[PATCH] eCryptfs - use page_alloc not kmalloc to get a page of memory

[Eric Sandeen <sandeen@redhat.com>]

With SLUB debugging turned on in 2.6.26, I was getting memory corruption
when testing eCryptfs.  The root cause turned out to be that eCryptfs
was doing kmalloc(PAGE_CACHE_SIZE); virt_to_page() and treating that
as a nice page-aligned chunk of memory.  But at least with SLUB debugging
on, this is not always true, and the page we get from virt_to_page does
not necessarily match the PAGE_CACHE_SIZE worth of memory we got from 
kmalloc.

My simple testcase was 2 loops doing "rm -f fileX; cp /tmp/fileX ." for
2 different multi-megabyte files.  With this change I no longer see
the corruption.

Thanks,
-Eric

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
---

Index: linux-2.6.26/fs/ecryptfs/crypto.c
===================================================================
--- linux-2.6.26.orig/fs/ecryptfs/crypto.c
+++ linux-2.6.26/fs/ecryptfs/crypto.c
@@ -474,8 +474,8 @@ int ecryptfs_encrypt_page(struct page *p
 {
 	struct inode *ecryptfs_inode;
 	struct ecryptfs_crypt_stat *crypt_stat;
-	char *enc_extent_virt = NULL;
-	struct page *enc_extent_page;
+	char *enc_extent_virt;
+	struct page *enc_extent_page = NULL;
 	loff_t extent_offset;
 	int rc = 0;
 
@@ -491,14 +491,14 @@ int ecryptfs_encrypt_page(struct page *p
 			       page->index);
 		goto out;
 	}
-	enc_extent_virt = kmalloc(PAGE_CACHE_SIZE, GFP_USER);
-	if (!enc_extent_virt) {
+	enc_extent_page = alloc_page(GFP_USER);
+	if (!enc_extent_page) {
 		rc = -ENOMEM;
 		ecryptfs_printk(KERN_ERR, "Error allocating memory for "
 				"encrypted extent\n");
 		goto out;
 	}
-	enc_extent_page = virt_to_page(enc_extent_virt);
+	enc_extent_virt = kmap(enc_extent_page);
 	for (extent_offset = 0;
 	     extent_offset < (PAGE_CACHE_SIZE / crypt_stat->extent_size);
 	     extent_offset++) {
@@ -526,7 +526,10 @@ int ecryptfs_encrypt_page(struct page *p
 		}
 	}
 out:
-	kfree(enc_extent_virt);
+	if (enc_extent_page) {
+		kunmap(enc_extent_page);
+		__free_page(enc_extent_page);
+	}
 	return rc;
 }
 
@@ -608,8 +611,8 @@ int ecryptfs_decrypt_page(struct page *p
 {
 	struct inode *ecryptfs_inode;
 	struct ecryptfs_crypt_stat *crypt_stat;
-	char *enc_extent_virt = NULL;
-	struct page *enc_extent_page;
+	char *enc_extent_virt;
+	struct page *enc_extent_page = NULL;
 	unsigned long extent_offset;
 	int rc = 0;
 
@@ -626,14 +629,14 @@ int ecryptfs_decrypt_page(struct page *p
 			       page->index);
 		goto out;
 	}
-	enc_extent_virt = kmalloc(PAGE_CACHE_SIZE, GFP_USER);
-	if (!enc_extent_virt) {
+	enc_extent_page = alloc_page(GFP_USER);
+	if (!enc_extent_page) {
 		rc = -ENOMEM;
 		ecryptfs_printk(KERN_ERR, "Error allocating memory for "
 				"encrypted extent\n");
 		goto out;
 	}
-	enc_extent_page = virt_to_page(enc_extent_virt);
+	enc_extent_virt = kmap(enc_extent_page);
 	for (extent_offset = 0;
 	     extent_offset < (PAGE_CACHE_SIZE / crypt_stat->extent_size);
 	     extent_offset++) {
@@ -661,7 +664,10 @@ int ecryptfs_decrypt_page(struct page *p
 		}
 	}
 out:
-	kfree(enc_extent_virt);
+	if (enc_extent_page) {
+		kunmap(enc_extent_page);
+		__free_page(enc_extent_page);
+	}
 	return rc;
 }