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In the Linux kernel, the following vulnerability has been resolved: x86/fpu: Stop relying on userspace for info to fault in xsave buffer Before this change, the expected size of the user space buffer was taken from fx_sw->xstate_size. fx_sw->xstate_size can be changed from user-space, so it is possible construct a sigreturn frame where: * fx_sw->xstate_size is smaller than the size required by valid bits in fx_sw->xfeatures. * user-space unmaps parts of the sigrame fpu buffer so that not all of the buffer required by xrstor is accessible. In this case, xrstor tries to restore and accesses the unmapped area which results in a fault. But fault_in_readable succeeds because buf + fx_sw->xstate_size is within the still mapped area, so it goes back and tries xrstor again. It will spin in this loop forever. Instead, fault in the maximum size which can be touched by XRSTOR (taken from fpstate->user_size). [ dhansen: tweak subject / changelog ]
CVSS 3.1 Base Score 5.5. CVSS Attack Vector: local. CVSS Attack Complexity: low. CVSS Vector: (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).
In the following code the method processMessagesFromServer attempts to establish a connection to a server and read and process messages from the server. The method uses a do/while loop to continue trying to establish the connection to the server when an attempt fails.
}
...// create socket to connect to server
}// establish connection to server// if connected then read and process messages from server
...// read and process messages// keep trying to establish connection to the server// close socket and return success or failureHowever, this will create an infinite loop if the server does not respond. This infinite loop will consume system resources and can be used to create a denial of service attack. To resolve this a counter should be used to limit the number of attempts to establish a connection to the server, as in the following code.
}
...// initialize number of attempts counter
}// establish connection to server// increment counter// if connected then read and process messages from server
...// read and process messages// keep trying to establish connection to the server// up to a maximum number of attempts// close socket and return success or failureFor this example the method isReorderNeeded as part of a bookstore application that determines if a particular book needs to be reordered based on the current inventory count and the rate at which the book is being sold.
}
return isReorder;// get inventory count for book// find number of days until inventory count reaches minimum
days++;// if number of days within reorder timeframe// set reorder return boolean to trueisReorder = true;However, the while loop will become an infinite loop if the rateSold input parameter has a value of zero since the inventoryCount will never fall below the minimumCount. In this case the input parameter should be validated to ensure that a value of zero does not cause an infinite loop,as in the following code.
}
...// validate rateSold variablereturn isReorder;ExploitPedia is constantly evolving. Sign up to receive a notification when we release additional functionality.
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