exec: pass stack rlimit into mm layout functions

Patch series "exec: Pin stack limit during exec". Attempts to solve problems with the stack limit changing during exec continue to be frustrated[1][2]. In addition to the specific issues around the Stack Clash family of flaws, Andy Lutomirski pointed out[3] other places during exec where the stack limit is used and is assumed to be unchanging. Given the many places it gets used and the fact that it can be manipulated/raced via setrlimit() and prlimit(), I think the only way to handle this is to move away from the "current" view of the stack limit and instead attach it to the bprm, and plumb this down into the functions that need to know the stack limits. This series implements the approach. [1] 04e35f4 ("exec: avoid RLIMIT_STACK races with prlimit()") [2] 779f4e1 ("Revert "exec: avoid RLIMIT_STACK races with prlimit()"") [3] to [email protected], "Subject: existing rlimit races?" This patch (of 3): Since it is possible that the stack rlimit can change externally during exec (either via another thread calling setrlimit() or another process calling prlimit()), provide a way to pass the rlimit down into the per-architecture mm layout functions so that the rlimit can stay in the bprm structure instead of sitting in the signal structure until exec is finalized. Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Kees Cook <[email protected]> Cc: Michal Hocko <[email protected]> Cc: Ben Hutchings <[email protected]> Cc: Willy Tarreau <[email protected]> Cc: Hugh Dickins <[email protected]> Cc: Oleg Nesterov <[email protected]> Cc: "Jason A. Donenfeld" <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Laura Abbott <[email protected]> Cc: Greg KH <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Ben Hutchings <[email protected]> Cc: Brad Spengler <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
berg · Apr 11, 2018 · 8f2af15 · 8f2af15
1 parent d64d01a
commit 8f2af15
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Showing 11 changed files with 81 additions and 58 deletions.
diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
@@ -21,20 +21,20 @@
 #define MIN_GAP (128*1024*1024UL)
 #define MAX_GAP ((TASK_SIZE)/6*5)
 
-static int mmap_is_legacy(void)
+static int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
 
-	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 		return 1;
 
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_base(unsigned long rnd)
+static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 
 	if (gap < MIN_GAP)
 		gap = MIN_GAP;
@@ -180,18 +180,18 @@ unsigned long arch_mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
 		random_factor = arch_mmap_rnd();
 
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }

diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
@@ -38,12 +38,12 @@
 #define MIN_GAP (SZ_128M)
 #define MAX_GAP	(STACK_TOP/6*5)
 
-static int mmap_is_legacy(void)
+static int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
 
-	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 		return 1;
 
 	return sysctl_legacy_va_layout;
@@ -62,9 +62,9 @@ unsigned long arch_mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
-static unsigned long mmap_base(unsigned long rnd)
+static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 	unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
 
 	/* Values close to RLIM_INFINITY can overflow. */
@@ -83,7 +83,7 @@ static unsigned long mmap_base(unsigned long rnd)
  * This function, called very early during the creation of a new process VM
  * image, sets up which VM layout function to use:
  */
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
 
@@ -94,11 +94,11 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 	 * Fall back to the standard layout if the personality bit is set, or
 	 * if the expected stack growth is unlimited:
 	 */
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }

diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
@@ -24,20 +24,20 @@ EXPORT_SYMBOL(shm_align_mask);
 #define MIN_GAP (128*1024*1024UL)
 #define MAX_GAP ((TASK_SIZE)/6*5)
 
-static int mmap_is_legacy(void)
+static int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
 
-	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 		return 1;
 
 	return sysctl_legacy_va_layout;
 }
 
-static unsigned long mmap_base(unsigned long rnd)
+static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 
 	if (gap < MIN_GAP)
 		gap = MIN_GAP;
@@ -158,18 +158,18 @@ unsigned long arch_mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
 		random_factor = arch_mmap_rnd();
 
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }

diff --git a/arch/parisc/kernel/sys_parisc.c b/arch/parisc/kernel/sys_parisc.c
@@ -70,12 +70,18 @@ static inline unsigned long COLOR_ALIGN(unsigned long addr,
  * Top of mmap area (just below the process stack).
  */
 
