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For example, the variable allow is placed at offset -4 from the frame pointer and this value is used by IDA in the disassembly listing for the symbolic name instead of raw numerical offset. In some cases, like in the example above, it is an actual processor register ( RBP). Frame offsets and stack variablesĪs mentioned above, in the stack frame view structure offsets are shown relative to the frame pointer.
Ida pro pseudocode code#
Since the code is only checking for a non-zero value, this will bypass the check and result in the execution of the privilegedAction function. We can also rename the variables to their proper names.īecause IDA shows the stack frame layout in the natural memory order (addresses increase towards the bottom), we can immediately see the problem demonstrated by the vulnerable code: the gets function has no bounds checking, so entering a long string can overflow the username buffer and overwrite the allow variable. To improve it, press * on var_10 and convert it into an array of 8 bytes.
Ida pro pseudocode full size#
Because the code only takes the address of start of the buffer, IDA could not detect its full size and created a single byte variable. On opening the stack frame we can see the following picture:īy comparing the source code and disassembly, we can infer that var_10 is username and var_4 is allow. Gets(username) // user inputs "malicious" Printf external link("Enter your username, please: ") Create arrays ( *) or structure instances ( Alt– Q)Ĭonsider this vulnerable program: #include.Define new or change existing stack variables ( D).In this view, you can perform most of the same operations as in the Structures view: Double-click or press Enter on a stack variable in the disassembly or pseudocode.Edit > Functions > Stack variables… or press Ctrl– K while positioned in a function in disassembly (IDA View).It may contain special members to represent the saved return address and/or saved register area.Instead of offsets from the structure start, offsets from the frame pointer are shown (both positive and negative).The frame structure has no name and is not included in the global Structures list it can only be reached from the corresponding function.This structure is very similar to other structures in the Structures view, with a few differences: Thus, IDA uses a pseudo structure to represent its layout. the return address on x86).īecause the stack may change unpredictably during execution, the stack frame and its parts do not have a fixed address. incoming arguments (for calling conventions which use stack for passing arguments).The stack frame usually contains data such as: The s tack frame is part of the stack which is managed by the current function and contains the data used by it.