From: Eric Dumazet <edumazet@google.com> stable inclusion from stable-v6.6.117 commit ed71f801249d2350c77a73dca2c03918a15a62fe category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/13525 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit 1534ff77757e44bcc4b98d0196bc5c0052fce5fa ] syzbot reported a possible shift-out-of-bounds [1] Blamed commit added rto_alpha_max and rto_beta_max set to 1000. It is unclear if some sctp users are setting very large rto_alpha and/or rto_beta. In order to prevent user regression, perform the test at run time. Also add READ_ONCE() annotations as sysctl values can change under us. [1] UBSAN: shift-out-of-bounds in net/sctp/transport.c:509:41 shift exponent 64 is too large for 32-bit type 'unsigned int' CPU: 0 UID: 0 PID: 16704 Comm: syz.2.2320 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120 ubsan_epilogue lib/ubsan.c:233 [inline] __ubsan_handle_shift_out_of_bounds+0x27f/0x420 lib/ubsan.c:494 sctp_transport_update_rto.cold+0x1c/0x34b net/sctp/transport.c:509 sctp_check_transmitted+0x11c4/0x1c30 net/sctp/outqueue.c:1502 sctp_outq_sack+0x4ef/0x1b20 net/sctp/outqueue.c:1338 sctp_cmd_process_sack net/sctp/sm_sideeffect.c:840 [inline] sctp_cmd_interpreter net/sctp/sm_sideeffect.c:1372 [inline] Fixes: b58537a1f562 ("net: sctp: fix permissions for rto_alpha and rto_beta knobs") Reported-by: syzbot+f8c46c8b2b7f6e076e99@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/690c81ae.050a0220.3d0d33.014e.GAE@google.com/... Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Xin Long <lucien.xin@gmail.com> Link: https://patch.msgid.link/20251106111054.3288127-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com> --- net/sctp/transport.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 31eca29..abb44c0 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -495,6 +495,7 @@ void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt) if (tp->rttvar || tp->srtt) { struct net *net = tp->asoc->base.net; + unsigned int rto_beta, rto_alpha; /* 6.3.1 C3) When a new RTT measurement R' is made, set * RTTVAR <- (1 - RTO.Beta) * RTTVAR + RTO.Beta * |SRTT - R'| * SRTT <- (1 - RTO.Alpha) * SRTT + RTO.Alpha * R' @@ -506,10 +507,14 @@ void sctp_transport_update_rto(struct sctp_transport *tp, __u32 rtt) * For example, assuming the default value of RTO.Alpha of * 1/8, rto_alpha would be expressed as 3. */ - tp->rttvar = tp->rttvar - (tp->rttvar >> net->sctp.rto_beta) - + (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> net->sctp.rto_beta); - tp->srtt = tp->srtt - (tp->srtt >> net->sctp.rto_alpha) - + (rtt >> net->sctp.rto_alpha); + rto_beta = READ_ONCE(net->sctp.rto_beta); + if (rto_beta < 32) + tp->rttvar = tp->rttvar - (tp->rttvar >> rto_beta) + + (((__u32)abs((__s64)tp->srtt - (__s64)rtt)) >> rto_beta); + rto_alpha = READ_ONCE(net->sctp.rto_alpha); + if (rto_alpha < 32) + tp->srtt = tp->srtt - (tp->srtt >> rto_alpha) + + (rtt >> rto_alpha); } else { /* 6.3.1 C2) When the first RTT measurement R is made, set * SRTT <- R, RTTVAR <- R/2. -- 2.9.5