linux-kernel - Re: [syzbot] [mm?] kernel BUG in sg_init

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Date: Tue, 19 Mar 2024 11:27:15 +1300
From: Barry Song <21cnbao@...il.com>
To: syzbot+adbc983a1588b7805de3@...kaller.appspotmail.com
Cc: 21cnbao@...il.com,
	akpm@...ux-foundation.org,
	chengming.zhou@...ux.dev,
	hannes@...xchg.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	nphamcs@...il.com,
	syzkaller-bugs@...glegroups.com,
	yosryahmed@...gle.com
Subject: Re: [syzbot] [mm?] kernel BUG in sg_init_one

> syzbot has tested the proposed patch but the reproducer is still triggering an issue:
> WARNING in __kmap_to_page
> 
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 3529 at mm/highmem.c:167 __kmap_to_page+0x100/0x194 mm/highmem.c:167
> Modules linked in:
> Kernel panic - not syncing: kernel: panic_on_warn set ...
> 

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git e5eb28f6d1afebed4bb7d740a797d0390bd3a357

diff --git a/mm/zswap.c b/mm/zswap.c
index 9dec853647c8..17bf6d87b274 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1080,7 +1080,8 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
 	mutex_lock(&acomp_ctx->mutex);
 
 	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
-	if (acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) {
+	if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
+	    !virt_addr_valid(src)) {
 		memcpy(acomp_ctx->buffer, src, entry->length);
 		src = acomp_ctx->buffer;
 		zpool_unmap_handle(zpool, entry->handle);
@@ -1094,7 +1095,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
 	mutex_unlock(&acomp_ctx->mutex);
 
-	if (!acomp_ctx->is_sleepable || zpool_can_sleep_mapped(zpool))
+	if (src != acomp_ctx->buffer)
 		zpool_unmap_handle(zpool, entry->handle);
 }