Issues with vsftpd Service

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Environment

SUSE Linux Enterprise Server 12

SUSE Linux Enterprise Server 15

Situation

- Local users can no longer authenticate to FTP service after the system has been joined to AD
- Listing directory "ls" that contains more than one million "too many files" files failing with errors

An example of the error messages are:

vsftpd[30863]: pam_winbind(vsftpd:auth): request wbcLogonUser failed: WBC_ERR_AUTH_ERROR, PAM error: PAM_USER_UNKNOWN (10), NTSTATUS: NT_STATUS_NO_SUCH_USER, Error message was: No such user

or

vsftpd[30863]: pam_winbind(vsftpd:auth): internal module error (retval = PAM_AUTHINFO_UNAVAIL(9), user = '...')

This above issue sometimes occurs after system migration, for example from SLES 11 to SLES 12.

Resolution

To solve above issue, you need to increase the address space limit of vsftpd, this can be done by adjusting or adding the address_space_limit parameter in /etc/vsftpd.conf ; E.g. address_space_limit=157286401 (150MB) The maximum value for this parameter is : 4294967295 (4GB)

Cause

The vsftpd process is getting out-of-memory resulting in failed pam module.

Additional Information

The address_space_limit adjusts the amount of memory vsftpd can use (in bytes). This limit exists so that attackers cannot exploit any potential bugs in the server that might result in vsftpd allocating huge amounts of memory that would affect the host system negatively, e.g. causing thrashing or killing random processes due to Linux's OOM system. If the value is configured too low, vsftpd will fail with "out of memory" errors during normal operations. Oftentimes, this occurs inside of the PAM stack on systems that have many memory-intensive PAM modules enabled, as the default hardcoded value of 104857600 (100MB) might not be enough. By migrating from older to newer SLES releases, the memory requirement of those memory-intensive PAM modules might increase, requiring manual adjustment of vsftpd's memory limit.

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