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seccomp: document 64-bit argument comparisons and fix masked-equal doc - #133
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kolyshkin
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LGTM overall, thank you @ricardobranco777. Left some nits
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@ricardobranco777 also makes sense to add a link to the same PR for the main libseccomp repo |
The kernel's seccomp filter compares the raw 64-bit argument registers, while syscalls with 32-bit argument types (e.g. the socket(2) domain) ignore the upper 32 bits. A condition such as MakeCondition(0, CompareEqual, unix.AF_NETLINK) is therefore bypassed by socket(0x100000000|AF_NETLINK, ...). Document this in MakeCondition and CompareEqual, and recommend CompareMaskedEqual with a 0xffffffff mask for 32-bit arguments. Also fix the MakeCondition comment on masked equals, which had the operand order reversed: the first value is the mask and the second is the datum. Signed-off-by: Ricardo Branco <rbranco@suse.de>
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Hopefully fixed now. |
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The kernel's seccomp filter compares the raw 64-bit argument registers, while syscalls with 32-bit argument types (e.g. the socket(2) domain) ignore the upper 32 bits. A condition such as
MakeCondition(0, CompareEqual, unix.AF_NETLINK)
is therefore bypassed by socket(0x100000000|AF_NETLINK, ...).
Document this in MakeCondition and CompareEqual, and recommend CompareMaskedEqual with a 0xffffffff mask for 32-bit arguments.
Also fix the MakeCondition comment on masked equals, which had the operand order reversed: the first value is the mask and the second is the datum.
See seccomp/libseccomp#504