58 lines
2.1 KiB
Diff
58 lines
2.1 KiB
Diff
From 5a62eb5734d50fe556934aefa3bac5698372f00e Mon Sep 17 00:00:00 2001
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From: Joseph Sutton <josephsutton@catalyst.net.nz>
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Date: Mon, 15 Aug 2022 16:53:45 +1200
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Subject: [PATCH 11/15] CVE-2022-3437 source4/heimdal: Avoid undefined
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behaviour in _gssapi_verify_pad()
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By decrementing 'pad' only when we know it's safe, we ensure we can't
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stray backwards past the start of a buffer, which would be undefined
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behaviour.
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In the previous version of the loop, 'i' is the number of bytes left to
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check, and 'pad' is the current byte we're checking. 'pad' was
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decremented at the end of each loop iteration. If 'i' was 1 (so we
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checked the final byte), 'pad' could potentially be pointing to the
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first byte of the input buffer, and the decrement would put it one
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byte behind the buffer.
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That would be undefined behaviour.
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The patch changes it so that 'pad' is the byte we previously checked,
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which allows us to ensure that we only decrement it when we know we
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have a byte to check.
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BUG: https://bugzilla.samba.org/show_bug.cgi?id=15134
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Signed-off-by: Joseph Sutton <josephsutton@catalyst.net.nz>
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Reviewed-by: Andrew Bartlett <abartlet@samba.org>
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Conflict: NA
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Reference: https://download.samba.org/pub/samba/patches/security/samba-4.15.11-security-2022-10-25.patch
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---
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source4/heimdal/lib/gssapi/krb5/decapsulate.c | 6 +++---
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1 file changed, 3 insertions(+), 3 deletions(-)
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diff --git a/source4/heimdal/lib/gssapi/krb5/decapsulate.c b/source4/heimdal/lib/gssapi/krb5/decapsulate.c
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index 86085f56950..4e3fcd659e9 100644
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--- a/source4/heimdal/lib/gssapi/krb5/decapsulate.c
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+++ b/source4/heimdal/lib/gssapi/krb5/decapsulate.c
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@@ -193,13 +193,13 @@ _gssapi_verify_pad(gss_buffer_t wrapped_token,
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if (wrapped_token->length < 1)
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return GSS_S_BAD_MECH;
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- pad = (u_char *)wrapped_token->value + wrapped_token->length - 1;
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- padlength = *pad;
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+ pad = (u_char *)wrapped_token->value + wrapped_token->length;
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+ padlength = pad[-1];
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if (padlength > datalen)
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return GSS_S_BAD_MECH;
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- for (i = padlength; i > 0 && *pad == padlength; i--, pad--)
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+ for (i = padlength; i > 0 && *--pad == padlength; i--)
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;
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if (i != 0)
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return GSS_S_BAD_MIC;
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--
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2.25.1
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