[PATCH v3] verifiers: fix double close on pgp's sig file descriptor

[Michael Chang]

An error emerged as when I was tesing the verifiers branch, so instead
of putting it in pgp prefix, the verifiers is used to reflect what the
patch is based on.

While running verify_detached, grub aborts with error.

verify_detached /@/.snapshots/1/snapshot/boot/grub/grub.cfg
/@/.snapshots/1/snapshot/boot/grub/grub.cfg.sig

alloc magic is broken at 0x7beea660: 0
Aborted. Press any key to exit.

The error is caused by sig file desciptor been closed twice, first time
in grub_verify_signature() to which it is passed as parameter. Second in
grub_cmd_verify_signature() or in whichever opens the sig file
decriptor. The second close is not consider as bug to me either, as in
common rule of what opens a file has to close it to avoid file
descriptor leakage.

Afterall the design of grub_verify_signature() makes it diffcult to keep
a good trace on opened file descriptor from it's caller. Let's refine
the application interface to accept file path rather than descriptor, in
this way the caller doesn't have to care about closing the descriptor by
delegating it to grub_verify_signature() with full tracing to opened
file descriptor by itself.

Also making it clear that sig descriptor is not referenced in error
returning path of grub_verify_signature_init(), so it can be closed
directly by it's caller. This also makes delegating it to
grub_pubkey_close() infeasible to help in relieving file descriptor
leakage as it has to depend on uncertainty of ctxt fields in error
returning path.

Signed-off-by: Michael Chang <address@hidden>

v1 -> v2:

  - drop change in grub_verify_signature_init()

v2 -> v3

  - Making it clear that sig descriptor is not referenced in error
returning path of grub_verify_signature_init()
---
 grub-core/commands/pgp.c | 35 +++++++++++++++++------------------
 include/grub/pubkey.h    |  2 +-
 2 files changed, 18 insertions(+), 19 deletions(-)

diff --git a/grub-core/commands/pgp.c b/grub-core/commands/pgp.c
index 29e74a640..0487479af 100644
--- a/grub-core/commands/pgp.c
+++ b/grub-core/commands/pgp.c
@@ -495,13 +495,12 @@ grub_verify_signature_init (struct grub_pubkey_context 
*ctxt, grub_file_t sig)
 
   grub_dprintf ("crypt", "alive\n");
 
-  ctxt->sig = sig;
-
   ctxt->hash_context = grub_zalloc (ctxt->hash->contextsize);
   if (!ctxt->hash_context)
     return grub_errno;
 
   ctxt->hash->init (ctxt->hash_context);
+  ctxt->sig = sig;
 
   return GRUB_ERR_NONE;
 }
@@ -684,16 +683,26 @@ grub_pubkey_close (void *ctxt)
 }
 
 grub_err_t
-grub_verify_signature (grub_file_t f, grub_file_t sig,
+grub_verify_signature (grub_file_t f, const char *fsig,
                       struct grub_public_key *pkey)
 {
+  grub_file_t sig;
   grub_err_t err;
   struct grub_pubkey_context ctxt;
   grub_uint8_t *readbuf = NULL;
 
+  sig = grub_file_open (fsig,
+                       GRUB_FILE_TYPE_SIGNATURE
+                       | GRUB_FILE_TYPE_NO_DECOMPRESS);
+  if (!sig)
+    return grub_errno;
+
   err = grub_verify_signature_init (&ctxt, sig);
   if (err)
-    return err;
+    {
+      grub_file_close (sig);
+      return err;
+    }
 
   readbuf = grub_zalloc (READBUF_SIZE);
   if (!readbuf)
@@ -807,7 +816,7 @@ static grub_err_t
 grub_cmd_verify_signature (grub_extcmd_context_t ctxt,
                           int argc, char **args)
 {
-  grub_file_t f = NULL, sig = NULL;
+  grub_file_t f = NULL;
   grub_err_t err = GRUB_ERR_NONE;
   struct grub_public_key *pk = NULL;
 
@@ -845,19 +854,8 @@ grub_cmd_verify_signature (grub_extcmd_context_t ctxt,
       goto fail;
     }
 
-  sig = grub_file_open (args[1],
-                       GRUB_FILE_TYPE_SIGNATURE
-                       | GRUB_FILE_TYPE_NO_DECOMPRESS);
-  if (!sig)
-    {
-      err = grub_errno;
-      goto fail;
-    }
-
-  err = grub_verify_signature (f, sig, pk);
+  err = grub_verify_signature (f, args[1], pk);
  fail:
-  if (sig)
-    grub_file_close (sig);
   if (f)
     grub_file_close (f);
   if (pk)
@@ -902,7 +900,8 @@ grub_pubkey_init (grub_file_t io, enum grub_file_type type 
__attribute__ ((unuse
   err = grub_verify_signature_init (ctxt, sig);
   if (err)
     {
-      grub_pubkey_close (ctxt);
+      grub_free (ctxt);
+      grub_file_close (sig);
       return err;
     }
   *context = ctxt;
diff --git a/include/grub/pubkey.h b/include/grub/pubkey.h
index 4a9d04b43..fb8be9cbb 100644
--- a/include/grub/pubkey.h
+++ b/include/grub/pubkey.h
@@ -25,7 +25,7 @@ struct grub_public_key *
 grub_load_public_key (grub_file_t f);
 
 grub_err_t
-grub_verify_signature (grub_file_t f, grub_file_t sig,
+grub_verify_signature (grub_file_t f, const char *fsig,
                       struct grub_public_key *pk);
 
 
-- 
2.19.1