[PATCH v2 07/16] btrfs: send: Proactively round up to kmalloc bucket size

[Kees Cook]

Instead of discovering the kmalloc bucket size _after_ allocation, round
up proactively so the allocation is explicitly made for the full size,
allowing the compiler to correctly reason about the resulting size of
the buffer through the existing __alloc_size() hint.

Cc: Chris Mason <clm@xxxxxx>
Cc: Josef Bacik <josef@xxxxxxxxxxxxxx>
Cc: linux-btrfs@xxxxxxxxxxxxxxx
Acked-by: David Sterba <dsterba@xxxxxxxx>
Link: https://lore.kernel.org/lkml/20220922133014.GI32411@xxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/btrfs/send.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/send.c b/fs/btrfs/send.c
index e7671afcee4f..d40d65598e8f 100644
--- a/fs/btrfs/send.c
+++ b/fs/btrfs/send.c
@@ -435,6 +435,11 @@ static int fs_path_ensure_buf(struct fs_path *p, int len)
 	path_len = p->end - p->start;
 	old_buf_len = p->buf_len;
 
+	/*
+	 * Allocate to the next largest kmalloc bucket size, to let
+	 * the fast path happen most of the time.
+	 */
+	len = kmalloc_size_roundup(len);
 	/*
 	 * First time the inline_buf does not suffice
 	 */
@@ -448,11 +453,7 @@ static int fs_path_ensure_buf(struct fs_path *p, int len)
 	if (!tmp_buf)
 		return -ENOMEM;
 	p->buf = tmp_buf;
-	/*
-	 * The real size of the buffer is bigger, this will let the fast path
-	 * happen most of the time
-	 */
-	p->buf_len = ksize(p->buf);
+	p->buf_len = len;
 
 	if (p->reversed) {
 		tmp_buf = p->buf + old_buf_len - path_len - 1;
-- 
2.34.1