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Kernel: Validate the full range of user memory passed to syscalls

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We now validate the full range of userspace memory passed into syscalls
instead of just checking that the first and last byte of the memory are
in process-owned regions.

This fixes an issue where it was possible to avoid rejection of invalid
addresses that sat between two valid ones, simply by passing a valid
address and a size large enough to put the end of the range at another
valid address.

I added a little test utility that tries to provoke EFAULT in various
ways to help verify this. I'm sure we can think of more ways to test
this but it's at least a start. :^)

Thanks to mozjag for pointing out that this code was still lacking!

Incidentally this also makes backtraces work again.

Fixes #989.
This commit is contained in:
Andreas Kling 2020-01-02 02:09:25 +01:00
parent e5ffa960d7
commit 3dcec260ed
4 changed files with 121 additions and 25 deletions
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18
Kernel/Process.cpp
View file

@ -1958,7 +1958,7 @@ bool Process::validate_read_from_kernel(VirtualAddress vaddr, ssize_t size) cons
return false;
if (is_kmalloc_address(vaddr.as_ptr()))
return true;
return validate_read(vaddr.as_ptr(), size);
return MM.validate_kernel_read(*this, vaddr, size);
}
bool Process::validate_read_str(const char* str)
@ -1984,23 +1984,15 @@ bool Process::validate_read(const void* address, ssize_t size) const
if (is_kmalloc_address(address))
return true;
}
ASSERT(size);
if (!size)
return false;
if (first_address.page_base() != last_address.page_base()) {
if (!MM.validate_user_read(*this, last_address))
return false;
}
return MM.validate_user_read(*this, first_address);
return MM.validate_user_read(*this, first_address, size);
}
bool Process::validate_write(void* address, ssize_t size) const
{
ASSERT(size >= 0);
VirtualAddress first_address((u32)address);
VirtualAddress last_address = first_address.offset(size - 1);
if (last_address < first_address)
return false;
if (is_ring0()) {
if (is_kmalloc_address(address))
return true;
@ -2012,11 +2004,7 @@ bool Process::validate_write(void* address, ssize_t size) const
}
if (!size)
return false;
if (first_address.page_base() != last_address.page_base()) {
if (!MM.validate_user_write(*this, last_address))
return false;
}
return MM.validate_user_write(*this, first_address);
return MM.validate_user_write(*this, first_address, size);
}
pid_t Process::sys$getsid(pid_t pid)