linux-kernel - [PATCH] Squashfs: don't call kmalloc in decompressors

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Message-Id: <20220822215430.15933-1-phillip@squashfs.org.uk>
Date:   Mon, 22 Aug 2022 22:54:30 +0100
From:   Phillip Lougher <phillip@...ashfs.org.uk>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        akpm@...ux-foundation.org,
        Phillip Lougher <phillip@...ashfs.org.uk>,
        Chris Murphy <lists@...orremedies.com>
Subject: [PATCH] Squashfs: don't call kmalloc in decompressors

The decompressors may be called while in an atomic section.
So move the kmalloc() out of this path, and into the "page actor"
init function.

This fixes a regression introduced by commit
f268eedddf35 ("squashfs: extend "page actor" to handle missing pages")

Reported-by: Chris Murphy <lists@...orremedies.com>
Signed-off-by: Phillip Lougher <phillip@...ashfs.org.uk>
---
 fs/squashfs/file.c        |  2 +-
 fs/squashfs/file_direct.c |  2 +-
 fs/squashfs/page_actor.c  | 34 +++++++++++++++-------------------
 fs/squashfs/page_actor.h  |  5 +++++
 4 files changed, 22 insertions(+), 21 deletions(-)

diff --git a/fs/squashfs/file.c b/fs/squashfs/file.c
index 98e64fec75b7..e56510964b22 100644
--- a/fs/squashfs/file.c
+++ b/fs/squashfs/file.c
@@ -593,7 +593,7 @@ static void squashfs_readahead(struct readahead_control *ractl)
 
 		res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
 
-		kfree(actor);
+		squashfs_page_actor_free(actor);
 
 		if (res == expected) {
 			int bytes;
diff --git a/fs/squashfs/file_direct.c b/fs/squashfs/file_direct.c
index be4b12d31e0c..f1ccad519e28 100644
--- a/fs/squashfs/file_direct.c
+++ b/fs/squashfs/file_direct.c
@@ -74,7 +74,7 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
 	/* Decompress directly into the page cache buffers */
 	res = squashfs_read_data(inode->i_sb, block, bsize, NULL, actor);
 
-	kfree(actor);
+	squashfs_page_actor_free(actor);
 
 	if (res < 0)
 		goto mark_errored;
diff --git a/fs/squashfs/page_actor.c b/fs/squashfs/page_actor.c
index b23b780d8f42..54b93bf4a25c 100644
--- a/fs/squashfs/page_actor.c
+++ b/fs/squashfs/page_actor.c
@@ -52,6 +52,7 @@ struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
 	actor->buffer = buffer;
 	actor->pages = pages;
 	actor->next_page = 0;
+	actor->tmp_buffer = NULL;
 	actor->squashfs_first_page = cache_first_page;
 	actor->squashfs_next_page = cache_next_page;
 	actor->squashfs_finish_page = cache_finish_page;
@@ -68,20 +69,9 @@ static void *handle_next_page(struct squashfs_page_actor *actor)
 
 	if ((actor->next_page == actor->pages) ||
 			(actor->next_index != actor->page[actor->next_page]->index)) {
-		if (actor->alloc_buffer) {
-			void *tmp_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
-
-			if (tmp_buffer) {
-				actor->tmp_buffer = tmp_buffer;
-				actor->next_index++;
-				actor->returned_pages++;
-				return tmp_buffer;
-			}
-		}
-
 		actor->next_index++;
 		actor->returned_pages++;
-		return ERR_PTR(-ENOMEM);
+		return actor->alloc_buffer ? actor->tmp_buffer : ERR_PTR(-ENOMEM);
 	}
 
 	actor->next_index++;
@@ -96,11 +86,10 @@ static void *direct_first_page(struct squashfs_page_actor *actor)
 
 static void *direct_next_page(struct squashfs_page_actor *actor)
 {
-	if (actor->pageaddr)
+	if (actor->pageaddr) {
 		kunmap_local(actor->pageaddr);
-
-	kfree(actor->tmp_buffer);
-	actor->pageaddr = actor->tmp_buffer = NULL;
+		actor->pageaddr = NULL;
+	}
 
 	return handle_next_page(actor);
 }
@@ -109,8 +98,6 @@ static void direct_finish_page(struct squashfs_page_actor *actor)
 {
 	if (actor->pageaddr)
 		kunmap_local(actor->pageaddr);
-
-	kfree(actor->tmp_buffer);
 }
 
 struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_info *msblk,
@@ -121,6 +108,16 @@ struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_
 	if (actor == NULL)
 		return NULL;
 
+	if (msblk->decompressor->alloc_buffer) {
+		actor->tmp_buffer = kmalloc(PAGE_SIZE, GFP_KERNEL);
+
+		if (actor->tmp_buffer == NULL) {
+			kfree(actor);
+			return NULL;
+		}
+	} else
+		actor->tmp_buffer = NULL;
+
 	actor->length = length ? : pages * PAGE_SIZE;
 	actor->page = page;
 	actor->pages = pages;
@@ -128,7 +125,6 @@ struct squashfs_page_actor *squashfs_page_actor_init_special(struct squashfs_sb_
 	actor->returned_pages = 0;
 	actor->next_index = page[0]->index & ~((1 << (msblk->block_log - PAGE_SHIFT)) - 1);
 	actor->pageaddr = NULL;
-	actor->tmp_buffer = NULL;
 	actor->alloc_buffer = msblk->decompressor->alloc_buffer;
 	actor->squashfs_first_page = direct_first_page;
 	actor->squashfs_next_page = direct_next_page;
diff --git a/fs/squashfs/page_actor.h b/fs/squashfs/page_actor.h
index 24841d28bc0f..95ffbb543d91 100644
--- a/fs/squashfs/page_actor.h
+++ b/fs/squashfs/page_actor.h
@@ -29,6 +29,11 @@ extern struct squashfs_page_actor *squashfs_page_actor_init(void **buffer,
 extern struct squashfs_page_actor *squashfs_page_actor_init_special(
 				struct squashfs_sb_info *msblk,
 				struct page **page, int pages, int length);
+static inline void squashfs_page_actor_free(struct squashfs_page_actor *actor)
+{
+	kfree(actor->tmp_buffer);
+	kfree(actor);
+}
 static inline void *squashfs_first_page(struct squashfs_page_actor *actor)
 {
 	return actor->squashfs_first_page(actor);
-- 
2.35.1