FAILED: patch "[PATCH] zram: fix out-of-bounds access in writeback_store()" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x 894913e2d35c46ff19a77530907771ae57862b96
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026090306-quartered-glade-f172@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 894913e2d35c46ff19a77530907771ae57862b96 Mon Sep 17 00:00:00 2001
From: Longlong Xia <[email protected]>
Date: Tue, 4 Aug 2026 14:59:18 +0800
Subject: [PATCH] zram: fix out-of-bounds access in writeback_store()

Patch series "zram: fix stale scan bounds after reinitialization".

Both writeback_store() and read_block_state() derive their table scan bounds from zram->disksize before acquiring dev_lock. If the device is reset and reinitialized with a smaller disksize between that read and lock acquisition, the bound can describe the old table while the scan operates on the new one. This can lead to out-of-bounds slot accesses.

Move both bound calculations under dev_lock so each bound remains consistent with the table throughout its scan. Keep the fixes separate because the affected interfaces originate from different commits and can be backported independently.

This patch (of 2):

writeback_store() calculates the table scan bounds before taking dev_lock. A reset followed by reconfiguration with a smaller disksize can therefore replace zram->table while writeback_store() is waiting for the lock. Once it acquires the lock, it sees an initialized device but scans the new table using the old upper bound, resulting in an out-of-bounds access.

Calculate the number of pages while holding dev_lock so the scan bound matches the table protected by the lock.

index 56183c827e1b..2be5c20e3f14 100644
@@ -1235,8 +1235,8 @@ static ssize_t writeback_store(struct device *dev,
 			       const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
-	u64 nr_pages = zram->disksize >> PAGE_SHIFT;
-	unsigned long lo = 0, hi = nr_pages;
+	u64 nr_pages;
+	unsigned long lo = 0, hi;
 	struct zram_pp_ctl *pp_ctl = NULL;
 	struct zram_wb_ctl *wb_ctl = NULL;
 	char *args, *param, *val;

@@ -1250,6 +1250,9 @@ static ssize_t writeback_store(struct device *dev,
 	if (!zram->backing_dev)
 		return -ENODEV;
 
+	nr_pages = zram->disksize >> PAGE_SHIFT;
+	hi = nr_pages;
+
 	pp_ctl = init_pp_ctl();
 	if (!pp_ctl)
 		return -ENOMEM;

From: Longlong Xia <[email protected]>

[ Upstream commit 894913e2d35c46ff19a77530907771ae57862b96 ]

Patch series "zram: fix stale scan bounds after reinitialization".

Both writeback_store() and read_block_state() derive their table scan bounds from zram->disksize before acquiring dev_lock. If the device is reset and reinitialized with a smaller disksize between that read and lock acquisition, the bound can describe the old table while the scan operates on the new one. This can lead to out-of-bounds slot accesses.

Move both bound calculations under dev_lock so each bound remains consistent with the table throughout its scan. Keep the fixes separate because the affected interfaces originate from different commits and can be backported independently.

This patch (of 2):

writeback_store() calculates the table scan bounds before taking dev_lock. A reset followed by reconfiguration with a smaller disksize can therefore replace zram->table while writeback_store() is waiting for the lock. Once it acquires the lock, it sees an initialized device but scans the new table using the old upper bound, resulting in an out-of-bounds access.

Calculate the number of pages while holding dev_lock so the scan bound matches the table protected by the lock.

---
 drivers/block/zram/zram_drv.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

index a9f71b27d235a..464800ea61768 100644
@@ -627,7 +627,7 @@ static ssize_t writeback_store(struct device *dev,
 		struct device_attribute *attr, const char *buf, size_t len)
 {
 	struct zram *zram = dev_to_zram(dev);
-	unsigned long nr_pages = zram->disksize >> PAGE_SHIFT;
+	unsigned long nr_pages;
 	unsigned long index = 0;
 	struct bio bio;
 	struct bio_vec bio_vec;

@@ -644,11 +644,9 @@ static ssize_t writeback_store(struct device *dev,
 		if (strncmp(buf, PAGE_WB_SIG, sizeof(PAGE_WB_SIG) - 1))
 			return -EINVAL;
 
-		if (kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index) ||
-				index >= nr_pages)
+		if (kstrtol(buf + sizeof(PAGE_WB_SIG) - 1, 10, &index))
 			return -EINVAL;
 
-		nr_pages = 1;
 		mode = PAGE_WRITEBACK;
 	}
 

@@ -663,6 +661,15 @@ static ssize_t writeback_store(struct device *dev,
 		goto release_init_lock;
 	}
 
+	nr_pages = zram->disksize >> PAGE_SHIFT;
+	if (mode == PAGE_WRITEBACK) {
+		if (index >= nr_pages) {
+			ret = -EINVAL;
+			goto release_init_lock;
+		}
+		nr_pages = 1;
+	}
+
 	page = alloc_page(GFP_KERNEL);
 	if (!page) {
 		ret = -ENOMEM;

2.53.0