CVE-2021-47527

In the Linux kernel, the following vulnerability has been resolved:

serial: core: fix transmit-buffer reset and memleak

Commit 761ed4a94582 (tty: serial_core: convert uart_close to use tty_port_close) converted serial core to use tty_port_close() but failed to notice that the transmit buffer still needs to be freed on final close.

Not freeing the transmit buffer means that the buffer is no longer cleared on next open so that any ioctl() waiting for the buffer to drain might wait indefinitely (e.g. on termios changes) or that stale data can end up being transmitted in case tx is restarted.

Furthermore, the buffer of any port that has been opened would leak on driver unbind.

Note that the port lock is held when clearing the buffer pointer due to the ldisc race worked around by commit a5ba1d95e46e (uart: fix race between uart_put_char() and uart_shutdown()).

Also note that the tty-port shutdown() callback is not called for console ports so it is not strictly necessary to free the buffer page after releasing the lock (cf. d72402145ace (tty/serial: do not free trasnmit buffer page under port lock)).

Weakness

The product does not sufficiently track and release allocated memory after it has been used, making the memory unavailable for reallocation and reuse.

Affected Software

Potential Mitigations

• Choose a language or tool that provides automatic memory management, or makes manual memory management less error-prone.
• For example, glibc in Linux provides protection against free of invalid pointers.
• When using Xcode to target OS X or iOS, enable automatic reference counting (ARC) [REF-391].
• To help correctly and consistently manage memory when programming in C++, consider using a smart pointer class such as std::auto_ptr (defined by ISO/IEC ISO/IEC 14882:2003), std::shared_ptr and std::unique_ptr (specified by an upcoming revision of the C++ standard, informally referred to as C++ 1x), or equivalent solutions such as Boost.

References

• https://git.kernel.org/stable/c/00de977f9e0aa9760d9a79d1e41ff780f74e3424
• https://git.kernel.org/stable/c/011f6c92b5bf6e1fbfdedc8b5232f64c1c493206
• https://git.kernel.org/stable/c/1179b168fa3f3a6aae3bd140000455a0e58457db
• https://git.kernel.org/stable/c/64e491c1634b73d3bddc081d08620bdc92ab2c12
• https://git.kernel.org/stable/c/c5da8aa441053958594f94254592bb41264bdfbf
• https://git.kernel.org/stable/c/e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f
• https://git.kernel.org/stable/c/e74d9663fd57640fc3394abb5c76fa95b9cc2f2e
• https://git.kernel.org/stable/c/00de977f9e0aa9760d9a79d1e41ff780f74e3424
• https://git.kernel.org/stable/c/011f6c92b5bf6e1fbfdedc8b5232f64c1c493206
• https://git.kernel.org/stable/c/1179b168fa3f3a6aae3bd140000455a0e58457db
• https://git.kernel.org/stable/c/64e491c1634b73d3bddc081d08620bdc92ab2c12
• https://git.kernel.org/stable/c/c5da8aa441053958594f94254592bb41264bdfbf
• https://git.kernel.org/stable/c/e1722acf4f0d4d67b60f57e08ce16f8b66cd4b8f
• https://git.kernel.org/stable/c/e74d9663fd57640fc3394abb5c76fa95b9cc2f2e