linux-kernel - [PATCH 5.18 307/339] filemap: Cache the value of vm

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Message-Id: <20220613094936.069042805@linuxfoundation.org>
Date:   Mon, 13 Jun 2022 12:12:12 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        syzbot+5b96d55e5b54924c77ad@...kaller.appspotmail.com,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH 5.18 307/339] filemap: Cache the value of vm_flags

From: Matthew Wilcox (Oracle) <willy@...radead.org>

commit dcfa24ba68991ab69a48254a18377b45180ae664 upstream.

After we have unlocked the mmap_lock for I/O, the file is pinned, but
the VMA is not.  Checking this flag after that can be a use-after-free.
It's not a terribly interesting use-after-free as it can only read one
bit, and it's used to decide whether to read 2MB or 4MB.  But it
upsets the automated tools and it's generally bad practice anyway,
so let's fix it.

Reported-by: syzbot+5b96d55e5b54924c77ad@...kaller.appspotmail.com
Fixes: 4687fdbb805a ("mm/filemap: Support VM_HUGEPAGE for file mappings")
Cc: stable@...r.kernel.org
Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/filemap.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2991,11 +2991,12 @@ static struct file *do_sync_mmap_readahe
 	struct address_space *mapping = file->f_mapping;
 	DEFINE_READAHEAD(ractl, file, ra, mapping, vmf->pgoff);
 	struct file *fpin = NULL;
+	unsigned long vm_flags = vmf->vma->vm_flags;
 	unsigned int mmap_miss;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 	/* Use the readahead code, even if readahead is disabled */
-	if (vmf->vma->vm_flags & VM_HUGEPAGE) {
+	if (vm_flags & VM_HUGEPAGE) {
 		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 		ractl._index &= ~((unsigned long)HPAGE_PMD_NR - 1);
 		ra->size = HPAGE_PMD_NR;
@@ -3003,7 +3004,7 @@ static struct file *do_sync_mmap_readahe
 		 * Fetch two PMD folios, so we get the chance to actually
 		 * readahead, unless we've been told not to.
 		 */
-		if (!(vmf->vma->vm_flags & VM_RAND_READ))
+		if (!(vm_flags & VM_RAND_READ))
 			ra->size *= 2;
 		ra->async_size = HPAGE_PMD_NR;
 		page_cache_ra_order(&ractl, ra, HPAGE_PMD_ORDER);
@@ -3012,12 +3013,12 @@ static struct file *do_sync_mmap_readahe
 #endif
 
 	/* If we don't want any read-ahead, don't bother */
-	if (vmf->vma->vm_flags & VM_RAND_READ)
+	if (vm_flags & VM_RAND_READ)
 		return fpin;
 	if (!ra->ra_pages)
 		return fpin;
 
-	if (vmf->vma->vm_flags & VM_SEQ_READ) {
+	if (vm_flags & VM_SEQ_READ) {
 		fpin = maybe_unlock_mmap_for_io(vmf, fpin);
 		page_cache_sync_ra(&ractl, ra->ra_pages);
 		return fpin;