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Subject[PATCH 1/2] exec: Move security_bprm_secureexec() earlier
Date
There are several places where exec needs to know if a privilege-gain
has happened. Right now it only checks uid/euid differences, though
capabilities could have been elevated too. This moves the secureexec
check ahead of committing credentials, and retains the value for later
examination. A resulting redundant case of clearing pdeath_signal is
also removed from Smack, and commoncap is updated to examine bprm->cred
instead of current->cred.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
fs/binfmt_elf.c | 2 +-
fs/binfmt_elf_fdpic.c | 2 +-
fs/exec.c | 15 ++++++++++-----
include/linux/binfmts.h | 3 ++-
include/linux/lsm_hooks.h | 3 ++-
security/commoncap.c | 4 +---
security/smack/smack_lsm.c | 15 ---------------
7 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 5075fd5c62c8..7f6ec4dac13d 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -254,7 +254,7 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid));
NEW_AUX_ENT(AT_GID, from_kgid_munged(cred->user_ns, cred->gid));
NEW_AUX_ENT(AT_EGID, from_kgid_munged(cred->user_ns, cred->egid));
- NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_SECURE, bprm->secureexec);
NEW_AUX_ENT(AT_RANDOM, (elf_addr_t)(unsigned long)u_rand_bytes);
#ifdef ELF_HWCAP2
NEW_AUX_ENT(AT_HWCAP2, ELF_HWCAP2);
diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
index cf93a4fad012..5aa9199dfb13 100644
--- a/fs/binfmt_elf_fdpic.c
+++ b/fs/binfmt_elf_fdpic.c
@@ -650,7 +650,7 @@ static int create_elf_fdpic_tables(struct linux_binprm *bprm,
NEW_AUX_ENT(AT_EUID, (elf_addr_t) from_kuid_munged(cred->user_ns, cred->euid));
NEW_AUX_ENT(AT_GID, (elf_addr_t) from_kgid_munged(cred->user_ns, cred->gid));
NEW_AUX_ENT(AT_EGID, (elf_addr_t) from_kgid_munged(cred->user_ns, cred->egid));
- NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_SECURE, bprm->secureexec);
NEW_AUX_ENT(AT_EXECFN, bprm->exec);

#ifdef ARCH_DLINFO
diff --git a/fs/exec.c b/fs/exec.c
index ddca2cf15f71..1e8d647d8e7c 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1330,12 +1330,18 @@ EXPORT_SYMBOL(would_dump);

void setup_new_exec(struct linux_binprm * bprm)
{
+ /* This is the point of no return */
+
+ if (security_bprm_secureexec(bprm)) {
+ /* Record for AT_SECURE. */
+ bprm->secureexec = 1;
+ }
+
arch_pick_mmap_layout(current->mm);

- /* This is the point of no return */
current->sas_ss_sp = current->sas_ss_size = 0;

- if (uid_eq(current_euid(), current_uid()) && gid_eq(current_egid(), current_gid()))
+ if (!bprm->secureexec)
set_dumpable(current->mm, SUID_DUMP_USER);
else
set_dumpable(current->mm, suid_dumpable);
@@ -1350,9 +1356,8 @@ void setup_new_exec(struct linux_binprm * bprm)
*/
current->mm->task_size = TASK_SIZE;

- /* install the new credentials */
- if (!uid_eq(bprm->cred->uid, current_euid()) ||
- !gid_eq(bprm->cred->gid, current_egid())) {
+ /* prepare to install the new credentials */
+ if (bprm->secureexec) {
current->pdeath_signal = 0;
} else {
if (bprm->interp_flags & BINPRM_FLAGS_ENFORCE_NONDUMP)
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index 05488da3aee9..1afaa303cad0 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -27,9 +27,10 @@ struct linux_binprm {
unsigned int
cred_prepared:1,/* true if creds already prepared (multiple
* preps happen for interpreters) */
- cap_effective:1;/* true if has elevated effective capabilities,
+ cap_effective:1,/* true if has elevated effective capabilities,
* false if not; except for init which inherits
* its parent's caps anyway */
+ secureexec:1; /* true when gaining privileges */
#ifdef __alpha__
unsigned int taso:1;
#endif
diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 080f34e66017..d1bd24fb4a33 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -72,7 +72,8 @@
* Return a boolean value (0 or 1) indicating whether a "secure exec"
* is required. The flag is passed in the auxiliary table
* on the initial stack to the ELF interpreter to indicate whether libc
- * should enable secure mode.
+ * should enable secure mode. Called before bprm_committing_creds(),
+ * so pending credentials are in @bprm->cred.
* @bprm contains the linux_binprm structure.
*
* Security hooks for filesystem operations.
diff --git a/security/commoncap.c b/security/commoncap.c
index 7abebd782d5e..482d3aac2fc6 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -624,12 +624,10 @@ int cap_bprm_set_creds(struct linux_binprm *bprm)
* 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.
*/
int cap_bprm_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)) {
diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
index 658f5d8c7e76..0c89afcb24c4 100644
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -954,20 +954,6 @@ static int smack_bprm_set_creds(struct linux_binprm *bprm)
}

/**
- * smack_bprm_committing_creds - Prepare to install the new credentials
- * from bprm.
- *
- * @bprm: binprm for exec
- */
-static void smack_bprm_committing_creds(struct linux_binprm *bprm)
-{
- struct task_smack *bsp = bprm->cred->security;
-
- if (bsp->smk_task != bsp->smk_forked)
- current->pdeath_signal = 0;
-}
-
-/**
* smack_bprm_secureexec - Return the decision to use secureexec.
* @bprm: binprm for exec
*
@@ -4645,7 +4631,6 @@ static struct security_hook_list smack_hooks[] __lsm_ro_after_init = {
LSM_HOOK_INIT(sb_parse_opts_str, smack_parse_opts_str),

LSM_HOOK_INIT(bprm_set_creds, smack_bprm_set_creds),
- LSM_HOOK_INIT(bprm_committing_creds, smack_bprm_committing_creds),
LSM_HOOK_INIT(bprm_secureexec, smack_bprm_secureexec),

LSM_HOOK_INIT(inode_alloc_security, smack_inode_alloc_security),
--
2.7.4
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