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
f268eedd ("squashfs: extend "page actor" to handle missing pages")

Link: https://lkml.kernel.org/r/20220822215430.15933-1-phillip@squashfs.org.uk
Fixes: f268eedd ("squashfs: extend "page actor" to handle missing pages")
Reported-by: Chris Murphy <lists@colorremedies.com>
Signed-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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;

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;

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;

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);