re: [PATCH v4 05/15] selinux: Refactor to remove bprm_secureexec hook Andy Lutomirski <luto@kernel.org> - 2017-08-01 15:30 +0200
[PATCH v4 09/15] LSM: drop bprm_secureexec hook Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 01/15] exec: Rename bprm->cred_prepared to called_set_creds Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 03/15] binfmt: Introduce secureexec flag Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 03/15] binfmt: Introduce secureexec flag Kees Cook <keescook@chromium.org> - 2017-08-01 02:30 +0200
Re: [PATCH v4 03/15] binfmt: Introduce secureexec flag James Morris <jmorris@namei.org> - 2017-08-01 02:50 +0200
[PATCH v4 06/15] smack: Refactor to remove bprm_secureexec hook Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 06/15] smack: Refactor to remove bprm_secureexec hook James Morris <jmorris@namei.org> - 2017-08-01 02:50 +0200
Re: [PATCH v4 06/15] smack: Refactor to remove bprm_secureexec hook Casey Schaufler <casey@schaufler-ca.com> - 2017-08-01 17:30 +0200
[PATCH v4 07/15] commoncap: Refactor to remove bprm_secureexec hook Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 04/15] apparmor: Refactor to remove bprm_secureexec hook Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 13/15] exec: Consolidate dumpability logic Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
[PATCH v4 12/15] smack: Remove redundant pdeath_signal clearing Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 12/15] smack: Remove redundant pdeath_signal clearing James Morris <jmorris@namei.org> - 2017-08-01 03:00 +0200
Re: [PATCH v4 12/15] smack: Remove redundant pdeath_signal clearing Casey Schaufler <casey@schaufler-ca.com> - 2017-08-01 17:30 +0200
[PATCH v4 15/15] exec: Consolidate pdeath_signal clearing Kees Cook <keescook@chromium.org> - 2017-08-01 02:00 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 02:40 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec James Morris <jmorris@namei.org> - 2017-08-01 03:00 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 05:10 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-01 07:20 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-01 07:20 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 17:10 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Linus Torvalds <torvalds@linux-foundation.org> - 2017-08-01 22:20 +0200
Re: [PATCH v4 00/15] exec: Use sane stack rlimit under secureexec Kees Cook <keescook@chromium.org> - 2017-08-01 23:10 +0200
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