From 9ee803bfdba0cf739038dbdabdd4c02582c8f2b2 Mon Sep 17 00:00:00 2001 From: Paulo Alcantara Date: Fri, 13 Mar 2026 00:03:38 -0300 Subject: [PATCH] smb: client: fix krb5 mount with username option commit 12b4c5d98cd7ca46d5035a57bcd995df614c14e1 upstream. Customer reported that some of their krb5 mounts were failing against a single server as the client was trying to mount the shares with wrong credentials. It turned out the client was reusing SMB session from first mount to try mounting the other shares, even though a different username= option had been specified to the other mounts. By using username mount option along with sec=krb5 to search for principals from keytab is supported by cifs.upcall(8) since cifs-utils-4.8. So fix this by matching username mount option in match_session() even with Kerberos. For example, the second mount below should fail with -ENOKEY as there is no 'foobar' principal in keytab (/etc/krb5.keytab). The client ends up reusing SMB session from first mount to perform the second one, which is wrong. ``` $ ktutil ktutil: add_entry -password -p testuser -k 1 -e aes256-cts Password for testuser@ZELDA.TEST: ktutil: write_kt /etc/krb5.keytab ktutil: quit $ klist -ke Keytab name: FILE:/etc/krb5.keytab KVNO Principal ---- ---------------------------------------------------------------- 1 testuser@ZELDA.TEST (aes256-cts-hmac-sha1-96) $ mount.cifs //w22-root2/scratch /mnt/1 -o sec=krb5,username=testuser $ mount.cifs //w22-root2/scratch /mnt/2 -o sec=krb5,username=foobar $ mount -t cifs | grep -Po 'username=\K\w+' testuser testuser ``` Reported-by: Oscar Santos Signed-off-by: Paulo Alcantara (Red Hat) Cc: David Howells Cc: linux-cifs@vger.kernel.org Cc: stable@vger.kernel.org Signed-off-by: Steve French Signed-off-by: Greg Kroah-Hartman --- fs/smb/client/connect.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/smb/client/connect.c b/fs/smb/client/connect.c index dd7f48f53097..7bc912d00030 100644 --- a/fs/smb/client/connect.c +++ b/fs/smb/client/connect.c @@ -1954,6 +1954,10 @@ static int match_session(struct cifs_ses *ses, case Kerberos: if (!uid_eq(ctx->cred_uid, ses->cred_uid)) return 0; + if (strncmp(ses->user_name ?: "", + ctx->username ?: "", + CIFS_MAX_USERNAME_LEN)) + return 0; break; case NTLMv2: case RawNTLMSSP: