[PATCH 05/73] allocate: Harden slab allocation bounds, zeroing, and mmap checks

[Bart Van Assche <bvanassche@acm.org>]

Harden allocator bounds and statistics handling in allocate.c and
compat/mmap-blob.c:
- Zero reused freelist blocks with memset() instead of a pointer-sized
  loop in allocate().
- Check size > chunking - offset before calling blob_alloc() so blob
  header alignment overhead cannot underflow blob->left.
- Guard show_allocations() against division by zero when no allocations
  occurred.
- Check power-of-two chunk rounding and 4096-byte page alignment in
  blob_alloc() and blob_free().

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---
 allocate.c         | 22 +++++++++++-----------
 compat/mmap-blob.c |  4 ++--
 2 files changed, 13 insertions(+), 13 deletions(-)

diff --git a/allocate.c b/allocate.c
index bef85192eab1..2aca1815e5f2 100644
--- a/allocate.c
+++ b/allocate.c
@@ -33,6 +33,7 @@
 #include <stdlib.h>
 #include <stddef.h>
 #include <stdio.h>
+#include <string.h>
 
 #include "lib.h"
 #include "allocate.h"
@@ -88,10 +89,7 @@ void *allocate(struct allocator_struct *desc, unsigned int size)
 		void **p = desc->freelist;
 		retval = p;
 		desc->freelist = *p;
-		do {
-			*p = NULL;
-			p++;
-		} while ((size -= sizeof(void *)) > 0);
+		memset(retval, 0, size);
 		return retval;
 	}
 
@@ -100,17 +98,19 @@ void *allocate(struct allocator_struct *desc, unsigned int size)
 	size = (size + alignment - 1) & ~(alignment-1);
 	if (!blob || blob->left < size) {
 		unsigned int offset, chunking = desc->chunking;
-		struct allocation_blob *newblob = blob_alloc(chunking);
+		struct allocation_blob *newblob;
+
+		offset = offsetof(struct allocation_blob, data);
+		offset = (offset + alignment - 1) & ~(alignment-1);
+		if (size > chunking - offset)
+			die("alloc too big");
+		newblob = blob_alloc(chunking);
 		if (!newblob)
 			die("out of memory");
-		if (size > chunking)
-			die("alloc too big");
 		desc->total_bytes += chunking;
 		newblob->next = blob;
 		blob = newblob;
 		desc->blobs = newblob;
-		offset = offsetof(struct allocation_blob, data);
-		offset = (offset + alignment - 1) & ~(alignment-1);
 		blob->left = chunking - offset;
 		blob->offset = offset - offsetof(struct allocation_blob, data);
 	}
@@ -125,8 +125,8 @@ void show_allocations(struct allocator_struct *x)
 	fprintf(stderr, "%s: %d allocations, %lu bytes (%lu total bytes, "
 			"%6.2f%% usage, %6.2f average size)\n",
 		x->name, x->allocations, x->useful_bytes, x->total_bytes,
-		100 * (double) x->useful_bytes / x->total_bytes,
-		(double) x->useful_bytes / x->allocations);
+		100 * (double) x->useful_bytes / (x->total_bytes ?: 1),
+		(double) x->useful_bytes / (x->allocations ?: 1));
 }
 
 void get_allocator_stats(struct allocator_struct *x, struct allocator_stats *s)
diff --git a/compat/mmap-blob.c b/compat/mmap-blob.c
index 1cab4dead96d..91edeb9bc8d8 100644
--- a/compat/mmap-blob.c
+++ b/compat/mmap-blob.c
@@ -17,7 +17,7 @@ void *blob_alloc(unsigned long size)
 {
 	void *ptr;
 
-	if (size & ~CHUNK)
+	if (!size || (size & (CHUNK - 1)))
 		die("internal error: bad allocation size (%lu bytes)", size);
 	ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 	if (ptr == MAP_FAILED)
@@ -27,7 +27,7 @@ void *blob_alloc(unsigned long size)
 
 void blob_free(void *addr, unsigned long size)
 {
-	if (!size || (size & ~CHUNK) || ((unsigned long) addr & 512))
+	if (!size || (size & (CHUNK - 1)) || ((unsigned long) addr & 4095))
 		die("internal error: bad blob free (%lu bytes at %p)", size, addr);
 #ifndef DEBUG
 	munmap(addr, size);