CVE-2026-31392

01/Description

In the Linux kernel, the following vulnerability has been resolved: smb: client: fix krb5 mount with username option 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 [email protected]: ktutil: write_kt /etc/krb5.keytab ktutil: quit $ klist -ke Keytab name: FILE:/etc/krb5.keytab KVNO Principal ---- ---------------------------------------------------------------- 1 [email protected] (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 ```

02/Affected products

linux: linux kernel

03/References6

• git.kernel.org/stable/c/12b4c5d98cd7ca46d5035a57bcd995df614c14e1 Patch
• git.kernel.org/stable/c/6e9ff1eb7feedcf46ff2d0503759960ab58e7775 Patch
• git.kernel.org/stable/c/9229709ec8bf85ae7ca53aeee9aa14814cdc1bd2 Patch
• git.kernel.org/stable/c/9ee803bfdba0cf739038dbdabdd4c02582c8f2b2 Patch
• git.kernel.org/stable/c/d33cbf0bf8979d779900da9be2505d68d9d8da25 Patch
• git.kernel.org/stable/c/fd4547830720647d4af02ee50f883c4b1cca06e4 Patch