Problems using libsrtp on EL9

miken32 0
Viewed 19

I'm having some issues with enabling the res_srtp module in Asterisk. Every attempt results in this not-so-helpful error message:

WARNING[47044] res_srtp.c: Failed to initialize libsrtp
ERROR[47044] loader.c: *** Failed to load module res_srtp.so
ERROR[47044] asterisk.c: Module initialization failed. ASTERISK EXITING!

I'd like to fix this and get it running, so now we get into the programming side of things. I'm not a C programmer by trade, but I was able to use my limited gdb skills to trace the error back through libsrtp's crypto_kernel_init() function. The error occurs when trying to enable the AES-GCM-128 cipher.

I was only able to get as far as PK11_Encrypt() in the NSS library, where I was unable to step into this line of code. I think this is because (again, very limited C knowledge) it's a macro and not a true function?

crv = PK11_GETTAB(slot)->C_EncryptInit(session, &mech, symKey->objectID);
// returns 113

So my question is either, how can I proceed with debugging this to a point where I can file a bug report with someone, or (preferably) has anyone got libsrtp working in this environment? There were very few other reports of similar problems, likely because EL9 is not in wide use yet.

My distro (AlmaLinux) is running NSS 3.71, and I've tried updating to NSS 3.79 with no change.

Here's the backtrace from where I was able to get to, if it's of any help.

#0  PK11_Encrypt (symKey=0x555555ea1a00, mechanism=mechanism@entry=4231, param=param@entry=0x7fffffffc9a0, 
    out=out@entry=0x7fffffffcb50 "\331\061\062%\370\204\006\345\245Y\tů\365&\232\206\247\251S\025\064\367\332.L0=\212\061\212r\034<\f\225\225h\tS/\317\016$I\246\265%\261j\355\365\252\r\346W\272c{9", outLen=outLen@entry=0x7fffffffca3c, maxLen=<optimized out>, 
    data=0x7fffffffcb50 "\331\061\062%\370\204\006\345\245Y\tů\365&\232\206\247\251S\025\064\367\332.L0=\212\061\212r\034<\f\225\225h\tS/\317\016$I\246\265%\261j\355\365\252\r\346W\272c{9", dataLen=60) at ../pk11wrap/pk11obj.c:972
#1  0x00007ffff456a455 in srtp_aes_gcm_nss_do_crypto (enc_len=0x7fffffffca3c, 
    buf=0x7fffffffcb50 "\331\061\062%\370\204\006\345\245Y\tů\365&\232\206\247\251S\025\064\367\332.L0=\212\061\212r\034<\f\225\225h\tS/\317\016$I\246\265%\261j\355\365\252\r\346W\272c{9", encrypt=1, cv=0x5555562a19c0) at crypto/cipher/aes_gcm_nss.c:297
#2  srtp_aes_gcm_nss_encrypt (cv=0x5555562a19c0, buf=<optimized out>, enc_len=0x7fffffffca3c) at crypto/cipher/aes_gcm_nss.c:345
#3  0x00007ffff456cb24 in srtp_cipher_type_test (ct=0x7ffff457a6c0 <srtp_aes_gcm_128>, test_data=0x7ffff457a420 <srtp_aes_gcm_test_case_0>)
    at crypto/cipher/cipher.c:297
#4  0x00007ffff456d545 in srtp_cipher_type_test (ct=<optimized out>, test_data=<optimized out>) at crypto/cipher/cipher.c:605
#5  0x00007ffff456d58d in srtp_cipher_type_self_test (ct=<optimized out>) at crypto/cipher/cipher.c:613
#6  0x00007ffff457005d in srtp_crypto_kernel_do_load_cipher_type (replace=0, id=6, new_ct=0x7ffff457a6c0 <srtp_aes_gcm_128>)
    at crypto/kernel/crypto_kernel.c:293
#7  srtp_crypto_kernel_load_cipher_type (new_ct=new_ct@entry=0x7ffff457a6c0 <srtp_aes_gcm_128>, id=id@entry=6) at crypto/kernel/crypto_kernel.c:343
#8  0x00007ffff457036e in srtp_crypto_kernel_init () at crypto/kernel/crypto_kernel.c:139
#9  srtp_crypto_kernel_init () at crypto/kernel/crypto_kernel.c:72
#10 0x00007ffff457040d in srtp_init () at srtp/srtp.c:2729
#11 0x00007ffff458718d in res_srtp_init () at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/res/res_srtp.c:1237
#12 load_module () at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/res/res_srtp.c:1272
#13 0x000055555566c4dc in start_resource.part.0.lto_priv.0 (mod=0x555555a469d0) at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:1718
#14 0x0000555555665517 in start_resource (mod=0x555555a469d0) at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:1692
#15 start_resource_attempt (mod=mod@entry=0x555555a469d0, count=count@entry=0x7fffffffce94)
    at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:1894
#16 0x000055555566862f in start_resource_list (mod_count=0x7fffffffce94, resources=0x7fffffffceb0)
    at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:1991
#17 load_resource_list (mod_count=<synthetic pointer>, load_order=0x7fffffffcea0) at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:2173
#18 load_modules () at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/loader.c:2396
#19 0x000055555559e074 in asterisk_daemon (isroot=<optimized out>, rungroup=<optimized out>, runuser=<optimized out>)
    at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/asterisk.c:4258
#20 main (argc=<optimized out>, argv=<optimized out>) at /usr/src/debug/asterisk-16.28.0-0.el9.x86_64/main/asterisk.c:4025
rhel9 nss gdb c
1 Answers

After going through the debug steps a few more times, I tried searching the initial return value from srtp_kernel_init() which was srtp_err_status_cipher_fail; I ended up finding a resolved issue with the same symptoms for Fedora Linux:

The issue turns out to be an incompatibility with nss-3.63 shipped with F34. The attached patch adds NSS_PKCS11_2_0_COMPAT defines to 2 header files to enable the backward compatibility. The same fix is already in the upstream github repo and is targeted for the next libsrtp release.

I was able to apply their patch to the libsrtp 2.3.0 codebase, and the library is successfully loading now:

index 4d6031f..b1da343 100644
--- a/crypto/include/aes_gcm.h
+++ b/crypto/include/aes_gcm.h
@@ -66,6 +66,8 @@ typedef struct {
 
 #ifdef NSS
 
+#define NSS_PKCS11_2_0_COMPAT 1
+
 #include <nss.h>
 #include <pk11pub.h>
 
index ad306dd..a57564f 100644
--- a/crypto/include/aes_icm_ext.h
+++ b/crypto/include/aes_icm_ext.h
@@ -65,6 +65,8 @@ typedef struct {
 
 #ifdef NSS
 
+#define NSS_PKCS11_2_0_COMPAT 1
+
 #include <nss.h>
 #include <pk11pub.h>

I'm not sure the second hunk is needed, as ICM ciphers were loading fine, but I applied it anyway.

miken320
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