lslogins: fix lastlog2 tty/host buffer overflow in get_lastlog2#4418
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get_lastlog2() copies the TTY and host strings read from the lastlog2 database into heap buffers of sizeof(ut_line)+1 and sizeof(ut_host)+1 bytes, but passed strlen(value)+1 as the mem2strcpy() limit. mem2strcpy() zero-fills and copies that many bytes regardless of the destination, so a database value longer than the field overflows the buffer. Cap the limit to the destination field size, matching the wtmp and plain-lastlog paths in the same function. Signed-off-by: aizu-m <aizumusheer2@gmail.com>
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Comparing the lastlog2 reader against the wtmp branch in the same function, the last mem2strcpy() argument looked wrong, so I traced it.
Under ASAN a host longer than 256 bytes gives a heap-buffer-overflow one byte after the 257-byte buffer (the memset). The values reach the database from pam_lastlog2 (PAM_TTY/PAM_RHOST, stored untruncated) or from any database handed to lslogins with --lastlog2-file. Capped the limit to the destination field size, which is what the wtmp and plain-lastlog branches just above already do.