bpf: Skip unsettled links in link iterator

bpf_link_prime() inserts a link into link_idr before anon_inode_getfile()
succeeds and before bpf_link_settle() publishes the ID in link->id.
bpf_link_by_id() treats such an ID-zero link as unsettled, but the link
iterator takes a reference without this check.

If anon_inode_getfile() then fails, the creator removes the ID and frees
its still-private link directly.  The iterator is left with a dangling
reference and its next bpf_link_put() accesses freed memory.

Treat ID-zero entries as transient in bpf_link_get_curr_or_next(), just as
bpf_link_by_id() does.

  BUG: KASAN: slab-use-after-free in bpf_link_put
  Write of size 8 by task exp/384
  Call Trace:
  bpf_link_put                    kernel/bpf/syscall.c:3372
  bpf_link_seq_next               kernel/bpf/link_iter.c:33
  bpf_seq_read                    kernel/bpf/bpf_iter.c:158
  vfs_read                        fs/read_write.c:572
  ksys_read                       fs/read_write.c:716
  do_syscall_64                   arch/x86/entry/syscall_64.c:84
  entry_SYSCALL_64_after_hwframe  arch/x86/entry/entry_64.S:121
  Kernel panic - not syncing: KASAN: panic_on_warn set ...

Fixes: 9f8836127308 ("bpf: Add bpf_link iterator")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20260914170206.170723-2-bestswngs@gmail.com

0 files changed, 0 insertions, 0 deletions