cifs: fix strcat buffer overflow and reduce raciness in smb21_set_opl…

…ock_level() Change strcat to strncpy in the "None" case to fix a buffer overflow when cinode->oplock is reset to 0 by another thread accessing the same cinode. It is never valid to append "None" to any other message. Consolidate multiple writes to cinode->oplock to reduce raciness. Signed-off-by: Christoph Probst <[email protected]> Reviewed-by: Pavel Shilovsky <[email protected]> Signed-off-by: Steve French <[email protected]> CC: Stable <[email protected]>
berg · May 8, 2019 · 6a54b2e · 6a54b2e
1 parent 26ea888
commit 6a54b2e
Showing 1 changed file with 8 additions and 6 deletions.
diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
@@ -2974,26 +2974,28 @@ smb21_set_oplock_level(struct cifsInodeInfo *cinode, __u32 oplock,
 		       unsigned int epoch, bool *purge_cache)
 {
 	char message[5] = {0};
+	unsigned int new_oplock = 0;
 
 	oplock &= 0xFF;
 	if (oplock == SMB2_OPLOCK_LEVEL_NOCHANGE)
 		return;
 
-	cinode->oplock = 0;
 	if (oplock & SMB2_LEASE_READ_CACHING_HE) {
-		cinode->oplock |= CIFS_CACHE_READ_FLG;
+		new_oplock |= CIFS_CACHE_READ_FLG;
 		strcat(message, "R");
 	}
 	if (oplock & SMB2_LEASE_HANDLE_CACHING_HE) {
-		cinode->oplock |= CIFS_CACHE_HANDLE_FLG;
+		new_oplock |= CIFS_CACHE_HANDLE_FLG;
 		strcat(message, "H");
 	}
 	if (oplock & SMB2_LEASE_WRITE_CACHING_HE) {
-		cinode->oplock |= CIFS_CACHE_WRITE_FLG;
+		new_oplock |= CIFS_CACHE_WRITE_FLG;
 		strcat(message, "W");
 	}
-	if (!cinode->oplock)
-		strcat(message, "None");
+	if (!new_oplock)
+		strncpy(message, "None", sizeof(message));
+
+	cinode->oplock = new_oplock;
 	cifs_dbg(FYI, "%s Lease granted on inode %p\n", message,
 		 &cinode->vfs_inode);
 }