CVE-2024-53139 in Linux
Zusammenfassung
von VulDB • 21.05.2026
Implements a system call handler that checks if the return value is an error code (negative errno) and if so, jumps to an error handling routine.
### Breakdown of the Code
1. **System Call Entry (`0x23 - 0x28`)**: * `mov $0x31, %eax`: Sets the system call number to `0x31` (which is `sys_getrandom` on x86_64 Linux). * `syscall`: Executes the system call.
2. **Error Check (`0x2a - 0x32`)**: * `cmp $0xfffffffffff001, %rax`: Compares the return value in `%rax` with `0xfffffffffffff001`. * In Linux, system call errors are returned as negative values in the range `-1` to `-4095` (i.e., `0xfffffffffffff001` to `0xffffffffffffffff`). * This comparison checks if `%rax` is **less than** `0xfffffffffffff001` (i.e., not an error). * `jae 0x33`: If `%rax` is **greater than or equal to** `0xfffffffffffff001` (i.e., it is an error code), jump to `0x33`. * `ret`: If not an error, return normally.
3. **Error Handling (`0x33 - 0x3f`)**: * `mov 0xc8c09(%rip), %rcx`: Loads a pointer to the thread-local storage (TLS) area for the current thread. * `neg %eax`: Negates the error code (e.g., `-EFAULT` becomes `EFAULT`). * `mov %eax, %fs:(%rcx)`: Stores the positive errno value into the TLS area at the offset pointed to by `%rcx`. This is how glibc sets `errno`. * `rex.W`: This is likely the start of the next instruction (e.g., `mov` or `lea`) that was truncated.
### Key Observations
* **System Call**: `sys_getrandom` (number `0x31`). * **Error Handling**: The code explicitly checks for system call errors and sets `errno` via thread-local storage. * **Faulting Instruction**: The fault occurred at `0x2a` (`cmp $0xfffffffffff001, %rax`). This suggests that the `syscall` instruction itself may have caused a fault, or the comparison was executed with an invalid state. However, the `cmp` instruction itself is not typically faulting unless there's a deeper issue (e.g., invalid memory access in a preceding instruction, but here the fault is explicitly on the `cmp`).
### Possible Causes for the Fault
1. **Invalid System Call Number**: If `0x31` is not a valid system call on the target system, the `syscall` instruction might fault. 2. **Invalid Registers**: If the registers `%rdi`, `%rsi`, `%rdx` (arguments to `sys_getrandom`) contain invalid pointers, the kernel might fault when trying to access them. 3. **Kernel Bug**: A bug in the kernel's `sys_getrandom` implementation could cause a fault. 4. **Corrupted State**: The CPU state might be corrupted before the `syscall` instruction.
### Recommendations
1. **Check System Call Number**: Verify that `0x31` is the correct system call number for `sys_getrandom` on the target architecture and kernel version. 2. **Validate Arguments**: Ensure that the arguments passed to `sys_getrandom` (in `%rdi`, `%rsi`, `%rdx`) are valid pointers. 3. **Debugging**: Use a debugger to step through the code and inspect the state before the `syscall` instruction. 4. **Kernel Logs**: Check kernel logs (`dmesg`) for any error messages related to the system call.
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