From a6f76f23d297f70e2a6b3ec607f7aeeea9e37e8d Mon Sep 17 00:00:00 2001 From: David Howells Date: Fri, 14 Nov 2008 10:39:24 +1100 Subject: CRED: Make execve() take advantage of copy-on-write credentials Make execve() take advantage of copy-on-write credentials, allowing it to set up the credentials in advance, and then commit the whole lot after the point of no return. This patch and the preceding patches have been tested with the LTP SELinux testsuite. This patch makes several logical sets of alteration: (1) execve(). The credential bits from struct linux_binprm are, for the most part, replaced with a single credentials pointer (bprm->cred). This means that all the creds can be calculated in advance and then applied at the point of no return with no possibility of failure. I would like to replace bprm->cap_effective with: cap_isclear(bprm->cap_effective) but this seems impossible due to special behaviour for processes of pid 1 (they always retain their parent's capability masks where normally they'd be changed - see cap_bprm_set_creds()). The following sequence of events now happens: (a) At the start of do_execve, the current task's cred_exec_mutex is locked to prevent PTRACE_ATTACH from obsoleting the calculation of creds that we make. (a) prepare_exec_creds() is then called to make a copy of the current task's credentials and prepare it. This copy is then assigned to bprm->cred. This renders security_bprm_alloc() and security_bprm_free() unnecessary, and so they've been removed. (b) The determination of unsafe execution is now performed immediately after (a) rather than later on in the code. The result is stored in bprm->unsafe for future reference. (c) prepare_binprm() is called, possibly multiple times. (i) This applies the result of set[ug]id binaries to the new creds attached to bprm->cred. Personality bit clearance is recorded, but now deferred on the basis that the exec procedure may yet fail. (ii) This then calls the new security_bprm_set_creds(). This should calculate the new LSM and capability credentials into *bprm->cred. This folds together security_bprm_set() and parts of security_bprm_apply_creds() (these two have been removed). Anything that might fail must be done at this point. (iii) bprm->cred_prepared is set to 1. bprm->cred_prepared is 0 on the first pass of the security calculations, and 1 on all subsequent passes. This allows SELinux in (ii) to base its calculations only on the initial script and not on the interpreter. (d) flush_old_exec() is called to commit the task to execution. This performs the following steps with regard to credentials: (i) Clear pdeath_signal and set dumpable on certain circumstances that may not be covered by commit_creds(). (ii) Clear any bits in current->personality that were deferred from (c.i). (e) install_exec_creds() [compute_creds() as was] is called to install the new credentials. This performs the following steps with regard to credentials: (i) Calls security_bprm_committing_creds() to apply any security requirements, such as flushing unauthorised files in SELinux, that must be done before the credentials are changed. This is made up of bits of security_bprm_apply_creds() and security_bprm_post_apply_creds(), both of which have been removed. This function is not allowed to fail; anything that might fail must have been done in (c.ii). (ii) Calls commit_creds() to apply the new credentials in a single assignment (more or less). Possibly pdeath_signal and dumpable should be part of struct creds. (iii) Unlocks the task's cred_replace_mutex, thus allowing PTRACE_ATTACH to take place. (iv) Clears The bprm->cred pointer as the credentials it was holding are now immutable. (v) Calls security_bprm_committed_creds() to apply any security alterations that must be done after the creds have been changed. SELinux uses this to flush signals and signal handlers. (f) If an error occurs before (d.i), bprm_free() will call abort_creds() to destroy the proposed new credentials and will then unlock cred_replace_mutex. No changes to the credentials will have been made. (2) LSM interface. A number of functions have been changed, added or removed: (*) security_bprm_alloc(), ->bprm_alloc_security() (*) security_bprm_free(), ->bprm_free_security() Removed in favour of preparing