From: David Howells dhowells@redhat.com
[ Upstream commit 880a88f318cf1d2a0f4c0a7ff7b07e2062b434a4 ]
If an AF_RXRPC service socket is opened and bound, but calls are preallocated, then rxrpc_alloc_incoming_call() will oops because the rxrpc_backlog struct doesn't get allocated until the first preallocation is made.
Fix this by returning NULL from rxrpc_alloc_incoming_call() if there is no backlog struct. This will cause the incoming call to be aborted.
Reported-by: Junvyyang, Tencent Zhuque Lab zhuque@tencent.com Suggested-by: Junvyyang, Tencent Zhuque Lab zhuque@tencent.com Signed-off-by: David Howells dhowells@redhat.com cc: LePremierHomme kwqcheii@proton.me cc: Marc Dionne marc.dionne@auristor.com cc: Willy Tarreau w@1wt.eu cc: Simon Horman horms@kernel.org cc: linux-afs@lists.infradead.org Link: https://patch.msgid.link/20250708211506.2699012-3-dhowells@redhat.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org ---
LLM Generated explanations, may be completely bogus:
**YES**
This commit should be backported to stable kernel trees for the following reasons:
1. **Fixes a Critical Kernel Oops**: The commit addresses a NULL pointer dereference that causes a kernel crash when `rx->backlog` is NULL. At line 257 of the original code, `smp_load_acquire(&b->call_backlog_head)` would dereference a NULL pointer if no preallocation was done.
2. **Minimal and Safe Fix**: The fix is a simple defensive check: ```c + if (!b) + return NULL; ``` This is placed immediately after obtaining the backlog pointer and before any usage. The fix has zero risk of regression - if `b` is NULL, the code would have crashed anyway.
3. **Clear Reproducible Scenario**: The bug occurs in a specific but realistic scenario - when an AF_RXRPC service socket is opened and bound but no calls are preallocated (meaning `rxrpc_service_prealloc()` was never called to allocate the backlog structure).
4. **Follows Stable Kernel Rules**: This fix meets all criteria for stable backporting: - Fixes a real bug that users can hit - Small and contained change (2 lines) - Obviously correct with no side effects - Already tested and merged upstream
5. **Similar to Previously Backported Fixes**: Looking at Similar Commit #2 which was marked YES, it also fixed an oops in the rxrpc preallocation/backlog system with minimal changes.
The commit prevents a kernel crash with a trivial NULL check, making it an ideal candidate for stable backporting.
net/rxrpc/call_accept.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/net/rxrpc/call_accept.c b/net/rxrpc/call_accept.c index 0f5a1d77b890f..94e663a8d323d 100644 --- a/net/rxrpc/call_accept.c +++ b/net/rxrpc/call_accept.c @@ -253,6 +253,9 @@ static struct rxrpc_call *rxrpc_alloc_incoming_call(struct rxrpc_sock *rx, unsigned short call_tail, conn_tail, peer_tail; unsigned short call_count, conn_count;
+ if (!b) + return NULL; + /* #calls >= #conns >= #peers must hold true. */ call_head = smp_load_acquire(&b->call_backlog_head); call_tail = b->call_backlog_tail;