From 118cf3f55975352ac357fb194405031458186819 Mon Sep 17 00:00:00 2001 From: "Christian A. Ehrhardt" Date: Thu, 26 Mar 2026 22:49:02 +0100 Subject: [PATCH] lib/scatterlist: fix temp buffer in extract_user_to_sg() Instead of allocating a temporary buffer for extracted user pages extract_user_to_sg() uses the end of the to be filled scatterlist as a temporary buffer. Fix the calculation of the start address if the scatterlist already contains elements. The unused space starts at sgtable->sgl + sgtable->nents not directly at sgtable->nents and the temporary buffer is placed at the end of this unused space. A subsequent commit will add kunit test cases that demonstrate that the patch is necessary. Pointed out by sashiko.dev on a previous iteration of this series. Link: https://lkml.kernel.org/r/20260326214905.818170-3-lk@c--e.de Fixes: 018584697533 ("netfs: Add a function to extract an iterator into a scatterlist") Signed-off-by: Christian A. Ehrhardt Cc: David Howells Cc: David Gow Cc: Kees Cook Cc: Petr Mladek Cc: [v6.5+] Signed-off-by: Andrew Morton --- lib/scatterlist.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/lib/scatterlist.c b/lib/scatterlist.c index befdc4b9c11d..b7fe91ef35b8 100644 --- a/lib/scatterlist.c +++ b/lib/scatterlist.c @@ -1123,8 +1123,7 @@ static ssize_t extract_user_to_sg(struct iov_iter *iter, size_t len, off; /* We decant the page list into the tail of the scatterlist */ - pages = (void *)sgtable->sgl + - array_size(sg_max, sizeof(struct scatterlist)); + pages = (void *)sg + array_size(sg_max, sizeof(struct scatterlist)); pages -= sg_max; do {