From 138c67677ff5ac0bce7131033c39d52a81e87a60 Mon Sep 17 00:00:00 2001 From: Andrii Nakryiko Date: Fri, 1 May 2020 11:56:22 -0700 Subject: [PATCH] bpf: Fix use-after-free of bpf_link when priming half-fails If bpf_link_prime() succeeds to allocate new anon file, but then fails to allocate ID for it, link priming is considered to be failed and user is supposed ot be able to directly kfree() bpf_link, because it was never exposed to user-space. But at that point file already keeps a pointer to bpf_link and will eventually call bpf_link_release(), so if bpf_link was kfree()'d by caller, that would lead to use-after-free. Fix this by first allocating ID and only then allocating file. Adding ID to link_idr is ok, because link at that point still doesn't have its ID set, so no user-space process can create a new FD for it. Fixes: a3b80e107894 ("bpf: Allocate ID for bpf_link") Reported-by: syzbot+39b64425f91b5aab714d@syzkaller.appspotmail.com Suggested-by: Martin KaFai Lau Signed-off-by: Andrii Nakryiko Signed-off-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Link: https://lore.kernel.org/bpf/20200501185622.3088964-1-andriin@fb.com --- kernel/bpf/syscall.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c index 4f34eec..bb1ab7d 100644 --- a/kernel/bpf/syscall.c +++ b/kernel/bpf/syscall.c @@ -2348,19 +2348,20 @@ int bpf_link_prime(struct bpf_link *link, struct bpf_link_primer *primer) if (fd < 0) return fd; - file = anon_inode_getfile("bpf_link", &bpf_link_fops, link, O_CLOEXEC); - if (IS_ERR(file)) { - put_unused_fd(fd); - return PTR_ERR(file); - } id = bpf_link_alloc_id(link); if (id < 0) { put_unused_fd(fd); - fput(file); return id; } + file = anon_inode_getfile("bpf_link", &bpf_link_fops, link, O_CLOEXEC); + if (IS_ERR(file)) { + bpf_link_free_id(id); + put_unused_fd(fd); + return PTR_ERR(file); + } + primer->link = link; primer->file = file; primer->fd = fd; -- 2.7.4