[PATCH] Open a new file instance if no read permissions on files

[Goldwyn Rodrigues <rgoldwyn@xxxxxxx>]

Open a new file instance as opposed to changing file->f_mode when
the file is not readable.

This is done to accomodate overlayfs stacked file operations change. The
real struct file is hidden behind the overlays struct file. So, any
file->f_mode manipulations are not reflected on the real struct file.
Open the file again, read andcalculate the hash.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 7e7e7e7c250a..3848cf208792 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -210,7 +210,7 @@ static int ima_calc_file_hash_atfm(struct file *file,
 {
 	loff_t i_size, offset;
 	char *rbuf[2] = { NULL, };
-	int rc, read = 0, rbuf_len, active = 0, ahash_rc = 0;
+	int rc, rbuf_len, active = 0, ahash_rc = 0;
 	struct ahash_request *req;
 	struct scatterlist sg[1];
 	struct crypto_wait wait;
@@ -257,11 +257,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
 					  &rbuf_size[1], 0);
 	}
 
-	if (!(file->f_mode & FMODE_READ)) {
-		file->f_mode |= FMODE_READ;
-		read = 1;
-	}
-
 	for (offset = 0; offset < i_size; offset += rbuf_len) {
 		if (!rbuf[1] && offset) {
 			/* Not using two buffers, and it is not the first
@@ -300,8 +295,6 @@ static int ima_calc_file_hash_atfm(struct file *file,
 	/* wait for the last update request to complete */
 	rc = ahash_wait(ahash_rc, &wait);
 out3:
-	if (read)
-		file->f_mode &= ~FMODE_READ;
 	ima_free_pages(rbuf[0], rbuf_size[0]);
 	ima_free_pages(rbuf[1], rbuf_size[1]);
 out2:
@@ -336,7 +329,7 @@ static int ima_calc_file_hash_tfm(struct file *file,
 {
 	loff_t i_size, offset = 0;
 	char *rbuf;
-	int rc, read = 0;
+	int rc;
 	SHASH_DESC_ON_STACK(shash, tfm);
 
 	shash->tfm = tfm;
@@ -357,11 +350,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
 	if (!rbuf)
 		return -ENOMEM;
 
-	if (!(file->f_mode & FMODE_READ)) {
-		file->f_mode |= FMODE_READ;
-		read = 1;
-	}
-
 	while (offset < i_size) {
 		int rbuf_len;
 
@@ -378,8 +366,6 @@ static int ima_calc_file_hash_tfm(struct file *file,
 		if (rc)
 			break;
 	}
-	if (read)
-		file->f_mode &= ~FMODE_READ;
 	kfree(rbuf);
 out:
 	if (!rc)
@@ -419,7 +405,7 @@ static int ima_calc_file_shash(struct file *file, struct ima_digest_data *hash)
 int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 {
 	loff_t i_size;
-	int rc;
+	int read = 0, rc;
 
 	/*
 	 * For consistency, fail file's opened with the O_DIRECT flag on
@@ -431,15 +417,29 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
 		return -EINVAL;
 	}
 
+	if (!(file->f_mode & FMODE_READ)) {
+		struct file *f;
+		int flags = file->f_flags & ~(O_WRONLY | O_APPEND | O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
+		f = dentry_open(&file->f_path, flags, file->f_cred);
+		if (IS_ERR(f))
+			return PTR_ERR(f);
+		read = 1;
+		file = f;
+	}
+
 	i_size = i_size_read(file_inode(file));
 
 	if (ima_ahash_minsize && i_size >= ima_ahash_minsize) {
 		rc = ima_calc_file_ahash(file, hash);
 		if (!rc)
-			return 0;
+			goto out;
 	}
 
-	return ima_calc_file_shash(file, hash);
+	rc = ima_calc_file_shash(file, hash);
+out:
+	if (read)
+		fput(file);
+	return rc;
 }
 
 /*

-- 
Goldwyn