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authorMarc Zyngier <maz@kernel.org>2020-08-19 17:12:17 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-08-26 10:31:06 +0200
commit4957d56414ff5ca8fe62f8f11f0f9814f35b1d11 (patch)
tree0fc664b8f3c1fe612350c54315eabb246289c1c9
parent2ff3c97b47521d6700cc6485c7935908dcd2c27c (diff)
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epoll: Keep a reference on files added to the check list
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>
-rw-r--r--fs/eventpoll.c9
1 files changed, 7 insertions, 2 deletions
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 58f48ea0db23..d804ad60be73 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -1890,9 +1890,11 @@ 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);
@@ -1936,6 +1938,7 @@ 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);
}
@@ -2095,9 +2098,11 @@ SYSCALL_DEFINE4(epoll_ctl, int, epfd, int, op, int, fd,
clear_tfile_check_list();
goto error_tgt_fput;
}
- } else
+ } else {
+ get_file(tf.file);
list_add(&tf.file->f_tfile_llink,
&tfile_check_list);
+ }
mutex_lock_nested(&ep->mtx, 0);
if (is_file_epoll(tf.file)) {
tep = tf.file->private_data;