[PATCH 4.19 251/361] ima: open a new file instance if no read permissions

[Greg Kroah-Hartman]

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Goldwyn Rodrigues <rgoldwyn@xxxxxxx>

commit a408e4a86b36bf98ad15b9ada531cf0e5118ac67 upstream.

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 in read mode
if original file cannot be read, read and calculate the hash.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx (linux-4.19)
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 security/integrity/ima/ima_crypto.c |   54 ++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 20 deletions(-)

--- 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(struc
 {
 	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(struc
 					  &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(struc
 	/* 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
 {
 	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
 	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
 		if (rc)
 			break;
 	}
-	if (read)
-		file->f_mode &= ~FMODE_READ;
 	kfree(rbuf);
 out:
 	if (!rc)
@@ -420,6 +406,8 @@ int ima_calc_file_hash(struct file *file
 {
 	loff_t i_size;
 	int rc;
+	struct file *f = file;
+	bool new_file_instance = false, modified_flags = false;
 
 	/*
 	 * For consistency, fail file's opened with the O_DIRECT flag on
@@ -431,15 +419,41 @@ int ima_calc_file_hash(struct file *file
 		return -EINVAL;
 	}
 
-	i_size = i_size_read(file_inode(file));
+	/* Open a new file instance in O_RDONLY if we cannot read */
+	if (!(file->f_mode & FMODE_READ)) {
+		int flags = file->f_flags & ~(O_WRONLY | O_APPEND |
+				O_TRUNC | O_CREAT | O_NOCTTY | O_EXCL);
+		flags |= O_RDONLY;
+		f = dentry_open(&file->f_path, flags, file->f_cred);
+		if (IS_ERR(f)) {
+			/*
+			 * Cannot open the file again, lets modify f_flags
+			 * of original and continue
+			 */
+			pr_info_ratelimited("Unable to reopen file for reading.\n");
+			f = file;
+			f->f_flags |= FMODE_READ;
+			modified_flags = true;
+		} else {
+			new_file_instance = true;
+		}
+	}
+
+	i_size = i_size_read(file_inode(f));
 
 	if (ima_ahash_minsize && i_size >= ima_ahash_minsize) {
-		rc = ima_calc_file_ahash(file, hash);
+		rc = ima_calc_file_ahash(f, hash);
 		if (!rc)
-			return 0;
+			goto out;
 	}
 
-	return ima_calc_file_shash(file, hash);
+	rc = ima_calc_file_shash(f, hash);
+out:
+	if (new_file_instance)
+		fput(f);
+	else if (modified_flags)
+		f->f_flags &= ~FMODE_READ;
+	return rc;
 }
 
 /*