Issue with shell script called from PHP - php

Question

TLDR;
I have a shell script which works fine when run from the command line, but not if called from within a PHP script (accessed via web).
In both cases, the calling user is www-data.
The line failing is this:
openssl genrsa -des3 -out certs/$PCODE.key -passout env:PASSPHRASE 2048
Why is this happening? How can I debug it?
Full story
I have the following script which is a slightly modified version of this gist for generating self-signed SSL certs.
When I run it from the terminal as www-data it works ok and generates the key files, the CSR and the SSL cert file. But when I call the script from within a PHP script, it outputs an error and no files are generated. What is causing the failure? How can I debug this?
From terminal:
me#machine$ sudo su www-data
www-data#machine$ ./gencert.sh acme
www-data will generate an SSL cert for acme.dev
Command after line 32 executed oK
Passphrase expoted as I7gOnWxWd0hOk38Zu ... FbxL3K3Rzlv
Generating RSA private key, 2048 bit long modulus
..............................................+++
.................+++
e is 65537 (0x10001)
Command after line 49 executed oK
Command after line 54 executed oK
Command after line 65 executed oK
writing RSA key
Command after line 69 executed oK
Signature ok
subject=/C=IR/ST=Alborz/.../emailAddress=noreply#acme.dev
Getting Private key
Command after line 74 executed oK
Resulting files:
certs/acme.key.org
certs/acme.key
certs/acme.csr
certs/acme.crt
From PHP:
$r = `/var/www/testbench/pm/shell/gencert.sh acme`;
echo $r;
No files are generated and the output is this:
www-data will generate an SSL cert for acme.dev
Command after line 32 executed oK
Passphrase expoted as 1Fd1seZoe2XF ... oSmQFJdVpdwOeTo2CK5VjLxp
Error. Return value = 1 after line 49
The line returning 1 is this:
openssl genrsa -des3 -out certs/$PCODE.key -passout env:PASSPHRASE 2048
Here is the modified shell script:
#!/bin/bash
# Bash shell script for generating self-signed certs. Run this in a folder, as it
# generates a few files. Large portions of this script were taken from the
# following artcile:
#
# http://usrportage.de/archives/919-Batch-generating-SSL-certificates.html
# https://deliciousbrains.com/ssl-certificate-authority-for-local-https-development/
# Additional alterations by: Brad Landers
# Date: 2012-01-27
# Script accepts a single argument, the fqdn for the cert
PCODE="$1"
if [ -z "$PCODE" ]; then
echo "Usage: $(basename $0) <PCODE>"
exit 11
fi
THE_USER="$(whoami)"
echo "$THE_USER will generate an SSL cert for $PCODE.dev"
fail_if_error() {
[ $1 != 0 ] && {
echo -n "Error. Return value = $1 after line $LASTLINE"
unset PASSPHRASE
exit 10
}
echo "Command after line $LASTLINE executed oK"
}
# Generate a passphrase
LASTLINE="${LINENO}"
export PASSPHRASE=$(head -c 500 /dev/urandom | tr -dc a-z0-9A-Z | head -c 128; echo)
fail_if_error $?
echo -n "Passphrase expoted as "
printenv PASSPHRASE
# Certificate details; replace items in angle brackets with your own info
subj="
C=IR
ST=Alborz
O=ACME
localityName=Karaj
commonName=*.$PCODE.dev
organizationalUnitName=WebAdmin
emailAddress=noreply#$PCODE.dev
"
LASTLINE="${LINENO}"
# Generate the server private key
openssl genrsa -des3 -out certs/$PCODE.key -passout env:PASSPHRASE 2048
fail_if_error $?
LASTLINE="${LINENO}"
# Generate the CSR
openssl req \
-new \
-batch \
-subj "$(echo -n "$subj" | tr "\n" "/")" \
-key certs/$PCODE.key \
-out certs/$PCODE.csr \
-passin env:PASSPHRASE
fail_if_error $?
LASTLINE="${LINENO}"
cp certs/$PCODE.key certs/$PCODE.key.org
fail_if_error $?
LASTLINE="${LINENO}"
# Strip the password so we don't have to type it every time we restart Apache
openssl rsa -in certs/$PCODE.key.org -out certs/$PCODE.key -passin env:PASSPHRASE
fail_if_error $?
LASTLINE="${LINENO}"
# Generate the cert (good for 10 years)
openssl x509 -req -days 3650 -in certs/$PCODE.csr -signkey certs/$PCODE.key -out certs/$PCODE.crt
fail_if_error $?

Answer 1

The command you want to execute has relative paths, eg: certs/$PCODE.key. When you exec the commands (via the backtick operator in this case), the paths are expanded relative to the PHP process' current working directory. This is rarely, if ever, the same path as your command shell uses.
To debug this, you can extend your actual command with strace, eg: strace openssl .... This will give you considerable diagnostics and, near the end, you'll see something along the lines of EPERM.
To fix this, you can either use chdir in your PHP to set the current working directory, or you can cd in your script, or your script can use absolute paths. I'd prefer the latter.