6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Chris Mason <redacted>
commit b7713a784c59515d0aba558c8f5df6a0164dd3a9 upstream.
When a parsed chunk list contains a chunk whose ch_segcount is zero,
pcl_for_each_segment computes its inclusive upper bound as
&chunk->ch_segments[ch_segcount - 1]. ch_segcount is u32, so the
subtraction wraps to 0xFFFFFFFF and the bound lands far past the
ch_segments flex array. The loop body then walks unrelated memory at
sizeof(struct svc_rdma_segment) stride until it faults.
A zero-segcount chunk is reachable from the wire:
xdr_check_write_chunk() only rejects segcount values greater than
rc_maxpages, and pcl_alloc_write() links a freshly allocated chunk
onto rc_write_pcl/rc_reply_pcl before its segment-fill loop runs,
so a Write or Reply chunk advertising zero segments leaves
ch_segcount == 0 on the list. When the transport has negotiated
Send-With-Invalidate, svc_rdma_get_inv_rkey() iterates all four
PCLs with pcl_for_each_segment and dereferences segment->rs_handle
on each iteration, turning the underflow into an out-of-bounds read
and a general protection fault.
xdr_check_write_list / xdr_check_reply_chunk
pcl_alloc_write()
chunk = pcl_alloc_chunk(...) /* ch_segcount = 0 */
list_add_tail(&chunk->ch_list, &pcl->cl_chunks)
/* fill loop iterates zero times for wire segcount 0 */
svc_rdma_get_inv_rkey()
pcl_for_each_chunk(rc_write_pcl)
pcl_for_each_segment(segment, chunk)
pos <= &ch_segments[0u - 1u] /* 0xFFFFFFFF */
segment->rs_handle /* OOB read -> GPF */
Fix by switching the macro to a half-open upper bound that uses
ch_segcount directly. For ch_segcount == 0 the loop start equals the
loop end and the body is skipped; for ch_segcount > 0 the iteration
range is unchanged. All six existing call sites in
net/sunrpc/xprtrdma/svc_rdma_recvfrom.c and
net/sunrpc/xprtrdma/svc_rdma_rw.c remain correct under the new bound,
so no caller changes are needed.
Fixes: 78147ca8b4a9 ("svcrdma: Add a "parsed chunk list" data structure")
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-v1-4-e251306ccca9@oracle.com (local)
Signed-off-by: Chuck Lever <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/sunrpc/svc_rdma_pcl.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/include/linux/sunrpc/svc_rdma_pcl.h
+++ b/include/linux/sunrpc/svc_rdma_pcl.h
@@ -97,7 +97,7 @@ pcl_next_chunk(const struct svc_rdma_pcl
*/
#define pcl_for_each_segment(pos, chunk) \
for (pos = &(chunk)->ch_segments[0]; \
- pos <= &(chunk)->ch_segments[(chunk)->ch_segcount - 1]; \
+ pos < &(chunk)->ch_segments[(chunk)->ch_segcount]; \
pos++)
/**