new credentials and modifying those. (*) security_bprm_apply_creds(), ->bprm_apply_creds() (*) security_bprm_post_apply_creds(), ->bprm_post_apply_creds() Removed; split between security_bprm_set_creds(), security_bprm_committing_creds() and security_bprm_committed_creds(). (*) security_bprm_set(), ->bprm_set_security() Removed; folded into security_bprm_set_creds(). (*) security_bprm_set_creds(), ->bprm_set_creds() New. The new credentials in bprm->creds should be checked and set up as appropriate. bprm->cred_prepared is 0 on the first call, 1 on the second and subsequent calls. (*) security_bprm_committing_creds(), ->bprm_committing_creds() (*) security_bprm_committed_creds(), ->bprm_committed_creds() New. Apply the security effects of the new credentials. This includes closing unauthorised files in SELinux. This function may not fail. When the former is called, the creds haven't yet been applied to the process; when the latter is called, they have. The former may access bprm->cred, the latter may not. (3) SELinux. SELinux has a number of changes, in addition to those to support the LSM interface changes mentioned above: (a) The bprm_security_struct struct has been removed in favour of using the credentials-under-construction approach. (c) flush_unauthorized_files() now takes a cred pointer and passes it on to inode_has_perm(), file_has_perm() and dentry_open(). Signed-off-by: David Howells Acked-by: James Morris Acked-by: Serge Hallyn Signed-off-by: James Morris --- arch/x86/ia32/ia32_aout.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_aout.c b/arch/x86/ia32/ia32_aout.c index 127ec3f07214..2a4d073d2cf1 100644 --- a/arch/x86/ia32/ia32_aout.c +++ b/arch/x86/ia32/ia32_aout.c @@ -327,7 +327,7 @@ static int load_aout_binary(struct linux_binprm *bprm, struct pt_regs *regs) current->mm->cached_hole_size = 0; current->mm->mmap = NULL; - compute_creds(bprm); + install_exec_creds(bprm); current->flags &= ~PF_FORKNOEXEC; if (N_MAGIC(ex) == OMAGIC) { -- cgit v1.2.2 From d0b48ca189523b638d8674fa41e94d1950a17038 Mon Sep 17 00:00:00 2001 From: Hiroshi Shimamoto Date: Tue, 16 Dec 2008 14:03:36 -0800 Subject: x86: ia32_signal: use __put_user() instead of __copy_to_user() Impact: cleanup __put_user() can be used for constant size 8, like arch/x86/kernel/signal.c. Signed-off-by: Hiroshi Shimamoto Signed-off-by: Ingo Molnar --- arch/x86/ia32/ia32_signal.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 1267977e7708..e4f2a5045743 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -467,7 +467,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka, * These are actually not used anymore, but left because some * gdb versions depend on them as a marker. */ - err |= __copy_to_user(frame->retcode, &code, 8); + err |= __put_user(*((u64 *)&code), (u64 *)frame->retcode); if (err) return -EFAULT; @@ -554,7 +554,7 @@ int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info, * Not actually used anymore, but left because some gdb * versions need it. */ - err |= __copy_to_user(frame->retcode, &code, 8); + err |= __put_user(*((u64 *)&code), (u64 *)frame->retcode); if (err) return -EFAULT; -- cgit v1.2.2 From 8bee3f0a662ad9c3d6bb705b0530a3b90f089c55 Mon Sep 17 00:00:00 2001 From: Hiroshi Shimamoto Date: Tue, 16 Dec 2008 14:04:43 -0800 Subject: x86: ia32_signal: use proper macro __USER32_DS Impact: cleanup Use __USER32_DS instead of __USER_DS in ia32_signal.c. No impact, because __USER32_DS is defined __USER_DS. Signed-off-by: Hiroshi Shimamoto Signed-off-by: Ingo Molnar --- arch/x86/ia32/ia32_signal.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index e4f2a5045743..9c99c429a20d 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -396,7 +396,7 @@ static void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, } /* This is the legacy signal stack switching. */ - else if ((regs->ss & 0xffff) != __USER_DS && + else if ((regs->ss & 0xffff) != __USER32_DS && !