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@ -1,16 +1,32 @@
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commit a3a4d5ea80dc34e7a14952380b85be8b1b0bc1e3
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Author: Damien Goutte-Gattat <dgouttegattat@incenp.org>
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Date: Wed Dec 10 01:24:36 2014 +0100
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From 3e13d5493c74427655a7208a7bc4fcbcabda6774 Mon Sep 17 00:00:00 2001
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From: Damien Goutte-Gattat <dgouttegattat@incenp.org>
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Date: Wed, 28 Jan 2015 16:03:10 +0100
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Subject: [PATCH 2/2] Remove extra nul byte in signature data
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To: gnupg-devel@gnupg.org
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Remove extra nul byte in signature data
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GPG Agent prepends a nul byte in the signature value if the first
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byte has its most signifiant bit set, to prevent it from being
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interpreted as a sign bit. We need to remove that byte when it is
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present.
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* src/agent.c (scute_agent_sign): Check for extra nul byte at the
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beginning of signature data.
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--
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GPG Agent 2.1 prepends a nul byte in the signature value if the first
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byte has its most significant bit set, to prevent it from being
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interpreted as a sign bit (see agent_pksign_do, in GnuPG's
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agent/pksign.c).
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But Scute expects the signature to be always of a fixed size (128 or
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256 bytes), and it will reject a signature containing this extra nul
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byte.
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This patch makes Scute read the effective size of the signature from
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the S-expression, and remove the prepended nul byte if present.
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Signed-off-by: Damien Goutte-Gattat <dgouttegattat@incenp.org>
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---
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src/agent.c | 57 ++++++++++++++++++++++++++++++++-------------------------
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1 file changed, 32 insertions(+), 25 deletions(-)
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diff --git a/src/agent.c b/src/agent.c
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index b1fdbf0..525c2a9 100644
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index 9265ca2..547c587 100644
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--- a/src/agent.c
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+++ b/src/agent.c
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@@ -981,13 +981,12 @@ pksign_cb (void *opaque, const void *buffer, size_t length)
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@ -28,9 +44,9 @@ index b1fdbf0..525c2a9 100644
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+#define SIG_MIN_LEN 128
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+#define SIG_MAX_LEN 256
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static unsigned char sha1_prefix[15] = /* (1.3.14.3.2.26) */
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@@ -1033,14 +1032,14 @@ scute_agent_sign (char *grip, unsigned char *data, int len,
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/* Call the agent to learn about a smartcard. */
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gpg_error_t
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@@ -1009,14 +1008,14 @@ scute_agent_sign (char *grip, unsigned char *data, int len,
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if (sig_result == NULL)
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{
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/* FIXME: We return the largest supported size - is that correct? */
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@ -47,7 +63,7 @@ index b1fdbf0..525c2a9 100644
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return gpg_error (GPG_ERR_INV_ARG);
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snprintf (cmd, sizeof (cmd), "SIGKEY %s", grip);
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@@ -1092,30 +1091,37 @@ scute_agent_sign (char *grip, unsigned char *data, int len,
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@@ -1041,30 +1040,38 @@ scute_agent_sign (char *grip, unsigned char *data, int len,
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return err;
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/* FIXME: we need a real parser to cope with all kind of S-expressions. */
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@ -65,42 +81,46 @@ index b1fdbf0..525c2a9 100644
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- else
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- {
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- if (sig.len != SIG_PREFIX_LEN + SIG_LEN + SIG_POSTFIX_LEN)
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+ int data_len;
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+ unsigned char *sig_begin;
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+ unsigned char *sig_val;
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+ unsigned int sig_val_len;
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+
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+ data_len = atoi(sig.data + SIG_PREFIX_LEN);
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+ sig_begin = strchr(sig.data + SIG_PREFIX_LEN, ':');
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+ if (!sig_begin) /* Invalid S-expression? */
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+ sig_val_len = strtol (sig.data + SIG_PREFIX_LEN, (char **)&sig_val, 10);
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+
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+ if (*(sig_val++) != ':')
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return gpg_error (GPG_ERR_BAD_SIGNATURE);
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- if (memcmp (sig.data, SIG_PREFIX, SIG_PREFIX_LEN))
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+
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+ sig_begin += 1; /* Skip colon. */
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+
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+ if (sig.len != sig_begin - sig.data + data_len + SIG_POSTFIX_LEN)
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+ if (sig.len != sig_val - sig.data + sig_val_len + SIG_POSTFIX_LEN)
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return gpg_error (GPG_ERR_BAD_SIGNATURE);
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- if (memcmp (sig.data + sig.len - SIG_POSTFIX_LEN,
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- SIG_POSTFIX, SIG_POSTFIX_LEN))
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+ if (memcmp (sig.data + sig.len - SIG_POSTFIX_LEN, SIG_POSTFIX, SIG_POSTFIX_LEN))
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+ if (memcmp (sig.data + sig.len - SIG_POSTFIX_LEN, SIG_POSTFIX,
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+ SIG_POSTFIX_LEN))
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return gpg_error (GPG_ERR_BAD_SIGNATURE);
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- memcpy (sig_result, sig.data + SIG_PREFIX_LEN, SIG_LEN);
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- *sig_len = SIG_LEN;
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+
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+ if ( *sig_begin == 0 && *(sig_begin+1) & 0x80 )
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+ if ( *sig_val == 0 && *(sig_val+1) & 0x80 )
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+ {
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+ /* Remove the extra nul byte that was added to prevent
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+ * the signature from being interpreted as a negative value. */
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+ sig_begin += 1;
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+ data_len -= 1;
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+ sig_val += 1;
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+ sig_val_len -= 1;
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+ }
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+
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+ memcpy (sig_result, sig_begin, data_len);
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+ *sig_len = data_len;
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+ if ( sig_val_len > *sig_len )
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+ return gpg_error (GPG_ERR_TOO_LARGE);
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+
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+ memcpy (sig_result, sig_val, sig_val_len);
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+ *sig_len = sig_val_len;
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}
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-
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-
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+ else
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+ return gpg_error( GPG_ERR_BAD_SIGNATURE ); /* Unexpected signature prefix. */
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+ return gpg_error( GPG_ERR_BAD_SIGNATURE ); /* Unexpected prefix. */
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+
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return 0;
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}
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--
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1.8.4
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