Patch "bpf: Add extra path pointer check to d_path helper" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    bpf: Add extra path pointer check to d_path helper

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     bpf-add-extra-path-pointer-check-to-d_path-helper.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c142aada3c30babcb00f61ea444b5a72d24b693a
Author: Jiri Olsa <jolsa@xxxxxxxxxx>
Date:   Tue Jun 6 11:17:14 2023 -0700

    bpf: Add extra path pointer check to d_path helper
    
    [ Upstream commit f46fab0e36e611a2389d3843f34658c849b6bd60 ]
    
    Anastasios reported crash on stable 5.15 kernel with following
    BPF attached to lsm hook:
    
      SEC("lsm.s/bprm_creds_for_exec")
      int BPF_PROG(bprm_creds_for_exec, struct linux_binprm *bprm)
      {
              struct path *path = &bprm->executable->f_path;
              char p[128] = { 0 };
    
              bpf_d_path(path, p, 128);
              return 0;
      }
    
    But bprm->executable can be NULL, so bpf_d_path call will crash:
    
      BUG: kernel NULL pointer dereference, address: 0000000000000018
      #PF: supervisor read access in kernel mode
      #PF: error_code(0x0000) - not-present page
      PGD 0 P4D 0
      Oops: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC NOPTI
      ...
      RIP: 0010:d_path+0x22/0x280
      ...
      Call Trace:
       <TASK>
       bpf_d_path+0x21/0x60
       bpf_prog_db9cf176e84498d9_bprm_creds_for_exec+0x94/0x99
       bpf_trampoline_6442506293_0+0x55/0x1000
       bpf_lsm_bprm_creds_for_exec+0x5/0x10
       security_bprm_creds_for_exec+0x29/0x40
       bprm_execve+0x1c1/0x900
       do_execveat_common.isra.0+0x1af/0x260
       __x64_sys_execve+0x32/0x40
    
    It's problem for all stable trees with bpf_d_path helper, which was
    added in 5.9.
    
    This issue is fixed in current bpf code, where we identify and mark
    trusted pointers, so the above code would fail even to load.
    
    For the sake of the stable trees and to workaround potentially broken
    verifier in the future, adding the code that reads the path object from
    the passed pointer and verifies it's valid in kernel space.
    
    Fixes: 6e22ab9da793 ("bpf: Add d_path helper")
    Reported-by: Anastasios Papagiannis <tasos.papagiannnis@xxxxxxxxx>
    Suggested-by: Alexei Starovoitov <ast@xxxxxxxxxx>
    Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
    Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
    Acked-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
    Acked-by: Yonghong Song <yhs@xxxxxx>
    Link: https://lore.kernel.org/bpf/20230606181714.532998-1-jolsa@xxxxxxxxxx
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index b314e71a008ce..8b3531172d8e2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -849,13 +849,23 @@ static const struct bpf_func_proto bpf_send_signal_thread_proto = {
 
 BPF_CALL_3(bpf_d_path, struct path *, path, char *, buf, u32, sz)
 {
+	struct path copy;
 	long len;
 	char *p;
 
 	if (!sz)
 		return 0;
 
-	p = d_path(path, buf, sz);
+	/*
+	 * The path pointer is verified as trusted and safe to use,
+	 * but let's double check it's valid anyway to workaround
+	 * potentially broken verifier.
+	 */
+	len = copy_from_kernel_nofault(&copy, path, sizeof(*path));
+	if (len < 0)
+		return len;
+
+	p = d_path(&copy, buf, sz);
 	if (IS_ERR(p)) {
 		len = PTR_ERR(p);
 	} else {