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io_uring/rsrc: fix folio size overflow in io_vec_fill_bvec()

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io_vec_fill_bvec() computes the folio size with a plain int 1:

	unsigned long folio_size = 1 << imu->folio_shift;

imu->folio_shift is unsigned int and comes from folio_shift() of the
folio backing the registered buffer, so it can be 32 or more on a 64 bit
kernel. Shifting int 1 that far is undefined, and on x86 and arm64 the
count is taken modulo 32, so a shift of 34 yields 4 rather than 16G.
Every other folio_shift shift in this file already uses 1UL.

The result is that the segment estimate and the fill loop disagree.
io_estimate_bvec_size() sizes the bvec array with the real shift:

	max_segs += (iov[i].iov_len >> shift) + 2;

so a 1M iovec on a 16G folio is charged 2 segments, while
io_vec_fill_bvec() then walks the same iovec in folio_size chunks of 4
bytes and writes res_bvec[bvec_idx] a quarter of a million times, past
the end of the array it was given. src_bvec is advanced once per
iteration as well, so imu->bvec is read past its end at the same time.
validate_fixed_range() only checks that the range is inside the
registered buffer and does not bound the segment count.

Reaching it needs a folio with a shift of at least 32, which means a
gigantic hugetlb page: 16G on arm64 with 64K pages, where
CONT_PMD_SHIFT is 34 and hugetlb_add_hstate(CONT_PMD_SHIFT - PAGE_SHIFT)
registers that size, and likewise on powerpc. x86_64 tops out at 1G, so
a shift of 30, which still fits in int and is unaffected.

Use 1UL, as the rest of the file does.

Fixes: 9ef4cbbcb4 ("io_uring: add infra for importing vectored reg buffers")
Cc: stable@vger.kernel.org
Signed-off-by: Ali Ahmet Memis <ali@iusegentoo.com>
Link: https://patch.msgid.link/20260802163030.51005-1-ali@iusegentoo.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ali Ahmet Memis 2026-08-02 16:30:30 +00:00 committed by Jens Axboe
parent bb34ae5da3
commit 3f3a6a16bb
1 changed files with 1 additions and 1 deletions
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2
io_uring/rsrc.c
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@ -1477,7 +1477,7 @@ static int io_vec_fill_bvec(int ddir, struct iov_iter *iter,
struct iovec *iovec, unsigned nr_iovs,
struct iou_vec *vec)
{
unsigned long folio_size = 1 << imu->folio_shift;
unsigned long folio_size = 1UL << imu->folio_shift;
unsigned long folio_mask = folio_size - 1;
struct bio_vec *res_bvec = vec->bvec;
size_t total_len = 0;