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epoll: Keep a reference on files added to the check list

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commit a9ed4a6560b8562b7e2e2bed9527e88001f7b682 upstream.

When adding a new fd to an epoll, and that this new fd is an
epoll fd itself, we recursively scan the fds attached to it
to detect cycles, and add non-epool files to a "check list"
that gets subsequently parsed.

However, this check list isn't completely safe when deletions
can happen concurrently. To sidestep the issue, make sure that
a struct file placed on the check list sees its f_count increased,
ensuring that a concurrent deletion won't result in the file
disapearing from under our feet.

Cc: stable@vger.kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Change-Id: I780923748a8387fa6b3174b952ca22994a377170
CVE-2020-0466
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>
This commit is contained in:
Marc Zyngier
2021-01-03 21:26:48 +01:00
committed by Francescodario Cuzzocrea
parent 06a7012a02
commit d6e07ffd39
1 changed files with 7 additions and 2 deletions
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fs/eventpoll.c
+7 -2
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@@ -1591,9 +1591,11 @@ static int ep_loop_check_proc(void *priv, void *cookie, int call_nests)
* not already there, and calling reverse_path_check()
* during ep_insert().
*/
if (list_empty(&epi->ffd.file->f_tfile_llink))
if (list_empty(&epi->ffd.file->f_tfile_llink)) {
get_file(epi->ffd.file);
list_add(&epi->ffd.file->f_tfile_llink,
&tfile_check_list);
}
}
}
mutex_unlock(&ep->mtx);
@@ -1637,6 +1639,7 @@ static void clear_tfile_check_list(void)
file = list_first_entry(&tfile_check_list, struct file,
f_tfile_llink);
list_del_init(&file->f_tfile_llink);
fput(file);
}
INIT_LIST_HEAD(&tfile_check_list);
}
@@ -1773,8 +1776,10 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
clear_tfile_check_list();
goto error_tgt_fput;
}
} else
} else {
get_file(tfile);
list_add(&tfile->f_tfile_llink, &tfile_check_list);
}
}
mutex_lock_nested(&ep->mtx, 0);