Implement AT_SECURE properly.

AT_SECURE auxv entry has been added to the Linux 2.5 kernel to pass a
boolean flag indicating whether secure mode should be enabled. 1 means
that the program has changes its credentials during the execution.
Being exported AT_SECURE used by glibc issetugid() call.

Submitted by:	imp, dchagin
Security:	FreeBSD-SA-16:10.linux
Security:	CVE-2016-1883

3 files changed, 9 insertions, 3 deletions

diff --git a/sys/amd64/linux/linux_sysvec.c b/sys/amd64/linux/linux_sysvec.c
index d49ca79..0bdcba0 100644
--- a/sys/amd64/linux/linux_sysvec.c
+++ b/sys/amd64/linux/linux_sysvec.c
@@ -271,6 +271,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	Elf_Addr *pos;
 	struct ps_strings *arginfo;
 	struct proc *p;
+	int issetugid;
 
 	p = imgp->proc;
 	arginfo = (struct ps_strings *)p->p_sysent->sv_psstrings;
@@ -281,6 +282,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	args = (Elf64_Auxargs *)imgp->auxargs;
 	pos = base + (imgp->args->argc + imgp->args->envc + 2);
 
+	issetugid = p->p_flag & P_SUGID ? 1 : 0;
 	AUXARGS_ENTRY(pos, LINUX_AT_SYSINFO_EHDR,
 	    imgp->proc->p_sysent->sv_shared_page_base);
 	AUXARGS_ENTRY(pos, LINUX_AT_HWCAP, cpu_feature);
@@ -296,7 +298,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	AUXARGS_ENTRY(pos, AT_EUID, imgp->proc->p_ucred->cr_svuid);
 	AUXARGS_ENTRY(pos, AT_GID, imgp->proc->p_ucred->cr_rgid);
 	AUXARGS_ENTRY(pos, AT_EGID, imgp->proc->p_ucred->cr_svgid);
-	AUXARGS_ENTRY(pos, LINUX_AT_SECURE, 0);
+	AUXARGS_ENTRY(pos, LINUX_AT_SECURE, issetugid);
 	AUXARGS_ENTRY(pos, LINUX_AT_PLATFORM, PTROUT(linux_platform));
 	AUXARGS_ENTRY(pos, LINUX_AT_RANDOM, imgp->canary);
 	if (imgp->execpathp != 0)
diff --git a/sys/amd64/linux32/linux32_sysvec.c b/sys/amd64/linux32/linux32_sysvec.c
index 7d3615e..f89b8fa 100644
--- a/sys/amd64/linux32/linux32_sysvec.c
+++ b/sys/amd64/linux32/linux32_sysvec.c
@@ -230,6 +230,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	Elf32_Addr *base;
 	Elf32_Addr *pos;
 	struct linux32_ps_strings *arginfo;
+	int issetugid;
 
 	arginfo = (struct linux32_ps_strings *)LINUX32_PS_STRINGS;
 
@@ -239,6 +240,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	args = (Elf32_Auxargs *)imgp->auxargs;
 	pos = base + (imgp->args->argc + imgp->args->envc + 2);
 
+	issetugid = imgp->proc->p_flag & P_SUGID ? 1 : 0;
 	AUXARGS_ENTRY_32(pos, LINUX_AT_SYSINFO_EHDR,
 	    imgp->proc->p_sysent->sv_shared_page_base);
 	AUXARGS_ENTRY_32(pos, LINUX_AT_SYSINFO, linux32_vsyscall);
@@ -261,7 +263,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	AUXARGS_ENTRY_32(pos, AT_FLAGS, args->flags);
 	AUXARGS_ENTRY_32(pos, AT_ENTRY, args->entry);
 	AUXARGS_ENTRY_32(pos, AT_BASE, args->base);
-	AUXARGS_ENTRY_32(pos, LINUX_AT_SECURE, 0);
+	AUXARGS_ENTRY_32(pos, LINUX_AT_SECURE, issetugid);
 	AUXARGS_ENTRY_32(pos, AT_UID, imgp->proc->p_ucred->cr_ruid);
 	AUXARGS_ENTRY_32(pos, AT_EUID, imgp->proc->p_ucred->cr_svuid);
 	AUXARGS_ENTRY_32(pos, AT_GID, imgp->proc->p_ucred->cr_rgid);
diff --git a/sys/i386/linux/linux_sysvec.c b/sys/i386/linux/linux_sysvec.c
index cc5fcaa..c4a5ee5 100644
--- a/sys/i386/linux/linux_sysvec.c
+++ b/sys/i386/linux/linux_sysvec.c
@@ -238,11 +238,13 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	Elf32_Addr *uplatform;
 	struct ps_strings *arginfo;
 	register_t *pos;
+	int issetugid;
 
 	KASSERT(curthread->td_proc == imgp->proc,
 	    ("unsafe elf_linux_fixup(), should be curproc"));
 
 	p = imgp->proc;
+	issetugid = imgp->proc->p_flag & P_SUGID ? 1 : 0;
 	arginfo = (struct ps_strings *)p->p_sysent->sv_psstrings;
 	uplatform = (Elf32_Addr *)((caddr_t)arginfo - linux_szplatform);
 	args = (Elf32_Auxargs *)imgp->auxargs;
@@ -270,7 +272,7 @@ elf_linux_fixup(register_t **stack_base, struct image_params *imgp)
 	AUXARGS_ENTRY(pos, AT_FLAGS, args->flags);
 	AUXARGS_ENTRY(pos, AT_ENTRY, args->entry);
 	AUXARGS_ENTRY(pos, AT_BASE, args->base);
-	AUXARGS_ENTRY(pos, LINUX_AT_SECURE, 0);
+	AUXARGS_ENTRY(pos, LINUX_AT_SECURE, issetugid);
 	AUXARGS_ENTRY(pos, AT_UID, imgp->proc->p_ucred->cr_ruid);
 	AUXARGS_ENTRY(pos, AT_EUID, imgp->proc->p_ucred->cr_svuid);
 	AUXARGS_ENTRY(pos, AT_GID, imgp->proc->p_ucred->cr_rgid);