+ mm-shmem-reject-page-aligned-fallocate-end-overflow.patch added to mm-new branch

The patch titled
     Subject: mm: shmem: reject page-aligned fallocate end overflow
has been added to the -mm mm-new branch.  Its filename is
     mm-shmem-reject-page-aligned-fallocate-end-overflow.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-shmem-reject-page-aligned-fallocate-end-overflow.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

The mm-new branch of mm.git is not included in linux-next

If a few days of testing in mm-new is successful, the patch will me moved
into mm.git's mm-unstable branch, which is included in linux-next

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------------------------------------------------------
From: Zhiling Zou <[email protected]>
Subject: mm: shmem: reject page-aligned fallocate end overflow
Date: Fri, 31 Jul 2026 11:22:51 +0800

shmem_fallocate() validates offset + len with inode_newsize_ok(), but then
rounds that end offset up to a page boundary before entering the
preallocation loop.

For a valid request ending at MAX_LFS_FILESIZE, such as offset = 0 and len
= LLONG_MAX, adding PAGE_SIZE - 1 to the validated end can overflow the
signed loff_t used for the rounded end calculation.  If that wrapped value
is then converted into a page index, shmem_fallocate() can enter the folio
allocation loop with an invalid range.

Use check_add_overflow() when calculating the page-aligned end, and fail
before entering the allocation loop if the rounded end cannot be
represented.

Link: https://lore.kernel.org/1929a466735dcbb9438936ff50b7a4fc2332a8a4.1785377919.git.zhilinz@nebusec.ai
Fixes: e2d12e22c59c ("tmpfs: support fallocate preallocation")
Signed-off-by: Zhiling Zou <[email protected]>
Reported-by: Vega <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 mm/shmem.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

--- a/mm/shmem.c~mm-shmem-reject-page-aligned-fallocate-end-overflow
+++ a/mm/shmem.c
@@ -3627,6 +3627,7 @@ static long shmem_fallocate(struct file
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_falloc shmem_falloc;
 	pgoff_t start, index, end, undo_fallocend;
+	loff_t aligned_end;
 	int error;
 
 	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
@@ -3683,8 +3684,15 @@ static long shmem_fallocate(struct file
 		goto out;
 	}
 
+	/* Check for wraparound */
+	if (check_add_overflow(offset + len, (loff_t)PAGE_SIZE - 1,
+			       &aligned_end)) {
+		error = -EFBIG;
+		goto out;
+	}
+
 	start = offset >> PAGE_SHIFT;
-	end = (offset + len + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	end = aligned_end >> PAGE_SHIFT;
 	/* Try to avoid a swapstorm if len is impossible to satisfy */
 	if (sbinfo->max_blocks && end - start > sbinfo->max_blocks) {
 		error = -ENOSPC;
_

Patches currently in -mm which might be from [email protected] are

mm-page_table_check-skip-special-zero-mappings.patch
mm-shmem-reject-page-aligned-fallocate-end-overflow.patch