linux-kernel - [PATCH v2] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <1557242200-26194-1-git-send-email-kernel@probst.it>
Date:   Tue,  7 May 2019 17:16:40 +0200
From:   Christoph Probst <kernel@...bst.it>
To:     linux-cifs@...r.kernel.org
Cc:     Steve French <sfrench@...ba.org>, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org, Christoph Probst <kernel@...bst.it>
Subject: [PATCH v2] cifs: fix strcat buffer overflow and reduce raciness in smb21_set_oplock_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 <kernel@...bst.it>
---
 fs/cifs/smb2ops.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/fs/cifs/smb2ops.c b/fs/cifs/smb2ops.c
index c36ff0d..aa61dcf 100644
--- a/fs/cifs/smb2ops.c
+++ b/fs/cifs/smb2ops.c
@@ -2917,26 +2917,28 @@ 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);
 }
-- 
2.1.4