strparser: make sure __strp_recv isn't running before tearing down the parser

Overview

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

strparser: make sure __strp_recv isn't running before tearing down the parser

The comment above strp_done() claims that if strp is stopped, strp_recv will no longer be called. That's only true if the caller has a mechanism (eg locking) to guarantee that strp_recv() calls that started before strp_stop() have completed by the time we call strp_done().

This adds a dummy lock_sock/release_sock pair to guarantee that any in-flight strp_recv() (which runs under either bh_lock_sock or lock_sock, depending if it's called from ->sk_data_ready or strp_work) has completed.

Only espintcp can be affected by this race condition, but this patch makes sure no future user of strp can have the bug.

This could crash on strp->sk ("general mode" of strp), but this mode has been here for 9 years and has never been used. It'll be gone soon, no point worrying about it.

Switch the stopped/paused/etc bits to u8's to avoid races between strp_stop() and strp_pause/unpause().

A reproducer has been published and turns the possible UAF into an exploit [1].

Affected

• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < a18dd388045dc7263d99a07db9de4e0f149ca8f1
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 9f3e9fe1b155e9b4572054d8d140586bc3512ecf
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < d2b5f637b9b67a79a50d42614d10653c13b4e449
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < eaa3a29004c063d7e9d5ea55636f693f67e6db0f
• Linux >= e27cca96cd68fa2c6814c90f9a1cfd36bb68c593 < 0984ebc631792acf8fff105112ee74a6b8f1efcc
• Linux 5.6

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.