PlatformInit resets signal handlers to SIG_DFL causing crashes #47013
Comments
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I'm a bit torn on whether to add workarounds for dodgy LD_PRELOAD wrappers but philosophical objections aside, I don't think node can detect their presence in a race-free manner. If third-party code can run really early, then it can call sigaction() from a newly started thread. Meaning this won't work: sigaction(nr, nullptr, &old);
// <-- sigaction()-from-other-thread race window here
if (old.sa_handler == SIG_DFL) sigaction(nr, &act, nullptr);And neither will this: sigaction(nr, &act, &old);
// <-- signal delivery race window here
if (old.sa_handler != SIG_DFL) sigaction(nr, &old, nullptr);(And I'm skipping over the practical concern that reading |
Yes, this won't work and looks wild. I don't think we should be bothered with such possibilities. Signal handlers are inherently global and shouldn't be changed asynchronously. A normal sequential check for existing handlers sounds reasonable.
The code currently does: so presumably at least this is working fine on all platforms. |
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Yes, because The real logic should look something like this, and, caveat emptor, I'm not 100% sure this won't emit warnings or isn't UB according to POSIX: if ((old.sa_flags & SA_SIGINFO) && old.sa_sigaction == SIG_DFL || old.sa_handler == SIG_DFL)Well, pull request welcome, I suppose. |
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@dvyukov are you interested in pursuing this? If not, all good, but then I'll go ahead and close this out. |
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Yes, I am. I just somehow missed your previous reply. |
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There's test/embedding/embedtest.cc and concomitant JS file but I wouldn't want to vouch it's the right place because it also doubles as an embedding example. I'd be okay with just an Obviously Correct Looking(TM) code change. |
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix nodejs#47013
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix nodejs#47013
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
The only bad handler value we can inhert from before exec is SIG_IGN (any actual function pointer is reset to SIG_DFL during exec). If that's the case, we want to reset it back to SIG_DFL. However, it's also possible that an embeder (or an LD_PRELOAD-ed library) has set up own signal handler for own purposes (e.g. profiling). If that's the case, keep it intact. Fix #47013 PR-URL: #47188 Reviewed-By: Ben Noordhuis <[email protected]> Reviewed-By: James M Snell <[email protected]>
Version
0c46051
Platform
Linux 5.19.11-amd64 #1 SMP x86_64 GNU/Linux
Subsystem
No response
What steps will reproduce the bug?
LD_PRELOAD or link in any library that sets a signal handler and schedules signal delivery (e.g. a posix timer).
How often does it reproduce? Is there a required condition?
No response
What is the expected behavior?
The library handles own signals.
What do you see instead?
The program crashes.
Additional information
#615 added this code that resets all signal handlers to SIG_DFL:
node/src/node.cc
Lines 426 to 434 in 0c46051
This causes crashes is there is a signal handler installed.
While SIG_IGN can indeed be inherited across execve, all actual handlers (not SIG_IGN/DFL) are reset to SIG_DFL.
So I think the startup code should reset to SIG_DFL iff the handler is set of SIG_IGN. Any real handlers should be left intact.
@bnoordhuis @sam-github @melver
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