-static unsigned long mmap_upper_limit(void)
+/*
+ * When called from arch_get_unmapped_area(), rlim_stack will be NULL,
+ * indicating that "current" should be used instead of a passed-in
+ * value from the exec bprm as done with arch_pick_mmap_layout().
+ */
+static unsigned long mmap_upper_limit(struct rlimit *rlim_stack)
 {
 	unsigned long stack_base;
 
 	/* Limit stack size - see setup_arg_pages() in fs/exec.c */
-	stack_base = rlimit_max(RLIMIT_STACK);
+	stack_base = rlim_stack ? rlim_stack->rlim_max
+				: rlimit_max(RLIMIT_STACK);
 	if (stack_base > STACK_SIZE_MAX)
 		stack_base = STACK_SIZE_MAX;
 
@@ -127,7 +133,7 @@ unsigned long arch_get_unmapped_area(struct file *filp, unsigned long addr,
 	info.flags = 0;
 	info.length = len;
 	info.low_limit = mm->mmap_legacy_base;
-	info.high_limit = mmap_upper_limit();
+	info.high_limit = mmap_upper_limit(NULL);
 	info.align_mask = last_mmap ? (PAGE_MASK & (SHM_COLOUR - 1)) : 0;
 	info.align_offset = shared_align_offset(last_mmap, pgoff);
 	addr = vm_unmapped_area(&info);
@@ -250,10 +256,10 @@ static unsigned long mmap_legacy_base(void)
  * This function, called very early during the creation of a new
  * process VM image, sets up which VM layout function to use:
  */
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	mm->mmap_legacy_base = mmap_legacy_base();
-	mm->mmap_base = mmap_upper_limit();
+	mm->mmap_base = mmap_upper_limit(rlim_stack);
 
 	if (mmap_is_legacy()) {
 		mm->mmap_base = mm->mmap_legacy_base;

diff --git a/arch/powerpc/mm/mmap.c b/arch/powerpc/mm/mmap.c
@@ -39,12 +39,12 @@
 #define MIN_GAP (128*1024*1024)
 #define MAX_GAP (TASK_SIZE/6*5)
 
-static inline int mmap_is_legacy(void)
+static inline int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
 
-	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 		return 1;
 
 	return sysctl_legacy_va_layout;
@@ -76,9 +76,10 @@ static inline unsigned long stack_maxrandom_size(void)
 		return (1<<30);
 }
 
-static inline unsigned long mmap_base(unsigned long rnd)
+static inline unsigned long mmap_base(unsigned long rnd,
+				      struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 	unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
 
 	/* Values close to RLIM_INFINITY can overflow. */
@@ -196,43 +197,46 @@ radix__arch_get_unmapped_area_topdown(struct file *filp,
 }
 
 static void radix__arch_pick_mmap_layout(struct mm_struct *mm,
-					unsigned long random_factor)
+					unsigned long random_factor,
+					struct rlimit *rlim_stack)
 {
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = TASK_UNMAPPED_BASE;
 		mm->get_unmapped_area = radix__arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = radix__arch_get_unmapped_area_topdown;
 	}
 }
 #else
 /* dummy */
 extern void radix__arch_pick_mmap_layout(struct mm_struct *mm,
-					unsigned long random_factor);
+					unsigned long random_factor,
+					struct rlimit *rlim_stack);
 #endif
 /*
  * This function, called very early during the creation of a new
  * process VM image, sets up which VM layout function to use:
  */
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
 
 	if (current->flags & PF_RANDOMIZE)
 		random_factor = arch_mmap_rnd();
 
 	if (radix_enabled())
-		return radix__arch_pick_mmap_layout(mm, random_factor);
+		return radix__arch_pick_mmap_layout(mm, random_factor,
+						    rlim_stack);
 	/*
 	 * Fall back to the standard layout if the personality
 	 * bit is set, or if the expected stack growth is unlimited:
 	 */
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = TASK_UNMAPPED_BASE;
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
@@ -37,11 +37,11 @@ static unsigned long stack_maxrandom_size(void)
 #define MIN_GAP (32*1024*1024)
 #define MAX_GAP (STACK_TOP/6*5)
 
-static inline int mmap_is_legacy(void)
+static inline int mmap_is_legacy(struct rlimit *rlim_stack)
 {
 	if (current->personality & ADDR_COMPAT_LAYOUT)
 		return 1;
-	if (rlimit(RLIMIT_STACK) == RLIM_INFINITY)
+	if (rlim_stack->rlim_cur == RLIM_INFINITY)
 		return 1;
 	return sysctl_legacy_va_layout;
 }
@@ -56,9 +56,10 @@ static unsigned long mmap_base_legacy(unsigned long rnd)
 	return TASK_UNMAPPED_BASE + rnd;
 }
 
