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iov_iter: Fix iov_iter_extract_pages() with zero-sized entries

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iov_iter_extract_pages() doesn't correctly handle skipping over initial
zero-length entries in ITER_KVEC and ITER_BVEC-type iterators.

The problem is that it accidentally reduces maxsize to 0 when it
skipping and thus runs to the end of the array and returns 0.

Fix this by sticking the calculated size-to-copy in a new variable
rather than back in maxsize.

Fixes: 7d58fe7310 ("iov_iter: Add a function to extract a page list from an iterator")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: David Hildenbrand <david@redhat.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Howells 2023-09-08 17:03:20 +01:00 committed by Linus Torvalds
parent 6b8bb5b8d9
commit f741bd7178
1 changed files with 15 additions and 15 deletions
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30
lib/iov_iter.c
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@ -1654,14 +1654,14 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
size_t *offset0)
{
struct page **p, *page;
size_t skip = i->iov_offset, offset;
size_t skip = i->iov_offset, offset, size;
int k;
for (;;) {
if (i->nr_segs == 0)
return 0;
maxsize = min(maxsize, i->bvec->bv_len - skip);
if (maxsize)
size = min(maxsize, i->bvec->bv_len - skip);
if (size)
break;
i->iov_offset = 0;
i->nr_segs--;
@ -1674,16 +1674,16 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
offset = skip % PAGE_SIZE;
*offset0 = offset;
maxpages = want_pages_array(pages, maxsize, offset, maxpages);
maxpages = want_pages_array(pages, size, offset, maxpages);
if (!maxpages)
return -ENOMEM;
p = *pages;
for (k = 0; k < maxpages; k++)
p[k] = page + k;
maxsize = min_t(size_t, maxsize, maxpages * PAGE_SIZE - offset);
iov_iter_advance(i, maxsize);
return maxsize;
size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
iov_iter_advance(i, size);
return size;
}
/*
@ -1698,14 +1698,14 @@ static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
{
struct page **p, *page;
const void *kaddr;
size_t skip = i->iov_offset, offset, len;
size_t skip = i->iov_offset, offset, len, size;
int k;
for (;;) {
if (i->nr_segs == 0)
return 0;
maxsize = min(maxsize, i->kvec->iov_len - skip);
if (maxsize)
size = min(maxsize, i->kvec->iov_len - skip);
if (size)
break;
i->iov_offset = 0;
i->nr_segs--;
@ -1717,13 +1717,13 @@ static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
offset = (unsigned long)kaddr & ~PAGE_MASK;
*offset0 = offset;
maxpages = want_pages_array(pages, maxsize, offset, maxpages);
maxpages = want_pages_array(pages, size, offset, maxpages);
if (!maxpages)
return -ENOMEM;
p = *pages;
kaddr -= offset;
len = offset + maxsize;
len = offset + size;
for (k = 0; k < maxpages; k++) {
size_t seg = min_t(size_t, len, PAGE_SIZE);
@ -1737,9 +1737,9 @@ static ssize_t iov_iter_extract_kvec_pages(struct iov_iter *i,
kaddr += PAGE_SIZE;
}
maxsize = min_t(size_t, maxsize, maxpages * PAGE_SIZE - offset);
iov_iter_advance(i, maxsize);
return maxsize;
size = min_t(size_t, size, maxpages * PAGE_SIZE - offset);
iov_iter_advance(i, size);
return size;
}
/*