[Backport v4.3-branch] net: dns: Fix potential buffer overflow when unpacking labels #99830
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As the loop unpacking the DNS name from records checks the current label length on each iteration, it's also needed to update the remaining buffer length on each iteration, otherwise the buffer length checks doesn't work as expected. Additionally, the remaining buffer checks while technically worked, they were conceptually wrong and unintuitive. The buf->data pointer doesn't move, so comparing against this pointer when adding new labels doesn't make sense. It's more intuitive to simply compare the label size vs the remaining buffer space. Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no> (cherry picked from commit 7bd45cd)
Verify that dns_unpack_name() generates a valid DNS name when unpacking records and that it returns an error in case of overflow. Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no> (cherry picked from commit 7a9ca8e)
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jukkar
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Nov 22, 2025
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Backport 7a9ca8e~2..7a9ca8e from #99683.
Fixes #99682