Bug #64522 Effective UID issue

Description:
Mysql does not use the effective UID but the real uid.

How to repeat:
login to a server as user_a
sudo su - user_b
  > mysql
  >> ERROR 1045 (28000): Access denied for user 'user_a'@'localhost' (using password: NO)

strace shows the call to geteuid return the correct uid but then mysql checks the content of /proc/self/loginuid which contains the uid of user_a

Here is the end of the strace.
The uid of user_a is 42584 and the uid of user_b is 201
#################
geteuid()                               = 201
open("/proc/self/loginuid", O_RDONLY)   = 4
read(4, "42584", 12)                    = 5
close(4)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(4)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 4
connect(4, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(4)                                = 0
open("/etc/passwd", O_RDONLY|O_CLOEXEC) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=1823, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f98f3b73000
read(4, "root:x:0:0:root:/root:/bin/bash\n"..., 4096) = 1823
close(4)                                = 0
munmap(0x7f98f3b73000, 4096)            = 0
write(3, "(\0\0\1\205\246\3\0\0\0\0\1\10\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 44) = 44
read(3, "I\0\0\2\377\25\4#28000Access denied for u"..., 16384) = 77
shutdown(3, 2 /* send and receive */)   = 0
close(3)                                = 0
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 4), ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f98f3b73000
write(2, "ERROR 1045 (28000): ", 20ERROR 1045 (28000): )    = 20
write(2, "Access denied for user 'user_a'@"..., 64Access denied for user 'user_a'@'localhost' (using password: NO)) = 64
write(2, "\n", 1
)                       = 1
write(1, "\7", 1)                       = 1
exit_group(1)                           = ?

Thank you for the report.

I can not repeat described behavior:

[sveta@delly mysql-test]$ ../client/mysql -S  /home/sveta/src/mysql-trunk/mysql-test/var/tmp/mysqld.1.sock 
ERROR 1045 (28000): Access denied for user 'sveta'@'localhost' (using password: NO)
[sveta@delly mysql-test]$ su
Password: 
[root@delly mysql-test]# ../client/mysql -S  /home/sveta/src/mysql-trunk/mysql-test/var/tmp/mysqld.1.sock 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.6.5-m8-debug-log Source distribution

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> \q
Bye
[root@delly mysql-test]# cat /proc/self/loginuid
500[root@delly mysql-test]# exit
exit
[sveta@delly mysql-test]$ su - root
Password: 
[root@delly ~]# ../client/mysql -S  /home/sveta/src/mysql-trunk/mysql-test/var/tmp/mysqld.1.sock 
-bash: ../client/mysql: No such file or directory
[root@delly ~]# /home/sveta/src/mysql-trunk/mysql-test/../client/mysql -S  /home/sveta/src/mysql-trunk/mysql-test/var/tmp/mysqld.1.sock 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.6.5-m8-debug-log Source distribution

Copyright (c) 2000, 2011, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> \q
Bye

Could you post similar session from your environment?

Hi,

I wasn't able to reproduce this when login as root neither.
Could you please try to login as a user with a uid different than 0?

Thank you for the feedback.

Verified as described:

[sveta@delly mysql-test]$ su - foobar
Password: 
su: warning: cannot change directory to /home/foobar: No such file or directory
-bash-4.1$ home/sveta/src/mysql-5.5/mysql-test/var/tmp/mysqld.1.sock^C
-bash-4.1$ ../client/mysql -h127.0.0.1 -P13000
ERROR 1045 (28000): Access denied for user 'sveta'@'localhost' (using password: NO)

maybe this bit is useful. at least in my environment mysql only does this if .my.cnf file is present (only with [client] and password=aa directives)

so "su - user" with .my.cnf - uses original (wrong) user. without - uses the correct one.

Is this bug fixed?

I'm having similar issues.

I remotely log into a server using opensuse 13.1/mysql  Ver 14.14 Distrib 5.6.12 on 64-bit.

I use sudo to become root
Then I use su to become another user.

If I try to connect to mysql without specifying a user on the command-line client, then it fails with this response:

ERROR 1045 (28000): Access denied for user 'colin'@'localhost' (using password: NO)

This is exactly the behavior described by the original poster.

Fix of bug#64622

Attachment: bug64522.patch (application/octet-stream, text), 756 bytes.