5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chris Mason <redacted>
commit 4a44c140cc2f3643a39e258bb0c0ab9d0f494f5e upstream.
svc_rdma_read_chunk_range() walks a Read chunk's segment list to
build a sub-range starting at byte offset and spanning length bytes
for a Position-Zero or Call chunk. Two arithmetic defects in the
per-segment loop produce wrong DMA lengths and a u32 underflow:
pcl_for_each_segment(segment, chunk) {
if (offset > segment->rs_length) {
offset -= segment->rs_length;
continue;
}
dummy.rs_handle = segment->rs_handle;
dummy.rs_length = min_t(u32, length,
segment->rs_length) - offset;
dummy.rs_offset = segment->rs_offset + offset;
First, the skip predicate uses '>' instead of '>='. When offset
equals the segment's full rs_length, the segment is fully consumed
and should be skipped, but the loop falls through into the body.
The resulting dummy.rs_length is min_t(u32, length, rs_length) -
rs_length, which underflows to a near-UINT_MAX u32 when length is
smaller than rs_length, or is zero otherwise.
Second, the length formula subtracts offset from the min_t() result
rather than from segment->rs_length before the cap. For offset > 0
the segment's residual is rs_length - offset, not rs_length, so the
cap must be applied to the residual. With the current bracketing,
whenever length is smaller than rs_length - offset the per-segment
length becomes length - offset instead of length, silently dropping
offset bytes from the rebuilt chunk. Combined with the boundary
case above it also enables the u32 underflow path, which propagates
a huge nr_bvec into svc_rdma_build_read_segment() and a multi-MiB
kmalloc_array_node() in svc_rdma_get_rw_ctxt().
Additionally, svc_rdma_read_call_chunk() can invoke this function
with length == 0 when the last Read chunk ends exactly at the end
of the Call chunk. With the corrected >= predicate, every segment
is skipped and the function returns the initial -EINVAL, rejecting
a valid request. Return success immediately when length is zero.
Also break out of the loop once length is fully consumed to avoid
passing zero-length segments to svc_rdma_build_read_segment().
Fix by using '>=' so a fully-consumed segment is skipped, by
moving '- offset' inside min_t() so the cap is applied to the
segment's residual length, by returning success for zero-length
requests, and by stopping iteration when the requested range has
been consumed.
Fixes: d7cc73972661 ("svcrdma: support multiple Read chunks per RPC")
Cc: <redacted>
Assisted-by: kres (claude-opus-4-7)
Signed-off-by: Chris Mason <redacted>
Acked-by: Jeff Layton <jlayton@kernel.org>
Link: https://patch.msgid.link/20260526-rpc-kernel-bugs-v1-2-e251306ccca9@oracle.com (local)
Signed-off-by: Chuck Lever <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/sunrpc/xprtrdma/svc_rdma_rw.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
+++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
@@ -955,17 +955,20 @@ static int svc_rdma_read_chunk_range(str
const struct svc_rdma_segment *segment;
int ret;
+ if (!length)
+ return 0;
+
ret = -EINVAL;
pcl_for_each_segment(segment, chunk) {
struct svc_rdma_segment dummy;
- if (offset > segment->rs_length) {
+ if (offset >= segment->rs_length) {
offset -= segment->rs_length;
continue;
}
dummy.rs_handle = segment->rs_handle;
- dummy.rs_length = min_t(u32, length, segment->rs_length) - offset;
+ dummy.rs_length = min_t(u32, length, segment->rs_length - offset);
dummy.rs_offset = segment->rs_offset + offset;
ret = svc_rdma_build_read_segment(info, &dummy);@@ -974,6 +977,8 @@ static int svc_rdma_read_chunk_range(str
info->ri_totalbytes += dummy.rs_length;
length -= dummy.rs_length;
+ if (!length)
+ break;
offset = 0;
}
return ret;