-static inline unsigned long mmap_base(unsigned long rnd)
+static inline unsigned long mmap_base(unsigned long rnd,
+				      struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 
 	if (gap < MIN_GAP)
 		gap = MIN_GAP;
@@ -184,7 +185,7 @@ arch_get_unmapped_area_topdown(struct file *filp, const unsigned long addr0,
  * This function, called very early during the creation of a new
  * process VM image, sets up which VM layout function to use:
  */
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = 0UL;
 
@@ -195,11 +196,11 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 	 * Fall back to the standard layout if the personality
 	 * bit is set, or if the expected stack growth is unlimited:
 	 */
-	if (mmap_is_legacy()) {
+	if (mmap_is_legacy(rlim_stack)) {
 		mm->mmap_base = mmap_base_legacy(random_factor);
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	} else {
-		mm->mmap_base = mmap_base(random_factor);
+		mm->mmap_base = mmap_base(random_factor, rlim_stack);
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 	}
 }
diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
@@ -276,7 +276,7 @@ static unsigned long mmap_rnd(void)
 	return rnd << PAGE_SHIFT;
 }
 
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	unsigned long random_factor = mmap_rnd();
 	unsigned long gap;
@@ -285,7 +285,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 	 * Fall back to the standard layout if the personality
 	 * bit is set, or if the expected stack growth is unlimited:
 	 */
-	gap = rlimit(RLIMIT_STACK);
+	gap = rlim_stack->rlim_cur;
 	if (!test_thread_flag(TIF_32BIT) ||
 	    (current->personality & ADDR_COMPAT_LAYOUT) ||
 	    gap == RLIM_INFINITY ||

diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
@@ -90,9 +90,10 @@ unsigned long arch_mmap_rnd(void)
 	return arch_rnd(mmap_is_ia32() ? mmap32_rnd_bits : mmap64_rnd_bits);
 }
 
-static unsigned long mmap_base(unsigned long rnd, unsigned long task_size)
+static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
+			       struct rlimit *rlim_stack)
 {
-	unsigned long gap = rlimit(RLIMIT_STACK);
+	unsigned long gap = rlim_stack->rlim_cur;
 	unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
 	unsigned long gap_min, gap_max;
 
@@ -126,24 +127,26 @@ static unsigned long mmap_legacy_base(unsigned long rnd,
  * process VM image, sets up which VM layout function to use:
  */
 static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
-		unsigned long random_factor, unsigned long task_size)
+		unsigned long random_factor, unsigned long task_size,
+		struct rlimit *rlim_stack)
 {
 	*legacy_base = mmap_legacy_base(random_factor, task_size);
 	if (mmap_is_legacy())
 		*base = *legacy_base;
 	else
-		*base = mmap_base(random_factor, task_size);
+		*base = mmap_base(random_factor, task_size, rlim_stack);
 }
 
-void arch_pick_mmap_layout(struct mm_struct *mm)
+void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 {
 	if (mmap_is_legacy())
 		mm->get_unmapped_area = arch_get_unmapped_area;
 	else
 		mm->get_unmapped_area = arch_get_unmapped_area_topdown;
 
 	arch_pick_mmap_base(&mm->mmap_base, &mm->mmap_legacy_base,
-			arch_rnd(mmap64_rnd_bits), task_size_64bit(0));
+			arch_rnd(mmap64_rnd_bits), task_size_64bit(0),
+			rlim_stack);
 
 #ifdef CONFIG_HAVE_ARCH_COMPAT_MMAP_BASES
 	/*
@@ -153,7 +156,8 @@ void arch_pick_mmap_layout(struct mm_struct *mm)
 	 * mmap_base, the compat syscall uses mmap_compat_base.
 	 */
 	arch_pick_mmap_base(&mm->mmap_compat_base, &mm->mmap_compat_legacy_base,
-			arch_rnd(mmap32_rnd_bits), task_size_32bit());
+			arch_rnd(mmap32_rnd_bits), task_size_32bit(),
+			rlim_stack);
 #endif
 }