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io_uring/epoll: disallow adding an epoll file to an epoll context

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One of the nastier things about epoll is how it allows adding epoll
files to epoll contexts. This leads to all sorts of loop detection
code, and has been a source of issues in the past.

Arguably adding IORING_EPOLL_CTL is a historical mistake on the
io_uring side, but we're kind of stuck with it now as it does seem
to be in use according to code searches. But we can at least minimize
the damage a bit and just disallow this part of epoll, where nesting
issues can arise.

Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe
2026-04-23 05:10:45 -06:00
parent 071858de47
commit cfa1539b24
1 changed files with 3 additions and 0 deletions
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3
io_uring/epoll.c
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@@ -62,6 +62,9 @@ int io_epoll_ctl(struct io_kiocb *req, unsigned int issue_flags)
CLASS(fd, tf)(ie->fd);
if (fd_empty(tf))
return -EBADF;
/* disallow adding an epoll context to another epoll context */
if (ie->op == EPOLL_CTL_ADD && is_file_epoll(fd_file(tf)))
return -EINVAL;
key.file = fd_file(tf);
key.fd = ie->fd;