(ka->sa.sa_flags & SA_RESTORER) && ka->sa.sa_restorer) sp = (unsigned long) ka->sa.sa_restorer; -- cgit v1.2.2 From 3b0d29ee1c73b6b90bfddd10f7b8e86632b6b694 Mon Sep 17 00:00:00 2001 From: Hiroshi Shimamoto Date: Wed, 17 Dec 2008 18:51:46 -0800 Subject: x86: ia32_signal: rename struct sigframe and rt_sigframe Impact: cleanup, prepare to include sigframe.h Rename struct sigframe to struct sigframe_ia32 and struct rt_sigframe to struct rt_sigframe_ia32. Signed-off-by: Hiroshi Shimamoto Signed-off-by: Ingo Molnar --- arch/x86/ia32/ia32_signal.c | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 9c99c429a20d..334a4aa2e75b 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -174,7 +174,7 @@ asmlinkage long sys32_sigaltstack(const stack_ia32_t __user *uss_ptr, * Do a signal return; undo the signal stack. */ -struct sigframe +struct sigframe_ia32 { u32 pretcode; int sig; @@ -185,7 +185,7 @@ struct sigframe /* fp state follows here */ }; -struct rt_sigframe +struct rt_sigframe_ia32 { u32 pretcode; int sig; @@ -271,7 +271,7 @@ static int ia32_restore_sigcontext(struct pt_regs *regs, asmlinkage long sys32_sigreturn(struct pt_regs *regs) { - struct sigframe __user *frame = (struct sigframe __user *)(regs->sp-8); + struct sigframe_ia32 __user *frame = (struct sigframe_ia32 __user *)(regs->sp-8); sigset_t set; unsigned int ax; @@ -301,12 +301,12 @@ badframe: asmlinkage long sys32_rt_sigreturn(struct pt_regs *regs) { - struct rt_sigframe __user *frame; + struct rt_sigframe_ia32 __user *frame; sigset_t set; unsigned int ax; struct pt_regs tregs; - frame = (struct rt_sigframe __user *)(regs->sp - 4); + frame = (struct rt_sigframe_ia32 __user *)(regs->sp - 4); if (!access_ok(VERIFY_READ, frame, sizeof(*frame))) goto badframe; @@ -418,7 +418,7 @@ static void __user *get_sigframe(struct k_sigaction *ka, struct pt_regs *regs, int ia32_setup_frame(int sig, struct k_sigaction *ka, compat_sigset_t *set, struct pt_regs *regs) { - struct sigframe __user *frame; + struct sigframe_ia32 __user *frame; void __user *restorer; int err = 0; void __user *fpstate = NULL; @@ -497,7 +497,7 @@ int ia32_setup_frame(int sig, struct k_sigaction *ka, int ia32_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info, compat_sigset_t *set, struct pt_regs *regs) { - struct rt_sigframe __user *frame; + struct rt_sigframe_ia32 __user *frame; void __user *restorer; int err = 0; void __user *fpstate = NULL; -- cgit v1.2.2 From d98f9d84422c393103dc7569dc8444bac628f7ac Mon Sep 17 00:00:00 2001 From: Hiroshi Shimamoto Date: Wed, 17 Dec 2008 18:52:45 -0800 Subject: x86: ia32_signal: use sigframe.h Impact: cleanup Use arch/x86/include/asm/sigframe.h instead of defining redundant structures. Signed-off-by: Hiroshi Shimamoto Signed-off-by: Ingo Molnar --- arch/x86/ia32/ia32_signal.c | 26 ++------------------------ 1 file changed, 2 insertions(+), 24 deletions(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 334a4aa2e75b..3b3878a63bc2 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -32,6 +32,8 @@ #include #include +#include + #define DEBUG_SIG 0 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP))) @@ -173,30 +175,6 @@ asmlinkage long sys32_sigaltstack(const stack_ia32_t __user *uss_ptr, /* * Do a signal return; undo the signal stack. */ - -struct sigframe_ia32 -{ - u32 pretcode; - int sig; - struct sigcontext_ia32 sc; - struct _fpstate_ia32 fpstate_unused; /* look at kernel/sigframe.h */ - unsigned int extramask[_COMPAT_NSIG_WORDS-1]; - char retcode[8]; - /* fp state follows here */ -}; - -struct rt_sigframe_ia32 -{ - u32 pretcode; - int sig; - u32 pinfo; - u32 puc; - compat_siginfo_t info; - struct ucontext_ia32 uc; - char retcode[8]; - /* fp state follows here */ -}; - #define COPY(x) { \ err |= __get_user(regs->x, &sc->x); \ } -- cgit v1.2.2 From 8403295e0fa460f6240e2d781e25dc29189f33c7 Mon Sep 17 00:00:00 2001 From: Hiroshi Shimamoto Date: Fri, 19 Dec 2008 14:25:50 -0800 Subject: x86: ia32_signal: remove unnecessary declaration Impact: cleanup No need to declare do_signal(). Signed-off-by: Hiroshi Shimamoto Signed-off-by: Ingo Molnar --- arch/x86/ia32/ia32_signal.c | 1 - 1 file changed, 1 deletion(-) (limited to 'arch/x86/ia32') diff --git a/arch/x86/ia32/ia32_signal.c b/arch/x86/ia32/ia32_signal.c index 3b3878a63bc2..09513f8a2896 100644 --- a/arch/x86/ia32/ia32_signal.c +++ b/arch/x86/ia32/ia32_signal.c @@ -43,7 +43,6 @@ X86_EFLAGS_ZF | X86_EFLAGS_AF | X86_EFLAGS_PF | \ X86_EFLAGS_CF) -asmlinkage int do_signal(struct pt_regs *regs, sigset_t *oldset); void signal_fault(struct pt_regs *regs, void __user *frame, char *where); int copy_siginfo_to_user32(compat_siginfo_t __user *to, siginfo_t *from) -- cgit v1.2.2