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* [PATCH 6.1.y 1/2] erofs: handle overlapped pclusters out of crafted images properly
@ 2026-03-27  4:33 Gao Xiang
  2026-03-27  4:33 ` [PATCH 6.1.y 2/2] erofs: fix PSI memstall accounting Gao Xiang
  2026-04-08 13:30 ` Patch "erofs: handle overlapped pclusters out of crafted images properly" " gregkh
  0 siblings, 2 replies; 4+ messages in thread
From: Gao Xiang @ 2026-03-27  4:33 UTC (permalink / raw)
  To: stable, Greg Kroah-Hartman
  Cc: linux-erofs, Gao Xiang, syzbot+4fc98ed414ae63d1ada2,
	syzbot+de04e06b28cfecf2281c, syzbot+c8c8238b394be4a1087d,
	Alexey Panov

commit 9e2f9d34dd12e6e5b244ec488bcebd0c2d566c50 upstream.

syzbot reported a task hang issue due to a deadlock case where it is
waiting for the folio lock of a cached folio that will be used for
cache I/Os.

After looking into the crafted fuzzed image, I found it's formed with
several overlapped big pclusters as below:

 Ext:   logical offset   |  length :     physical offset    |  length
   0:        0..   16384 |   16384 :     151552..    167936 |   16384
   1:    16384..   32768 |   16384 :     155648..    172032 |   16384
   2:    32768..   49152 |   16384 :  537223168.. 537239552 |   16384
...

Here, extent 0/1 are physically overlapped although it's entirely
_impossible_ for normal filesystem images generated by mkfs.

First, managed folios containing compressed data will be marked as
up-to-date and then unlocked immediately (unlike in-place folios) when
compressed I/Os are complete.  If physical blocks are not submitted in
the incremental order, there should be separate BIOs to avoid dependency
issues.  However, the current code mis-arranges z_erofs_fill_bio_vec()
and BIO submission which causes unexpected BIO waits.

Second, managed folios will be connected to their own pclusters for
efficient inter-queries.  However, this is somewhat hard to implement
easily if overlapped big pclusters exist.  Again, these only appear in
fuzzed images so let's simply fall back to temporary short-lived pages
for correctness.

Additionally, it justifies that referenced managed folios cannot be
truncated for now and reverts part of commit 2080ca1ed3e4 ("erofs: tidy
up `struct z_erofs_bvec`") for simplicity although it shouldn't be any
difference.

[Alexey: This patch follows linux 6.6.y conflict resolution changes of
struct folio -> struct page]

Reported-by: syzbot+4fc98ed414ae63d1ada2@syzkaller.appspotmail.com
Reported-by: syzbot+de04e06b28cfecf2281c@syzkaller.appspotmail.com
Reported-by: syzbot+c8c8238b394be4a1087d@syzkaller.appspotmail.com
Tested-by: syzbot+4fc98ed414ae63d1ada2@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/r/0000000000002fda01061e334873@google.com
Fixes: 8e6c8fa9f2e9 ("erofs: enable big pcluster feature")
Link: https://lore.kernel.org/r/20240910070847.3356592-1-hsiangkao@linux.alibaba.com
Signed-off-by: Alexey Panov <apanov@astralinux.ru>
Link: https://lore.kernel.org/r/20250304110558.8315-2-apanov@astralinux.ru
Link: https://lore.kernel.org/r/20250304110558.8315-1-apanov@astralinux.ru
[ Gao Xiang: re-address the previous Alexey's backport. ]
CVE: CVE-2024-47736
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
 fs/erofs/zdata.c | 60 ++++++++++++++++++++++++++----------------------
 1 file changed, 32 insertions(+), 28 deletions(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5e6580217318..aa311aed0dd8 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1328,14 +1328,14 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
 		goto out;
 
 	lock_page(page);
-
-	/* only true if page reclaim goes wrong, should never happen */
-	DBG_BUGON(justfound && PagePrivate(page));
-
-	/* the page is still in manage cache */
-	if (page->mapping == mc) {
+	if (likely(page->mapping == mc)) {
 		WRITE_ONCE(pcl->compressed_bvecs[nr].page, page);
+		oldpage = page;
 
+		/*
+		 * The cached folio is still in managed cache but without
+		 * a valid `->private` pcluster hint.  Let's reconnect them.
+		 */
 		if (!PagePrivate(page)) {
 			/*
 			 * impossible to be !PagePrivate(page) for
@@ -1349,22 +1349,24 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
 			SetPagePrivate(page);
 		}
 
-		/* no need to submit io if it is already up-to-date */
-		if (PageUptodate(page)) {
-			unlock_page(page);
-			page = NULL;
+		if (likely(page->private == (unsigned long)pcl)) {
+			/* don't submit cache I/Os again if already uptodate */
+			if (PageUptodate(page)) {
+				unlock_page(page);
+				page = NULL;
+
+			}
+			goto out;
 		}
-		goto out;
+		/*
+		 * Already linked with another pcluster, which only appears in
+		 * crafted images by fuzzers for now.  But handle this anyway.
+		 */
+		tocache = false;	/* use temporary short-lived pages */
+	} else {
+		DBG_BUGON(1); /* referenced managed folios can't be truncated */
+		tocache = true;
 	}
-
-	/*
-	 * the managed page has been truncated, it's unsafe to
-	 * reuse this one, let's allocate a new cache-managed page.
-	 */
-	DBG_BUGON(page->mapping);
-	DBG_BUGON(!justfound);
-
-	tocache = true;
 	unlock_page(page);
 	put_page(page);
 out_allocpage:
@@ -1517,16 +1519,11 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
 		end = cur + pcl->pclusterpages;
 
 		do {
-			struct page *page;
-
-			page = pickup_page_for_submission(pcl, i++,
-					&f->pagepool, mc);
-			if (!page)
-				continue;
+			struct page *page = NULL;
 
 			if (bio && (cur != last_index + 1 ||
 				    last_bdev != mdev.m_bdev)) {
-submit_bio_retry:
+drain_io:
 				submit_bio(bio);
 				if (memstall) {
 					psi_memstall_leave(&pflags);
@@ -1535,6 +1532,13 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
 				bio = NULL;
 			}
 
+			if (!page) {
+				page = pickup_page_for_submission(pcl, i++,
+						&f->pagepool, mc);
+				if (!page)
+					continue;
+			}
+
 			if (unlikely(PageWorkingset(page)) && !memstall) {
 				psi_memstall_enter(&pflags);
 				memstall = 1;
@@ -1555,7 +1559,7 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
 			}
 
 			if (bio_add_page(bio, page, PAGE_SIZE, 0) < PAGE_SIZE)
-				goto submit_bio_retry;
+				goto drain_io;
 
 			last_index = cur;
 			bypass = false;
-- 
2.43.5



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Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
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2026-03-27  4:33 [PATCH 6.1.y 1/2] erofs: handle overlapped pclusters out of crafted images properly Gao Xiang
2026-03-27  4:33 ` [PATCH 6.1.y 2/2] erofs: fix PSI memstall accounting Gao Xiang
2026-04-08 13:30   ` Patch "erofs: fix PSI memstall accounting" has been added to the 6.1-stable tree gregkh
2026-04-08 13:30 ` Patch "erofs: handle overlapped pclusters out of crafted images properly" " gregkh

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