99c07327ae
netlink_dump() is allocating an skb, reserves space in it but forgets to reset network header. This allows a BPF program, invoked later from sk_filter() to access uninitialized kernel memory from the reserved space. Theorically mac header reset could be omitted, because it is set to a special initial value. bpf_internal_load_pointer_neg_helper calls skb_mac_header() without checking skb_mac_header_was_set(). Relying on skb->len not being too big seems fragile. We also could add a sanity check in bpf_internal_load_pointer_neg_helper() to avoid surprises in the future. syzbot report was: BUG: KMSAN: uninit-value in ___bpf_prog_run+0xa22b/0xb420 kernel/bpf/core.c:1637 ___bpf_prog_run+0xa22b/0xb420 kernel/bpf/core.c:1637 __bpf_prog_run32+0x121/0x180 kernel/bpf/core.c:1796 bpf_dispatcher_nop_func include/linux/bpf.h:784 [inline] __bpf_prog_run include/linux/filter.h:626 [inline] bpf_prog_run include/linux/filter.h:633 [inline] __bpf_prog_run_save_cb+0x168/0x580 include/linux/filter.h:756 bpf_prog_run_save_cb include/linux/filter.h:770 [inline] sk_filter_trim_cap+0x3bc/0x8c0 net/core/filter.c:150 sk_filter include/linux/filter.h:905 [inline] netlink_dump+0xe0c/0x16c0 net/netlink/af_netlink.c:2276 netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002 sock_recvmsg_nosec net/socket.c:948 [inline] sock_recvmsg net/socket.c:966 [inline] sock_read_iter+0x5a9/0x630 net/socket.c:1039 do_iter_readv_writev+0xa7f/0xc70 do_iter_read+0x52c/0x14c0 fs/read_write.c:786 vfs_readv fs/read_write.c:906 [inline] do_readv+0x432/0x800 fs/read_write.c:943 __do_sys_readv fs/read_write.c:1034 [inline] __se_sys_readv fs/read_write.c:1031 [inline] __x64_sys_readv+0xe5/0x120 fs/read_write.c:1031 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81 entry_SYSCALL_64_after_hwframe+0x44/0xae Uninit was stored to memory at: ___bpf_prog_run+0x96c/0xb420 kernel/bpf/core.c:1558 __bpf_prog_run32+0x121/0x180 kernel/bpf/core.c:1796 bpf_dispatcher_nop_func include/linux/bpf.h:784 [inline] __bpf_prog_run include/linux/filter.h:626 [inline] bpf_prog_run include/linux/filter.h:633 [inline] __bpf_prog_run_save_cb+0x168/0x580 include/linux/filter.h:756 bpf_prog_run_save_cb include/linux/filter.h:770 [inline] sk_filter_trim_cap+0x3bc/0x8c0 net/core/filter.c:150 sk_filter include/linux/filter.h:905 [inline] netlink_dump+0xe0c/0x16c0 net/netlink/af_netlink.c:2276 netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002 sock_recvmsg_nosec net/socket.c:948 [inline] sock_recvmsg net/socket.c:966 [inline] sock_read_iter+0x5a9/0x630 net/socket.c:1039 do_iter_readv_writev+0xa7f/0xc70 do_iter_read+0x52c/0x14c0 fs/read_write.c:786 vfs_readv fs/read_write.c:906 [inline] do_readv+0x432/0x800 fs/read_write.c:943 __do_sys_readv fs/read_write.c:1034 [inline] __se_sys_readv fs/read_write.c:1031 [inline] __x64_sys_readv+0xe5/0x120 fs/read_write.c:1031 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81 entry_SYSCALL_64_after_hwframe+0x44/0xae Uninit was created at: slab_post_alloc_hook mm/slab.h:737 [inline] slab_alloc_node mm/slub.c:3244 [inline] __kmalloc_node_track_caller+0xde3/0x14f0 mm/slub.c:4972 kmalloc_reserve net/core/skbuff.c:354 [inline] __alloc_skb+0x545/0xf90 net/core/skbuff.c:426 alloc_skb include/linux/skbuff.h:1158 [inline] netlink_dump+0x30f/0x16c0 net/netlink/af_netlink.c:2242 netlink_recvmsg+0x1129/0x1c80 net/netlink/af_netlink.c:2002 sock_recvmsg_nosec net/socket.c:948 [inline] sock_recvmsg net/socket.c:966 [inline] sock_read_iter+0x5a9/0x630 net/socket.c:1039 do_iter_readv_writev+0xa7f/0xc70 do_iter_read+0x52c/0x14c0 fs/read_write.c:786 vfs_readv fs/read_write.c:906 [inline] do_readv+0x432/0x800 fs/read_write.c:943 __do_sys_readv fs/read_write.c:1034 [inline] __se_sys_readv fs/read_write.c:1031 [inline] __x64_sys_readv+0xe5/0x120 fs/read_write.c:1031 do_syscall_x64 arch/x86/entry/common.c:51 [inline] do_syscall_64+0x54/0xd0 arch/x86/entry/common.c:81 entry_SYSCALL_64_after_hwframe+0x44/0xae CPU: 0 PID: 3470 Comm: syz-executor751 Not tainted 5.17.0-syzkaller #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Fixes: db65a3aaf29e ("netlink: Trim skb to alloc size to avoid MSG_TRUNC") Fixes: 9063e21fb026 ("netlink: autosize skb lengthes") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: syzbot <syzkaller@googlegroups.com> Link: https://lore.kernel.org/r/20220415181442.551228-1-eric.dumazet@gmail.com Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.