Re: [PATCH net] sctp: fix memory leak in sctp_stream_outq_migrate()
From: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Date: 2022-11-22 23:35:26
Also in:
linux-sctp
On Fri, Nov 18, 2022 at 10:15:50PM -0500, Xin Long wrote:
On Fri, Nov 18, 2022 at 3:48 AM Zhengchao Shao [off-list ref] wrote:quoted
When sctp_stream_outq_migrate() is called to release stream out resources, the memory pointed to by prio_head in stream out is not released. The memory leak information is as follows: unreferenced object 0xffff88801fe79f80 (size 64): comm "sctp_repo", pid 7957, jiffies 4294951704 (age 36.480s) hex dump (first 32 bytes): 80 9f e7 1f 80 88 ff ff 80 9f e7 1f 80 88 ff ff ................ 90 9f e7 1f 80 88 ff ff 90 9f e7 1f 80 88 ff ff ................ backtrace: [<ffffffff81b215c6>] kmalloc_trace+0x26/0x60 [<ffffffff88ae517c>] sctp_sched_prio_set+0x4cc/0x770 [<ffffffff88ad64f2>] sctp_stream_init_ext+0xd2/0x1b0 [<ffffffff88aa2604>] sctp_sendmsg_to_asoc+0x1614/0x1a30 [<ffffffff88ab7ff1>] sctp_sendmsg+0xda1/0x1ef0 [<ffffffff87f765ed>] inet_sendmsg+0x9d/0xe0 [<ffffffff8754b5b3>] sock_sendmsg+0xd3/0x120 [<ffffffff8755446a>] __sys_sendto+0x23a/0x340 [<ffffffff87554651>] __x64_sys_sendto+0xe1/0x1b0 [<ffffffff89978b49>] do_syscall_64+0x39/0xb0 [<ffffffff89a0008b>] entry_SYSCALL_64_after_hwframe+0x63/0xcd Fixes: 637784ade221 ("sctp: introduce priority based stream scheduler") Reported-by: syzbot+29c402e56c4760763cc0@syzkaller.appspotmail.com Signed-off-by: Zhengchao Shao <redacted> --- net/sctp/stream.c | 6 ++++++ 1 file changed, 6 insertions(+)diff --git a/net/sctp/stream.c b/net/sctp/stream.c index ef9fceadef8d..a17dc368876f 100644 --- a/net/sctp/stream.c +++ b/net/sctp/stream.c@@ -70,6 +70,9 @@ static void sctp_stream_outq_migrate(struct sctp_stream *stream, * sctp_stream_update will swap ->out pointers. */ for (i = 0; i < outcnt; i++) { + if (SCTP_SO(new, i)->ext) + kfree(SCTP_SO(new, i)->ext->prio_head); + kfree(SCTP_SO(new, i)->ext); SCTP_SO(new, i)->ext = SCTP_SO(stream, i)->ext; SCTP_SO(stream, i)->ext = NULL;@@ -77,6 +80,9 @@ static void sctp_stream_outq_migrate(struct sctp_stream *stream, } for (i = outcnt; i < stream->outcnt; i++) { + if (SCTP_SO(stream, i)->ext) + kfree(SCTP_SO(stream, i)->ext->prio_head); + kfree(SCTP_SO(stream, i)->ext); SCTP_SO(stream, i)->ext = NULL; } --2.17.1This is not a proper fix: 1. you shouldn't access "prio_head" outside stream_sched_prio.c. 2. the prio_head you freed might be used by other out streams, freeing it unconditionally would cause either a double free or use after free. I'm afraid we have to add a ".free_sid" in sctp_sched_ops, and implement it for sctp_sched_prio, like: +static void sctp_sched_prio_free_sid(struct sctp_stream *stream, __u16 sid) +{ + struct sctp_stream_priorities *prio = SCTP_SO(stream, sid)->ext->prio_head; + int i; + + if (!prio) + return; + + SCTP_SO(stream, sid)->ext->prio_head = NULL; + for (i = 0; i < stream->outcnt; i++) {
Instead of checking all streams, the for() can/should be replaced by (from sctp_sched_prio_free): if (!list_empty(&prio->prio_sched)) return;
quoted hunk ↗ jump to hunk
+ if (SCTP_SO(stream, i)->ext && + SCTP_SO(stream, i)->ext->prio_head == prio) + return; + } + kfree(prio); +} + static void sctp_sched_prio_free(struct sctp_stream *stream) { struct sctp_stream_priorities *prio, *n;@@ -323,6 +340,7 @@ static struct sctp_sched_ops sctp_sched_prio = { .get = sctp_sched_prio_get, .init = sctp_sched_prio_init, .init_sid = sctp_sched_prio_init_sid, + .free_sid = sctp_sched_prio_free_sid, .free = sctp_sched_prio_free, .enqueue = sctp_sched_prio_enqueue, .dequeue = sctp_sched_prio_dequeue,then call it in sctp_stream_outq_migrate(), like: +static void sctp_stream_free_ext(struct sctp_stream *stream, __u16 sid) +{ + struct sctp_sched_ops *sched = sctp_sched_ops_from_stream(stream); + + sched->free_sid(stream, sid); + kfree(SCTP_SO(stream, sid)->ext); + SCTP_SO(stream, sid)->ext = NULL; +} + /* Migrates chunks from stream queues to new stream queues if needed, * but not across associations. Also, removes those chunks to streams * higher than the new max.@@ -70,16 +79,14 @@ static void sctp_stream_outq_migrate(structsctp_stream *stream, * sctp_stream_update will swap ->out pointers. */ for (i = 0; i < outcnt; i++) { - kfree(SCTP_SO(new, i)->ext); + sctp_stream_free_ext(new, i); SCTP_SO(new, i)->ext = SCTP_SO(stream, i)->ext; SCTP_SO(stream, i)->ext = NULL; } } - for (i = outcnt; i < stream->outcnt; i++) { - kfree(SCTP_SO(stream, i)->ext); - SCTP_SO(stream, i)->ext = NULL; - } + for (i = outcnt; i < stream->outcnt; i++) + sctp_stream_free_ext(new, i); } Marcelo, do you see a better solution?
No. Your suggestion is the best I could think of too. Another approach would be to expose sched->free and do all the freeing at once, like sctp_stream_free() does. But the above is looks cleaner and makes it evident that freeing 'ext' is not trivial. With the proposal above, sctp_sched_prio_free() becomes an optimization, if we can call it that. With the for/if replacement above, not even that, and should be removed. Including sctp_sched_ops 'free' pointer. sctp_stream_free() then should be updated to use the new sctp_stream_free_ext() instead, instead of mangling it directly. Makes sense? Thanks, Marcelo