[PATCH v2 1/3] ecryptfs: pass packet set buffer size to parser

[Yichong Chen]

ecryptfs_parse_packet_set() receives a pointer into the file header, but
it calculates the remaining packet buffer size from PAGE_SIZE - 8.  For
version 1 headers the packet set starts later in the header, so this can
overstate the available buffer.

Pass the actual packet set buffer length from the caller and calculate
per-packet limits from the remaining bytes in that buffer.  Recompute the
remaining length after consuming a tag 3 packet before parsing the
following tag 11 packet.

Fixes: 237fead61998 ("[PATCH] ecryptfs: fs/Makefile and fs/Kconfig")
Signed-off-by: Yichong Chen <chenyichong@xxxxxxxxxxxxx>
---
 fs/ecryptfs/crypto.c          |  2 +-
 fs/ecryptfs/ecryptfs_kernel.h |  3 ++-
 fs/ecryptfs/keystore.c        | 23 ++++++++++++++++++++---
 3 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index 74b02b5..e67119b 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1197,7 +1197,7 @@ static int ecryptfs_read_headers_virt(char *page_virt,
 	} else
 		set_default_header_data(crypt_stat);
 	rc = ecryptfs_parse_packet_set(crypt_stat, (page_virt + offset),
-				       ecryptfs_dentry);
+				       PAGE_SIZE - offset, ecryptfs_dentry);
 out:
 	return rc;
 }
diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index f4f56a9..7d2488a 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -580,7 +580,8 @@ int ecryptfs_generate_key_packet_set(char *dest_base,
 				     size_t *len, size_t max);
 int
 ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
-			  unsigned char *src, struct dentry *ecryptfs_dentry);
+			  unsigned char *src, size_t src_size,
+			  struct dentry *ecryptfs_dentry);
 int ecryptfs_truncate(struct dentry *dentry, loff_t new_length);
 ssize_t
 ecryptfs_getxattr_lower(struct dentry *lower_dentry, struct inode *lower_inode,
diff --git a/fs/ecryptfs/keystore.c b/fs/ecryptfs/keystore.c
index ebebc95..90c2b80 100644
--- a/fs/ecryptfs/keystore.c
+++ b/fs/ecryptfs/keystore.c
@@ -1704,6 +1704,7 @@ out:
  * ecryptfs_parse_packet_set
  * @crypt_stat: The cryptographic context
  * @src: Virtual address of region of memory containing the packets
+ * @src_size: Size of the packet set buffer
  * @ecryptfs_dentry: The eCryptfs dentry associated with the packet set
  *
  * Get crypt_stat to have the file's session key if the requisite key
@@ -1714,7 +1715,7 @@ out:
  * conditions.
  */
 int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
-			      unsigned char *src,
+			      unsigned char *src, size_t src_size,
 			      struct dentry *ecryptfs_dentry)
 {
 	size_t i = 0;
@@ -1736,7 +1737,11 @@ int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
 	 * added the our &auth_tok_list */
 	next_packet_is_auth_tok_packet = 1;
 	while (next_packet_is_auth_tok_packet) {
-		size_t max_packet_size = ((PAGE_SIZE - 8) - i);
+		size_t max_packet_size;
+
+		if (i >= src_size)
+			break;
+		max_packet_size = src_size - i;
 
 		switch (src[i]) {
 		case ECRYPTFS_TAG_3_PACKET_TYPE:
@@ -1751,12 +1756,16 @@ int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
 				goto out_wipe_list;
 			}
 			i += packet_size;
+			if (i > src_size) {
+				rc = -EIO;
+				goto out_wipe_list;
+			}
 			rc = parse_tag_11_packet((unsigned char *)&src[i],
 						 sig_tmp_space,
 						 ECRYPTFS_SIG_SIZE,
 						 &tag_11_contents_size,
 						 &tag_11_packet_size,
-						 max_packet_size);
+						 src_size - i);
 			if (rc) {
 				ecryptfs_printk(KERN_ERR, "No valid "
 						"(ecryptfs-specific) literal "
@@ -1768,6 +1777,10 @@ int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
 				goto out_wipe_list;
 			}
 			i += tag_11_packet_size;
+			if (i > src_size) {
+				rc = -EIO;
+				goto out_wipe_list;
+			}
 			if (ECRYPTFS_SIG_SIZE != tag_11_contents_size) {
 				ecryptfs_printk(KERN_ERR, "Expected "
 						"signature of size [%d]; "
@@ -1793,6 +1806,10 @@ int ecryptfs_parse_packet_set(struct ecryptfs_crypt_stat *crypt_stat,
 				goto out_wipe_list;
 			}
 			i += packet_size;
+			if (i > src_size) {
+				rc = -EIO;
+				goto out_wipe_list;
+			}
 			crypt_stat->flags |= ECRYPTFS_ENCRYPTED;
 			break;
 		case ECRYPTFS_TAG_11_PACKET_TYPE:
-- 
2.51.0