celtera
SIGSEGV when access to /dev/snd/seq is denied
Linux here, Arch. My user wasn't part of the 'audio' group, and ALSA denies access to /dev/snd/seq. So this was solved after adding the user to 'audio'. (strangely, it did actually work for a couple days like this -maybe it was through a different API?)
Anyway, it crashed under that situation: SIGSEGV when 'ALSA lib seq_hw.c:540:(snd_seq_hw_open) open /dev/snd/seq failed: Permission denied' happens, in:
snd_seq_poll_descriptors:
endbr64
test $0x1,%cl
je 0x7ffff7b009c0 <snd_seq_poll_descriptors+48>
xor %eax,%eax
test %edx,%edx
je 0x7ffff7b009cb <snd_seq_poll_descriptors+59>
and $0x4,%ecx
mov 0x14(%rdi),%edx
cmp $0x1,%cx
sbb %eax,%eax
mov %edx,(%rsi) <===
and $0xfffffffc,%eax
add $0x2d,%eax
mov %ax,0x4(%rsi)
mov $0x1,%eax
ret
nopl (%rax)
and $0x4,%ecx
je 0x7ffff7b009c9 <snd_seq_poll_descriptors+57>
test %edx,%edx
jne 0x7ffff7b009d0 <snd_seq_poll_descriptors+64>
xor %eax,%eax
ret
nopl 0x0(%rax)
mov 0x14(%rdi),%edx
mov $0x2c,%eax
mov %ax,0x4(%rsi)
mov $0x1,%eax
mov %edx,(%rsi)
ret
Apologies if the disassembly doesn't help. Anyway, I think the case of forbidden access to /dev/snd/seq could be handled more gracefully.
hello, thanks for the report! are you on the last version? as there is the following check exactly for this: https://github.com/celtera/libremidi/blob/master/include/libremidi/backends/alsa_seq.hpp#L45
If /dev/snd/seq cannot be opened, the alsa seq backend won't even be listed as an available backend.
Ah nevermind, the code checks for existence but not for read / write access ; I'll fix this