| Message ID | 1500416736-49829-2-git-send-email-keescook@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 07/18/2017 03:25 PM, Kees Cook wrote: > The bprm_secureexec hook can be moved earlier. Right now, it is called > during create_elf_tables(), via load_binary(), via search_binary_handler(), > via exec_binprm(). Nearly all (see exception below) state used by > bprm_secureexec is created during the bprm_set_creds hook, called from > prepare_binprm(). > > For all LSMs (except commoncaps described next), only the first execution > of bprm_set_creds takes any effect (they all check bprm->cred_prepared which > prepare_binprm() sets after the first call to the bprm_set_creds hook). > However, all these LSMs also only do anything with bprm_secureexec when > they detected a secure state during their first run of bprm_set_creds. > Therefore, it is functionally identical to move the detection into > bprm_set_creds, since the results from secureexec here only need to be > based on the first call to the LSM's bprm_set_creds hook. > > The single exception is that the commoncaps secureexec hook also examines > euid/uid and egid/gid differences which are controlled by bprm_fill_uid(), > via prepare_binprm(), which can be called multiple times (e.g. > binfmt_script, binfmt_misc), and may clear the euid/egid for the final > load (i.e. the script interpreter). However, while commoncaps specifically > ignores bprm->cred_prepared, and runs its bprm_set_creds hook each time > prepare_binprm() may get called, it needs to base the secureexec decision > on the final call to bprm_set_creds. As a result, it will need special > handling. > > To begin this refactoring, this adds the secureexec flag to the bprm > struct, which will eventually be used in place of the LSM hook. > > Cc: David Howells <dhowells@redhat.com> > Signed-off-by: Kees Cook <keescook@chromium.org> looks good Reviewed-by: John Johansen <john.johansen@canonical.com> > --- > fs/binfmt_elf.c | 3 ++- > fs/binfmt_elf_fdpic.c | 3 ++- > include/linux/binfmts.h | 8 +++++++- > 3 files changed, 11 insertions(+), 3 deletions(-) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 5075fd5c62c8..991e4de3515f 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -254,7 +254,8 @@ 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)); > + bprm->secureexec |= 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..c88b35d4a6b3 100644 > --- a/fs/binfmt_elf_fdpic.c > +++ b/fs/binfmt_elf_fdpic.c > @@ -650,7 +650,8 @@ 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)); > + bprm->secureexec |= security_bprm_secureexec(bprm); > + NEW_AUX_ENT(AT_SECURE, bprm->secureexec); > NEW_AUX_ENT(AT_EXECFN, bprm->exec); > > #ifdef ARCH_DLINFO > diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h > index 05488da3aee9..9508b5f83c7e 100644 > --- a/include/linux/binfmts.h > +++ b/include/linux/binfmts.h > @@ -27,9 +27,15 @@ 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 */ > + /* > + * 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. > + */ > + secureexec:1; > #ifdef __alpha__ > unsigned int taso:1; > #endif >
On Tue, Jul 18, 2017 at 3:25 PM, Kees Cook <keescook@chromium.org> wrote: > To begin this refactoring, this adds the secureexec flag to the bprm > struct, which will eventually be used in place of the LSM hook. I'm very confused. See below. Maybe a later patch will unconfuse me. > > Cc: David Howells <dhowells@redhat.com> > Signed-off-by: Kees Cook <keescook@chromium.org> > --- > fs/binfmt_elf.c | 3 ++- > fs/binfmt_elf_fdpic.c | 3 ++- > include/linux/binfmts.h | 8 +++++++- > 3 files changed, 11 insertions(+), 3 deletions(-) > > diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c > index 5075fd5c62c8..991e4de3515f 100644 > --- a/fs/binfmt_elf.c > +++ b/fs/binfmt_elf.c > @@ -254,7 +254,8 @@ 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)); > + bprm->secureexec |= security_bprm_secureexec(bprm); > + NEW_AUX_ENT(AT_SECURE, bprm->secureexec); This is ->load_binary ... > diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h > index 05488da3aee9..9508b5f83c7e 100644 > --- a/include/linux/binfmts.h > +++ b/include/linux/binfmts.h > @@ -27,9 +27,15 @@ 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 */ > + /* > + * 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. > + */ ... which is not bprm_set_creds(). What am I missing here?
diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c index 5075fd5c62c8..991e4de3515f 100644 --- a/fs/binfmt_elf.c +++ b/fs/binfmt_elf.c @@ -254,7 +254,8 @@ 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)); + bprm->secureexec |= 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..c88b35d4a6b3 100644 --- a/fs/binfmt_elf_fdpic.c +++ b/fs/binfmt_elf_fdpic.c @@ -650,7 +650,8 @@ 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)); + bprm->secureexec |= security_bprm_secureexec(bprm); + NEW_AUX_ENT(AT_SECURE, bprm->secureexec); NEW_AUX_ENT(AT_EXECFN, bprm->exec); #ifdef ARCH_DLINFO diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h index 05488da3aee9..9508b5f83c7e 100644 --- a/include/linux/binfmts.h +++ b/include/linux/binfmts.h @@ -27,9 +27,15 @@ 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 */ + /* + * 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. + */ + secureexec:1; #ifdef __alpha__ unsigned int taso:1; #endif
The bprm_secureexec hook can be moved earlier. Right now, it is called during create_elf_tables(), via load_binary(), via search_binary_handler(), via exec_binprm(). Nearly all (see exception below) state used by bprm_secureexec is created during the bprm_set_creds hook, called from prepare_binprm(). For all LSMs (except commoncaps described next), only the first execution of bprm_set_creds takes any effect (they all check bprm->cred_prepared which prepare_binprm() sets after the first call to the bprm_set_creds hook). However, all these LSMs also only do anything with bprm_secureexec when they detected a secure state during their first run of bprm_set_creds. Therefore, it is functionally identical to move the detection into bprm_set_creds, since the results from secureexec here only need to be based on the first call to the LSM's bprm_set_creds hook. The single exception is that the commoncaps secureexec hook also examines euid/uid and egid/gid differences which are controlled by bprm_fill_uid(), via prepare_binprm(), which can be called multiple times (e.g. binfmt_script, binfmt_misc), and may clear the euid/egid for the final load (i.e. the script interpreter). However, while commoncaps specifically ignores bprm->cred_prepared, and runs its bprm_set_creds hook each time prepare_binprm() may get called, it needs to base the secureexec decision on the final call to bprm_set_creds. As a result, it will need special handling. To begin this refactoring, this adds the secureexec flag to the bprm struct, which will eventually be used in place of the LSM hook. Cc: David Howells <dhowells@redhat.com> Signed-off-by: Kees Cook <keescook@chromium.org> --- fs/binfmt_elf.c | 3 ++- fs/binfmt_elf_fdpic.c | 3 ++- include/linux/binfmts.h | 8 +++++++- 3 files changed, 11 insertions(+), 3 deletions(-)