Description
In the Linux kernel, the following vulnerability has been resolved: userfaultfd: gate must_wait writability check on pte_present() userfaultfd_must_wait() and userfaultfd_huge_must_wait() read the PTE without taking the page table lock and then apply pte_write() / huge_pte_write() to it. Those accessors decode bits from the present encoding only; on a swap or migration entry they read the offset bits that happen to share the same position and return an undefined result. The intent of the check is "is this fault still WP-blocked?". A non-marker swap entry means the page is in transit -- the userfault context the original fault delivered against is no longer the same, and the swap-in or migration completion path will re-deliver a fresh fault if userspace still needs to handle it. Worst case under the current code the garbage write bit says "wait", and the thread stays asleep until a UFFDIO_WAKE that may never arrive. Gate the writability check on pte_present() so the lockless re-check only inspects present-PTE bits when the entry is actually present. The non-present, non-marker case returns "don't wait" and lets the fault path retry.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
Linux Linux
Default version status: unaffected
369cd2121be440543280b91056de187f625d0dbb to < a5700a4c1c9099ac2ac73fe8a09cf059972e0d2faffected369cd2121be440543280b91056de187f625d0dbb to < d4026417e8184d13850a0bad4d96ceb6ed9f7152affected369cd2121be440543280b91056de187f625d0dbb to < 29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0affected369cd2121be440543280b91056de187f625d0dbb to < 5f4dbdb0a87596214076b20b94f2b71b522170b3affected369cd2121be440543280b91056de187f625d0dbb to < a6e9a4939e359599701b1da351e84f72e021443aaffected369cd2121be440543280b91056de187f625d0dbb to < 60d696a037eeeedfb57756dfe7ec08a1587c8631affected369cd2121be440543280b91056de187f625d0dbb to < 710183888174639a15fcec16cd1af766b8480bb7affected369cd2121be440543280b91056de187f625d0dbb to < 8e80af52db652fbc41320eee45a4f73bc029faf2affected
Linux Linux
Default version status: affected
4.11affected0 to < 4.11unaffected5.10.261 to ≤ 5.10.*unaffected5.15.212 to ≤ 5.15.*unaffected6.1.178 to ≤ 6.1.*unaffected6.6.145 to ≤ 6.6.*unaffected6.12.96 to ≤ 6.12.*unaffected6.18.39 to ≤ 6.18.*unaffected7.1.4 to ≤ 7.1.*unaffected7.2 to ≤ *unaffected
References
- https://git.kernel.org/stable/c/a5700a4c1c9099ac2ac73fe8a09cf059972e0d2f ↗
- https://git.kernel.org/stable/c/d4026417e8184d13850a0bad4d96ceb6ed9f7152 ↗
- https://git.kernel.org/stable/c/29e6f952c5fb7dc1d6b90fe5b7f36063d44ddae0 ↗
- https://git.kernel.org/stable/c/5f4dbdb0a87596214076b20b94f2b71b522170b3 ↗
- https://git.kernel.org/stable/c/a6e9a4939e359599701b1da351e84f72e021443a ↗
- https://git.kernel.org/stable/c/60d696a037eeeedfb57756dfe7ec08a1587c8631 ↗
- https://git.kernel.org/stable/c/710183888174639a15fcec16cd1af766b8480bb7 ↗
- https://git.kernel.org/stable/c/8e80af52db652fbc41320eee45a4f73bc029faf2 ↗