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tls: cap the output scatter list to something reasonable

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TLS recvmsg() passes user pages as destination for decrypt.
The decrypt operation is repeated record by record, each
record being 16kB, max. TLS allocates an sg_table and uses
iov_iter_get_pages() to populate it with enough pages to
fit the decrypted record.

Even though we decrypt a single message at a time we size
the sg_table based on the entire length of the iovec.
This leads to unnecessarily large allocations, risking
triggering OOM conditions.

Use iov_iter_truncate() / iov_iter_reexpand() to construct
a "capped" version of iov_iter_npages(). Alternatively we
could parametrize iov_iter_npages() to take the size as
arg instead of using i->count, or do something else..

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Jakub Kicinski 2022-02-02 14:20:31 -08:00 committed by David S. Miller
parent 6ff6064605
commit b93235e689
2 changed files with 19 additions and 1 deletions
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17
include/linux/uio.h
View file

@ -273,6 +273,23 @@ static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
i->count = count;
}
static inline int
iov_iter_npages_cap(struct iov_iter *i, int maxpages, size_t max_bytes)
{
size_t shorted = 0;
int npages;
if (iov_iter_count(i) > max_bytes) {
shorted = iov_iter_count(i) - max_bytes;
iov_iter_truncate(i, max_bytes);
}
npages = iov_iter_npages(i, INT_MAX);
if (shorted)
iov_iter_reexpand(i, iov_iter_count(i) + shorted);
return npages;
}
struct csum_state {
__wsum csum;
size_t off;

3
net/tls/tls_sw.c
View file

@ -1433,7 +1433,8 @@ static int decrypt_internal(struct sock *sk, struct sk_buff *skb,
if (*zc && (out_iov || out_sg)) {
if (out_iov)
n_sgout = iov_iter_npages(out_iov, INT_MAX) + 1;
n_sgout = 1 +
iov_iter_npages_cap(out_iov, INT_MAX, data_len);
else
n_sgout = sg_nents(out_sg);
n_sgin = skb_nsg(skb, rxm->offset + prot->prepend_size,