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| author | Eric Dumazet <edumazet@google.com> | 2025-11-06 11:10:54 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-12-03 12:45:17 +0100 |
| commit | 0e0413e3315199b23ff4aec295e256034cd0a6e4 (patch) | |
| tree | cdc6da7481132b752ffa68f9b02a9c4d3096bf73 | |
| parent | 203a0dace3e2221d3cd110491aebe99b02de8bed (diff) | |
| download | linux-stable-0e0413e3315199b23ff4aec295e256034cd0a6e4.tar.gz linux-stable-0e0413e3315199b23ff4aec295e256034cd0a6e4.zip | |
sctp: prevent possible shift-out-of-bounds in sctp_transport_update_rto
[ 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/T/#u
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>
| -rw-r--r-- | net/sctp/transport.c | 13 |
1 files changed, 9 insertions, 4 deletions
diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 9c721d70df9c..992104107978 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -337,6 +337,7 @@ 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' @@ -348,10 +349,14 @@ 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. |