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0c0c20aa AM |
1 | From a4e1b7755ebbdee2689d40683ba69f09e38a8d7f Mon Sep 17 00:00:00 2001 |
2 | From: Qualys Security Advisory <qsa@qualys.com> | |
3 | Date: Sun, 21 Feb 2021 22:30:03 -0800 | |
4 | Subject: [PATCH 21/29] Security: Avoid modification of constant data in dkim | |
5 | handling | |
6 | ||
7 | Based on Heiko Schlittermann's commits f880c7f3 and c118c7f4. This | |
8 | fixes: | |
9 | ||
10 | 6/ In src/pdkim/pdkim.c, pdkim_update_ctx_bodyhash() is sometimes called | |
11 | with a global orig_data and hence canon_data, and the following line can | |
12 | therefore modify data that should be constant: | |
13 | ||
14 | 773 canon_data->len = b->bodylength - b->signed_body_bytes; | |
15 | ||
16 | For example, the following proof of concept sets lineending.len to 0 | |
17 | (this should not be possible): | |
18 | ||
19 | (sleep 10; echo 'EHLO test'; sleep 3; echo 'MAIL FROM:<>'; sleep 3; echo 'RCPT TO:postmaster'; sleep 3; echo 'DATA'; date >&2; sleep 30; printf 'DKIM-Signature:a=rsa-sha1;c=simple/simple;l=0\r\n\r\n\r\nXXX\r\n.\r\n'; sleep 30) | nc -n -v 192.168.56.102 25 | |
20 | ||
21 | (gdb) print lineending | |
22 | $1 = {data = 0x55e18035b2ad "\r\n", len = 2} | |
23 | (gdb) print &lineending.len | |
24 | $3 = (size_t *) 0x55e180385948 <lineending+8> | |
25 | (gdb) watch *(size_t *) 0x55e180385948 | |
26 | ||
27 | Hardware watchpoint 1: *(size_t *) 0x55e180385948 | |
28 | Old value = 2 | |
29 | New value = 0 | |
30 | (gdb) print lineending | |
31 | $5 = {data = 0x55e18035b2ad "\r\n", len = 0} | |
32 | --- | |
33 | src/pdkim/pdkim.c | 21 ++++++++++++--------- | |
34 | 1 file changed, 12 insertions(+), 9 deletions(-) | |
35 | ||
36 | diff --git a/src/pdkim/pdkim.c b/src/pdkim/pdkim.c | |
37 | index e3233e9f0..512a3e352 100644 | |
38 | --- a/src/pdkim/pdkim.c | |
39 | +++ b/src/pdkim/pdkim.c | |
40 | @@ -107,7 +107,7 @@ pdkim_combined_canon_entry pdkim_combined_canons[] = { | |
41 | }; | |
42 | ||
43 | ||
44 | -static blob lineending = {.data = US"\r\n", .len = 2}; | |
45 | +static const blob lineending = {.data = US"\r\n", .len = 2}; | |
46 | ||
47 | /* -------------------------------------------------------------------------- */ | |
48 | uschar * | |
49 | @@ -719,9 +719,11 @@ return NULL; | |
50 | If we have to relax the data for this sig, return our copy of it. */ | |
51 | ||
52 | static blob * | |
53 | -pdkim_update_ctx_bodyhash(pdkim_bodyhash * b, blob * orig_data, blob * relaxed_data) | |
54 | +pdkim_update_ctx_bodyhash(pdkim_bodyhash * b, const blob * orig_data, blob * relaxed_data) | |
55 | { | |
56 | -blob * canon_data = orig_data; | |
57 | +const blob * canon_data = orig_data; | |
58 | +size_t left; | |
59 | + | |
60 | /* Defaults to simple canon (no further treatment necessary) */ | |
61 | ||
62 | if (b->canon_method == PDKIM_CANON_RELAXED) | |
63 | @@ -767,16 +769,17 @@ if (b->canon_method == PDKIM_CANON_RELAXED) | |
64 | } | |
65 | ||
66 | /* Make sure we don't exceed the to-be-signed body length */ | |
67 | +left = canon_data->len; | |
68 | if ( b->bodylength >= 0 | |
69 | - && b->signed_body_bytes + (unsigned long)canon_data->len > b->bodylength | |
70 | + && left > (unsigned long)b->bodylength - b->signed_body_bytes | |
71 | ) | |
72 | - canon_data->len = b->bodylength - b->signed_body_bytes; | |
73 | + left = (unsigned long)b->bodylength - b->signed_body_bytes; | |
74 | ||
75 | -if (canon_data->len > 0) | |
76 | +if (left > 0) | |
77 | { | |
78 | - exim_sha_update(&b->body_hash_ctx, CUS canon_data->data, canon_data->len); | |
79 | - b->signed_body_bytes += canon_data->len; | |
80 | - DEBUG(D_acl) pdkim_quoteprint(canon_data->data, canon_data->len); | |
81 | + exim_sha_update(&b->body_hash_ctx, CUS canon_data->data, left); | |
82 | + b->signed_body_bytes += left; | |
83 | + DEBUG(D_acl) pdkim_quoteprint(canon_data->data, left); | |
84 | } | |
85 | ||
86 | return relaxed_data; | |
87 | -- | |
88 | 2.30.2 | |
89 |