| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2022-49052: mm: fix unexpected zeroed page mapping with zram swap |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| mm: fix unexpected zeroed page mapping with zram swap |
| |
| Two processes under CLONE_VM cloning, user process can be corrupted by |
| seeing zeroed page unexpectedly. |
| |
| CPU A CPU B |
| |
| do_swap_page do_swap_page |
| SWP_SYNCHRONOUS_IO path SWP_SYNCHRONOUS_IO path |
| swap_readpage valid data |
| swap_slot_free_notify |
| delete zram entry |
| swap_readpage zeroed(invalid) data |
| pte_lock |
| map the *zero data* to userspace |
| pte_unlock |
| pte_lock |
| if (!pte_same) |
| goto out_nomap; |
| pte_unlock |
| return and next refault will |
| read zeroed data |
| |
| The swap_slot_free_notify is bogus for CLONE_VM case since it doesn't |
| increase the refcount of swap slot at copy_mm so it couldn't catch up |
| whether it's safe or not to discard data from backing device. In the |
| case, only the lock it could rely on to synchronize swap slot freeing is |
| page table lock. Thus, this patch gets rid of the swap_slot_free_notify |
| function. With this patch, CPU A will see correct data. |
| |
| CPU A CPU B |
| |
| do_swap_page do_swap_page |
| SWP_SYNCHRONOUS_IO path SWP_SYNCHRONOUS_IO path |
| swap_readpage original data |
| pte_lock |
| map the original data |
| swap_free |
| swap_range_free |
| bd_disk->fops->swap_slot_free_notify |
| swap_readpage read zeroed data |
| pte_unlock |
| pte_lock |
| if (!pte_same) |
| goto out_nomap; |
| pte_unlock |
| return |
| on next refault will see mapped data by CPU B |
| |
| The concern of the patch would increase memory consumption since it |
| could keep wasted memory with compressed form in zram as well as |
| uncompressed form in address space. However, most of cases of zram uses |
| no readahead and do_swap_page is followed by swap_free so it will free |
| the compressed form from in zram quickly. |
| |
| The Linux kernel CVE team has assigned CVE-2022-49052 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 4.19.242 with commit f86d55cf616199404c05f5b0c5c41b17351baa02 |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.4.193 with commit f098f8b9820fe3f2e41aefc4329dfe8a3859d1c1 |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.10.112 with commit 20ed94f8181a25212e7404e44958e234f407624b |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.15.35 with commit 12ba1d38115a101c45d8e0ca3aa1181fd148e57f |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.17.4 with commit afac4b88699a06c8b9369f9d759a1ec3c254b788 |
| Issue introduced in 4.15 with commit 0bcac06f27d7528591c27ac2b093ccd71c5d0168 and fixed in 5.18 with commit e914d8f00391520ecc4495dd0ca0124538ab7119 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2022-49052 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| mm/page_io.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/f86d55cf616199404c05f5b0c5c41b17351baa02 |
| https://git.kernel.org/stable/c/f098f8b9820fe3f2e41aefc4329dfe8a3859d1c1 |
| https://git.kernel.org/stable/c/20ed94f8181a25212e7404e44958e234f407624b |
| https://git.kernel.org/stable/c/12ba1d38115a101c45d8e0ca3aa1181fd148e57f |
| https://git.kernel.org/stable/c/afac4b88699a06c8b9369f9d759a1ec3c254b788 |
| https://git.kernel.org/stable/c/e914d8f00391520ecc4495dd0ca0124538ab7119 |
