The patch titled Subject: relayfs: fix out-of-bounds access in relay_file_read has been added to the -mm mm-hotfixes-unstable branch. Its filename is relayfs-fix-out-of-bounds-access-in-relay_file_read.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Zhang Zhengming zhang.zhengming@h3c.com Subject: relayfs: fix out-of-bounds access in relay_file_read Date: Wed, 19 Apr 2023 12:02:03 +0800

There is a crash in relay_file_read, as the var from point to the end of last subbuf.

The oops looks something like: pc : __arch_copy_to_user+0x180/0x310 lr : relay_file_read+0x20c/0x2c8 Call trace: __arch_copy_to_user+0x180/0x310 full_proxy_read+0x68/0x98 vfs_read+0xb0/0x1d0 ksys_read+0x6c/0xf0 __arm64_sys_read+0x20/0x28 el0_svc_common.constprop.3+0x84/0x108 do_el0_svc+0x74/0x90 el0_svc+0x1c/0x28 el0_sync_handler+0x88/0xb0 el0_sync+0x148/0x180

We get the condition by analyzing the vmcore:

1). The last produced byte and last consumed byte both at the end of the last subbuf

2). A softirq calls function(e.g __blk_add_trace) to write relay buffer occurs when an program is calling relay_file_read_avail().

relay_file_read relay_file_read_avail relay_file_read_consume(buf, 0, 0); //interrupted by softirq who will write subbuf .... return 1; //read_start point to the end of the last subbuf read_start = relay_file_read_start_pos //avail is equal to subsize avail = relay_file_read_subbuf_avail //from points to an invalid memory address from = buf->start + read_start //system is crashed copy_to_user(buffer, from, avail)

Link: https://lkml.kernel.org/r/20230419040203.37676-1-zhang.zhengming@h3c.com Fixes: 341a7213e5c1 ("kernel/relay.c: fix read_pos error when multiple readers") Signed-off-by: Zhang Zhengming zhang.zhengming@h3c.com Reviewed-by: Zhao Lei zhao_lei1@hoperun.com Reviewed-by: Zhou Kete zhou.kete@h3c.com Cc: Pengcheng Yang yangpc@wangsu.com Cc: Jens Axboe axboe@kernel.dk Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

kernel/relay.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/kernel/relay.c~relayfs-fix-out-of-bounds-access-in-relay_file_read +++ a/kernel/relay.c @@ -989,7 +989,8 @@ static size_t relay_file_read_start_pos( size_t subbuf_size = buf->chan->subbuf_size; size_t n_subbufs = buf->chan->n_subbufs; size_t consumed = buf->subbufs_consumed % n_subbufs; - size_t read_pos = consumed * subbuf_size + buf->bytes_consumed; + size_t read_pos = (consumed * subbuf_size + buf->bytes_consumed) + % (n_subbufs * subbuf_size);

read_subbuf = read_pos / subbuf_size; padding = buf->padding[read_subbuf]; _

Patches currently in -mm which might be from zhang.zhengming@h3c.com are

relayfs-fix-out-of-bounds-access-in-relay_file_read.patch