[PATCH 2/2] ima: allocate user-space like memory for direct-io

[Dmitry Kasatkin]

For files opened with O_DIRECT flag, file I/O is done directly to/from
user-space pages. kmalloc or vmalloc allocated memory is not suitable
for direct IO and set_fs(get_ds()) trick does not work there.

This patch uses vm_mmap() call to allocated annonymous user-space like
memory from the kernel.

Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
---
 security/integrity/ima/ima_crypto.c | 44 ++++++++++++++++++++++++++++++-------
 1 file changed, 36 insertions(+), 8 deletions(-)

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index de5b974..59efc0a 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -21,6 +21,7 @@
 #include <linux/scatterlist.h>
 #include <linux/err.h>
 #include <linux/slab.h>
+#include <linux/mman.h>
 #include <crypto/hash.h>
 #include <crypto/hash_info.h>
 #include "ima.h"
@@ -36,7 +37,7 @@ static struct crypto_shash *ima_shash_tfm;
  *
  */
 static int ima_kernel_read(struct file *file, loff_t offset,
-			   char *addr, unsigned long count)
+			   char *addr, unsigned long count, bool kmem)
 {
 	mm_segment_t old_fs;
 	char __user *buf = addr;
@@ -47,13 +48,16 @@ static int ima_kernel_read(struct file *file, loff_t offset,
 	if (!file->f_op->read && !file->f_op->aio_read)
 		return -EINVAL;
 
-	old_fs = get_fs();
-	set_fs(get_ds());
+	if (kmem) {
+		old_fs = get_fs();
+		set_fs(get_ds());
+	}
 	if (file->f_op->read)
 		ret = file->f_op->read(file, buf, count, &offset);
 	else
 		ret = do_sync_read(file, buf, count, &offset);
-	set_fs(old_fs);
+	if (kmem)
+		set_fs(old_fs);
 	return ret;
 }
 
@@ -102,6 +106,7 @@ static int ima_calc_file_hash_tfm(struct file *file,
 {
 	loff_t i_size, offset = 0;
 	char *rbuf;
+	unsigned long addr = 0;
 	int rc, read = 0;
 	struct {
 		struct shash_desc shash;
@@ -122,9 +127,22 @@ static int ima_calc_file_hash_tfm(struct file *file,
 	if (i_size == 0)
 		goto out;
 
-	rbuf = kzalloc(PAGE_SIZE, GFP_KERNEL);
-	if (!rbuf)
-		return -ENOMEM;
+	if (file->f_flags & O_DIRECT) {
+		/* direct-io code writes to user-space buffers
+		 * set_fs(get_ds()) trick does not work there
+		 */
+		addr = vm_mmap(NULL, 0, PAGE_SIZE,
+				PROT_READ | PROT_WRITE,
+				MAP_PRIVATE | MAP_ANONYMOUS, 0);
+		if (IS_ERR_VALUE(addr))
+			return addr;
+	}
+
+	rbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (!rbuf) {
+		rc = -ENOMEM;
+		goto nomem;
+	}
 
 	if (!(file->f_mode & FMODE_READ)) {
 		file->f_mode |= FMODE_READ;
@@ -134,7 +152,9 @@ static int ima_calc_file_hash_tfm(struct file *file,
 	while (offset < i_size) {
 		int rbuf_len;
 
-		rbuf_len = ima_kernel_read(file, offset, rbuf, PAGE_SIZE);
+		rbuf_len = ima_kernel_read(file, offset,
+					   addr ? (char *)addr : rbuf,
+					   PAGE_SIZE, !addr);
 		if (rbuf_len < 0) {
 			rc = rbuf_len;
 			break;
@@ -143,6 +163,11 @@ static int ima_calc_file_hash_tfm(struct file *file,
 			break;
 		offset += rbuf_len;
 
+		if (addr && __copy_from_user(rbuf, (void __user *)addr,
+					     rbuf_len)) {
+			rc = -EFAULT;
+			break;
+		}
 		rc = crypto_shash_update(&desc.shash, rbuf, rbuf_len);
 		if (rc)
 			break;
@@ -150,6 +175,9 @@ static int ima_calc_file_hash_tfm(struct file *file,
 	if (read)
 		file->f_mode &= ~FMODE_READ;
 	kfree(rbuf);
+nomem:
+	if (addr)
+		vm_munmap(addr, PAGE_SIZE);
 out:
 	if (!rc)
 		rc = crypto_shash_final(&desc.shash, hash->digest);
-- 
1.9.1

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