From: Yosry Ahmed <yosry.ahmed@linux.dev> mainline inclusion from mainline-v6.15-rc1 commit c11bcbc0a517acf69282c8225059b2a8ac5fe628 category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBLDIU CVE: CVE-2025-21693 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i... -------------------------------- Currently, zswap_cpu_comp_dead() calls crypto_free_acomp() while holding the per-CPU acomp_ctx mutex. crypto_free_acomp() then holds scomp_lock (through crypto_exit_scomp_ops_async()). On the other hand, crypto_alloc_acomp_node() holds the scomp_lock (through crypto_scomp_init_tfm()), and then allocates memory. If the allocation results in reclaim, we may attempt to hold the per-CPU acomp_ctx mutex. The above dependencies can cause an ABBA deadlock. For example in the following scenario: (1) Task A running on CPU #1: crypto_alloc_acomp_node() Holds scomp_lock Enters reclaim Reads per_cpu_ptr(pool->acomp_ctx, 1) (2) Task A is descheduled (3) CPU #1 goes offline zswap_cpu_comp_dead(CPU #1) Holds per_cpu_ptr(pool->acomp_ctx, 1)) Calls crypto_free_acomp() Waits for scomp_lock (4) Task A running on CPU #2: Waits for per_cpu_ptr(pool->acomp_ctx, 1) // Read on CPU #1 DEADLOCK Since there is no requirement to call crypto_free_acomp() with the per-CPU acomp_ctx mutex held in zswap_cpu_comp_dead(), move it after the mutex is unlocked. Also move the acomp_request_free() and kfree() calls for consistency and to avoid any potential sublte locking dependencies in the future. With this, only setting acomp_ctx fields to NULL occurs with the mutex held. This is similar to how zswap_cpu_comp_prepare() only initializes acomp_ctx fields with the mutex held, after performing all allocations before holding the mutex. Opportunistically, move the NULL check on acomp_ctx so that it takes place before the mutex dereference. Link: https://lkml.kernel.org/r/20250226185625.2672936-1-yosry.ahmed@linux.dev Fixes: 12dcb0ef5406 ("mm: zswap: properly synchronize freeing resources during CPU hotunplug") Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Co-developed-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev> Reported-by: syzbot+1a517ccfcbc6a7ab0f82@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/67bcea51.050a0220.bbfd1.0096.GAE@google.com/ Acked-by: Herbert Xu <herbert@gondor.apana.org.au> Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev> Reviewed-by: Nhat Pham <nphamcs@gmail.com> Tested-by: Nhat Pham <nphamcs@gmail.com> Cc: David S. Miller <davem@davemloft.net> Cc: Eric Biggers <ebiggers@kernel.org> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Chris Murphy <lists@colorremedies.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Conflicts: mm/zswap.c [Wupeng Ma: context conflicts] Signed-off-by: Wupeng Ma <mawupeng1@huawei.com> --- mm/zswap.c | 30 ++++++++++++++++++++++-------- 1 file changed, 22 insertions(+), 8 deletions(-) diff --git a/mm/zswap.c b/mm/zswap.c index 8f7a8aa6d439e..d0984b103eb81 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -512,18 +512,32 @@ static int zswap_cpu_comp_dead(unsigned int cpu, struct hlist_node *node) { struct zswap_pool *pool = hlist_entry(node, struct zswap_pool, node); struct crypto_acomp_ctx *acomp_ctx = per_cpu_ptr(pool->acomp_ctx, cpu); + struct acomp_req *req; + struct crypto_acomp *acomp; + u8 *buffer; + + if (IS_ERR_OR_NULL(acomp_ctx)) + return 0; mutex_lock(&acomp_ctx->mutex); - if (!IS_ERR_OR_NULL(acomp_ctx)) { - if (!IS_ERR_OR_NULL(acomp_ctx->req)) - acomp_request_free(acomp_ctx->req); - acomp_ctx->req = NULL; - if (!IS_ERR_OR_NULL(acomp_ctx->acomp)) - crypto_free_acomp(acomp_ctx->acomp); - kfree(acomp_ctx->buffer); - } + req = acomp_ctx->req; + acomp = acomp_ctx->acomp; + buffer = acomp_ctx->buffer; + acomp_ctx->req = NULL; + acomp_ctx->acomp = NULL; + acomp_ctx->buffer = NULL; mutex_unlock(&acomp_ctx->mutex); + /* + * Do the actual freeing after releasing the mutex to avoid subtle + * locking dependencies causing deadlocks. + */ + if (!IS_ERR_OR_NULL(req)) + acomp_request_free(req); + if (!IS_ERR_OR_NULL(acomp)) + crypto_free_acomp(acomp); + kfree(buffer); + return 0; } -- 2.43.0