bpf: tcp: fix double sock release on batch realloc

bpf_iter_tcp_batch() releases the current batch via
bpf_iter_tcp_put_batch(), which drops the socket refs and rewrites
each slot with the socket cookie, then grows the batch. cur_sk/end_sk
are kept for bpf_iter_tcp_resume(), but on realloc failure the function
returns ERR_PTR() before resume runs, leaving cur_sk < end_sk over
slots that now hold cookies rather than sock pointers.
bpf_iter_tcp_seq_stop() then calls bpf_iter_tcp_put_batch() again and
dereferences a cookie as a struct sock.

Empty the batch on the failure path so stop() does not release it
again. The sockets were already freed by the first
bpf_iter_tcp_put_batch(), so nothing leaks, and a later read() rescans
the bucket from the start instead of skipping it. The sibling
GFP_NOWAIT failure path still holds real socket references and is left
for stop() to release.

  BUG: KASAN: null-ptr-deref in __sock_gen_cookie
  Read of size 8 at addr 0000000000000059 by task exploit
   ...
   __sock_gen_cookie (net/core/sock_diag.c:28)
   bpf_iter_tcp_put_batch (net/ipv4/tcp_ipv4.c:2918)
   bpf_iter_tcp_seq_stop (net/ipv4/tcp_ipv4.c:3270)
   bpf_seq_read (kernel/bpf/bpf_iter.c:205)
   vfs_read (fs/read_write.c:572)
   ksys_read (fs/read_write.c:716)
   do_syscall_64
   entry_SYSCALL_64_after_hwframe
  Kernel panic - not syncing: Fatal exception

Fixes: cdec67a489d4 ("bpf: tcp: Make sure iter->batch always contains a full bucket snapshot")
Reported-by: AutonomousCodeSecurity@microsoft.com
Signed-off-by: Xiang Mei (Microsoft) <xmei5@asu.edu>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Jordan Rife <jordan@jrife.io>
Link: https://patch.msgid.link/20260713233230.3553593-1-xmei5@asu.edu
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index aada52769057731c15aa760b5a3232a01c1b5cbc..b8887cdd66c57184c9badbe2d14212b8c6ddf66f 100644 (file)
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -3146,8 +3146,11 @@ static struct sock *bpf_iter_tcp_batch(struct seq_file *seq)
        bpf_iter_tcp_put_batch(iter);
        err = bpf_iter_tcp_realloc_batch(iter, expected * 3 / 2,
                                         GFP_USER);
-       if (err)
+       if (err) {
+               iter->cur_sk = 0;
+               iter->end_sk = 0;
                return ERR_PTR(err);
+       }
 
        sk = bpf_iter_tcp_resume(seq);
        if (!sk)