CVE-2026-89533

In the Linux kernel, the following vulnerability has been resolved:

svcrdma: Fix offset arithmetic in readchunkrange

svcrdmareadchunkrange() 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:

    pclforeach_segment(segment, chunk) {

            if (offset > segment->rs_length) {

                    offset -= segment->rs_length;

                    continue;

            }

            dummy.rshandle = segment->rshandle;

            dummy.rslength = mint(u32, length,

                                    segment->rs_length) - offset;

            dummy.rsoffset = segment->rsoffset + 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.rslength is mint(u32, length, rs_length) -

rslength, which underflows to a near-UINTMAX 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 rslength - offset, not rslength, 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 nrbvec into svcrdmabuildread_segment() and a multi-MiB

kmallocarraynode() in svcrdmagetrwctxt().

Additionally, svcrdmareadcallchunk() 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 svcrdmabuildreadsegment().

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.