How to compare string values with seccomp?

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Some Linux system calls (such as execve, openat) have string type arguments. But the comparison function SCMP_CMP provided by seccomp seems to be comparing two pointers. So how can I limit files that can be opened by a process to a specific dir using seccomp? Is there a way for users to provide a general comparison function?










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  • Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

    – Cyker
    Jan 2 at 19:58











  • Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

    – ilkkachu
    Jan 2 at 20:28











  • In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

    – ilkkachu
    Jan 2 at 20:31











  • According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

    – Mark Plotnick
    Jan 3 at 21:55











  • One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

    – Mark Plotnick
    Jan 3 at 22:06















5















Some Linux system calls (such as execve, openat) have string type arguments. But the comparison function SCMP_CMP provided by seccomp seems to be comparing two pointers. So how can I limit files that can be opened by a process to a specific dir using seccomp? Is there a way for users to provide a general comparison function?










share|improve this question






















  • Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

    – Cyker
    Jan 2 at 19:58











  • Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

    – ilkkachu
    Jan 2 at 20:28











  • In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

    – ilkkachu
    Jan 2 at 20:31











  • According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

    – Mark Plotnick
    Jan 3 at 21:55











  • One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

    – Mark Plotnick
    Jan 3 at 22:06













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Some Linux system calls (such as execve, openat) have string type arguments. But the comparison function SCMP_CMP provided by seccomp seems to be comparing two pointers. So how can I limit files that can be opened by a process to a specific dir using seccomp? Is there a way for users to provide a general comparison function?










share|improve this question














Some Linux system calls (such as execve, openat) have string type arguments. But the comparison function SCMP_CMP provided by seccomp seems to be comparing two pointers. So how can I limit files that can be opened by a process to a specific dir using seccomp? Is there a way for users to provide a general comparison function?







linux syscalls






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share|improve this question











share|improve this question




share|improve this question










asked Jan 2 at 18:59









CykerCyker

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1,45021531












  • Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

    – Cyker
    Jan 2 at 19:58











  • Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

    – ilkkachu
    Jan 2 at 20:28











  • In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

    – ilkkachu
    Jan 2 at 20:31











  • According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

    – Mark Plotnick
    Jan 3 at 21:55











  • One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

    – Mark Plotnick
    Jan 3 at 22:06

















  • Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

    – Cyker
    Jan 2 at 19:58











  • Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

    – ilkkachu
    Jan 2 at 20:28











  • In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

    – ilkkachu
    Jan 2 at 20:31











  • According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

    – Mark Plotnick
    Jan 3 at 21:55











  • One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

    – Mark Plotnick
    Jan 3 at 22:06
















Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

– Cyker
Jan 2 at 19:58





Hmm, why do some people suggest this question doesn't fit here, given the fact that seccomp is built in the Linux kernel...

– Cyker
Jan 2 at 19:58













Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

– ilkkachu
Jan 2 at 20:28





Ho hum, I would have thought this to be on-topic, based on the "C API and system interfaces" point in the help page, and the fact that it's specific to an OS that matches the description "Unix & Linux". But apparently the consensus on the discussion in meta is that interfaces like that aren't on-topic since "only programmers see them".

– ilkkachu
Jan 2 at 20:28













In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

– ilkkachu
Jan 2 at 20:31





In any case, there's even a tag for seccomp on stackoverflow, so chances are there's someone there who knows something about it.

– ilkkachu
Jan 2 at 20:31













According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

– Mark Plotnick
Jan 3 at 21:55





According to this talk (at the 8 minute mark) from a few months ago, pointer dereferencing in seccomp bpf is not yet possible, but is being worked on.

– Mark Plotnick
Jan 3 at 21:55













One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

– Mark Plotnick
Jan 3 at 22:06





One issue with trying to read process memory as a security check is that there's a TOCTOU race if you have multiple threads or shared/ mmapped memory.

– Mark Plotnick
Jan 3 at 22:06










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