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Message-ID: <2024022824-CVE-2021-46984-e55e@gregkh> Date: Wed, 28 Feb 2024 09:14:34 +0100 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-cve-announce@...r.kernel.org Cc: gregkh@...nel.org Subject: CVE-2021-46984: kyber: fix out of bounds access when preempted From: gregkh@...nel.org Description =========== In the Linux kernel, the following vulnerability has been resolved: kyber: fix out of bounds access when preempted __blk_mq_sched_bio_merge() gets the ctx and hctx for the current CPU and passes the hctx to ->bio_merge(). kyber_bio_merge() then gets the ctx for the current CPU again and uses that to get the corresponding Kyber context in the passed hctx. However, the thread may be preempted between the two calls to blk_mq_get_ctx(), and the ctx returned the second time may no longer correspond to the passed hctx. This "works" accidentally most of the time, but it can cause us to read garbage if the second ctx came from an hctx with more ctx's than the first one (i.e., if ctx->index_hw[hctx->type] > hctx->nr_ctx). This manifested as this UBSAN array index out of bounds error reported by Jakub: UBSAN: array-index-out-of-bounds in ../kernel/locking/qspinlock.c:130:9 index 13106 is out of range for type 'long unsigned int [128]' Call Trace: dump_stack+0xa4/0xe5 ubsan_epilogue+0x5/0x40 __ubsan_handle_out_of_bounds.cold.13+0x2a/0x34 queued_spin_lock_slowpath+0x476/0x480 do_raw_spin_lock+0x1c2/0x1d0 kyber_bio_merge+0x112/0x180 blk_mq_submit_bio+0x1f5/0x1100 submit_bio_noacct+0x7b0/0x870 submit_bio+0xc2/0x3a0 btrfs_map_bio+0x4f0/0x9d0 btrfs_submit_data_bio+0x24e/0x310 submit_one_bio+0x7f/0xb0 submit_extent_page+0xc4/0x440 __extent_writepage_io+0x2b8/0x5e0 __extent_writepage+0x28d/0x6e0 extent_write_cache_pages+0x4d7/0x7a0 extent_writepages+0xa2/0x110 do_writepages+0x8f/0x180 __writeback_single_inode+0x99/0x7f0 writeback_sb_inodes+0x34e/0x790 __writeback_inodes_wb+0x9e/0x120 wb_writeback+0x4d2/0x660 wb_workfn+0x64d/0xa10 process_one_work+0x53a/0xa80 worker_thread+0x69/0x5b0 kthread+0x20b/0x240 ret_from_fork+0x1f/0x30 Only Kyber uses the hctx, so fix it by passing the request_queue to ->bio_merge() instead. BFQ and mq-deadline just use that, and Kyber can map the queues itself to avoid the mismatch. The Linux kernel CVE team has assigned CVE-2021-46984 to this issue. Affected and fixed versions =========================== Issue introduced in 4.18 with commit a6088845c2bf and fixed in 5.4.120 with commit 0b6b4b90b74c Issue introduced in 4.18 with commit a6088845c2bf and fixed in 5.10.38 with commit 54dbe2d2c1fc Issue introduced in 4.18 with commit a6088845c2bf and fixed in 5.11.22 with commit a287cd84e047 Issue introduced in 4.18 with commit a6088845c2bf and fixed in 5.12.5 with commit 2ef3c76540c4 Issue introduced in 4.18 with commit a6088845c2bf and fixed in 5.13 with commit efed9a3337e3 Please see https://www.kernel.org or 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-2021-46984 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: block/bfq-iosched.c block/blk-mq-sched.c block/kyber-iosched.c block/mq-deadline.c include/linux/elevator.h 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/0b6b4b90b74c27bea968c214d820ba4254b903a5 https://git.kernel.org/stable/c/54dbe2d2c1fcabf650c7a8b747601da355cd7f9f https://git.kernel.org/stable/c/a287cd84e047045f5a4d4da793414e848de627c6 https://git.kernel.org/stable/c/2ef3c76540c49167a0bc3d5f80d00fd1fc4586df https://git.kernel.org/stable/c/efed9a3337e341bd0989161b97453b52567bc59d
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