Details
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Task
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Status: Open (View Workflow)
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Minor
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Resolution: Unresolved
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None
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None
Description
In MariaDB 10.4, version 2 of the pam plugin is provided. This plugin forks a new process and executes the auth_pam_tool utility that is now bundled with the server.
There are probably going to be cases where people need to execute this tool manually as a test. Unfortunately, the input format of this tool is not very user friendly.
One method that can be used to construct the tool's input and run the tool for testing purposes is described below.
Configuring PAM
First we can configure PAM.
Create a Unix user account and set a password for the user:
sudo useradd alice
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sudo passwd alice
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Create the PAM service configuration:
sudo tee /etc/pam.d/mariadb <<EOF
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auth required pam_unix.so audit
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account required pam_unix.so audit
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EOF
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And then you might need to execute some commands to work around MDEV-19876:
sudo chmod 0755 /usr/lib64/mysql/plugin/auth_pam_tool_dir/
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sudo chmod 4755 /usr/lib64/mysql/plugin/auth_pam_tool_dir/auth_pam_tool
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Configuring MariaDB
We can configure MariaDB to use PAM authentication for this user account.
Let's install the pam plugin:
INSTALL SONAME 'auth_pam';
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And let's create the relevant user:
CREATE USER 'alice'@'localhost' IDENTIFIED VIA pam USING 'mariadb'
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Constructing the Input
Next we can construct the input for the auth_pam_tool tool.
As far as I can tell, the input format of the data that needs to be passed to stdin is:
<control flag field><length of user name field as 2-byte integer><user name field><length of auth string field as 2-byte integer><auth string field><length of password field as 2-byte integer><password field>
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So let's say that we have the following values:
control flag:
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string=0
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user name:
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string=alice
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length=5
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length as 2 bytes in hex = 0x05
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auth string:
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string=mariadb
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length=7
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length as 2 bytes in hex = 0x07
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password:
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string=uGBXHxID3dJRALw2
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length=16
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length as 2 bytes in hex = 0x10
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So that would make the stdin data:
0\x05alice\x07mariadb\x10uGBXHxID3dJRALw2
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Let's create input with a null-terminated password:
echo -n -e '0\0\x05alice\0\x07mariadb\0\x11uGBXHxID3dJRALw2\0' > good_input.txt
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And let's also create input with a password that is not null-terminated:
echo -n -e '0\0\x05alice\0\x07mariadb\0\x10uGBXHxID3dJRALw2' > bad_input.txt
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And then confirm the contents of each file:
$ hexdump -c good_input.txt
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0000000 0 \0 005 a l i c e \0 \a m a r i a d
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0000010 b \0 021 u G B X H x I D 3 d J R A
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0000020 L w 2 \0
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0000024
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$ hexdump -c bad_input.txt
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0000000 0 \0 005 a l i c e \0 \a m a r i a d
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0000010 b \0 020 u G B X H x I D 3 d J R A
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0000020 L w 2
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0000023
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Running the Tool
Next, we can run the auth_pam_tool tool and redirect the tool's stdin to the input files that we constructed.
We can also attach strace to the process, so we can passwords the tool is reading and writing.
First, run the tool with the good input:
cat good_input.txt | sudo strace -o strace_good_input.out -f -ff /usr/lib64/mysql/plugin/auth_pam_tool_dir/auth_pam_tool
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The null-terminated password is properly read and passed to PAM:
write(1, "C", 1) = 1
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write(1, "\0\v", 2) = 2
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write(1, "\4Password: ", 11) = 11
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read(0, "\0\21", 2) = 2
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read(0, "uGBXHxID3dJRALw2\0", 17) = 17
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...
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write(4, "uGBXHxID3dJRALw2", 16) = 16
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write(4, "\0", 1) = 1
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Next, run the tool with the bad input:
cat bad_input.txt | sudo strace -o strace_bad_input.out -f -ff /usr/lib64/mysql/plugin/auth_pam_tool_dir/auth_pam_tool
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The non-null-terminated password is properly read, but its last character is truncated when it is passed to PAM due to MDEV-19882:
write(1, "C", 1) = 1
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write(1, "\0\v", 2) = 2
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write(1, "\4Password: ", 11) = 11
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read(0, "\0\20", 2) = 2
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read(0, "uGBXHxID3dJRALw2", 16) = 16
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...
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write(4, "uGBXHxID3dJRALw", 15) = 15
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write(4, "\0", 1) = 1
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Checking Syslog
The syslog (i.e. /var/log/secure on RHEL or /var/log/auth.log on Debian/Ubuntu) also shows an authentication failure, since the auth_pam_tool
tool provided a truncated password to PAM:
Oct 16 02:24:14 ip-172-30-0-123 unix_chkpwd[11398]: password check failed for user (alice)
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Oct 16 02:24:14 ip-172-30-0-123 auth_pam_tool: pam_unix(mariadb:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost= user=alice
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Attachments
Issue Links
- is caused by
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- Closed
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- Closed
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- relates to
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MDEV-19878 pam v2: pam password authentication doesn't work at all
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- Closed
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- Closed
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- Closed
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- Open
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- Closed
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- Closed
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- Stalled
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