https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=204097
Bug ID: 204097
Summary: witness_initialize() does not perform bound checking
of witness_count
Product: Base System
Version: 11.0-CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: kern
Assignee: freebsd-bugs@FreeBSD.org
Reporter: ertl.ch...@gmail.com
The witness_count sysctl node is of type CTLFLAG_RDTUN, which means it's a
read-only variable, but can be set during boot by creating a
"debug.witness.count" entry in /boot/loader.conf.
The witness_initialize() function of sys/kern/subr_witness.c does not perform
bound checks on witness_count which could lead to integer overflows, and memory
corruption.
The following line from witness_initialize() can cause an overflow, if
witness_count is 2147483647 for example, since a signed comparison is used:
for (i = 0; i < witness_count + 1; i++) {
This means that the w_rmatrix[i] buffers are never allocated, which would lead
to kernel reads and writes from an uninitialized pointer.
A potential fix would be to add the following bound check at the beginning of
the function:
if (witness_count < 0 || witness_count >= 2147483647) {
printf("Invalid witness_count value of %d, setting to 2147483646\n",
witness_count);
witness_count = 2147483646;
}
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