From 2d9396c2feac8b707b367c64cd59604d7bc86a33 Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 14 Dec 2023 16:47:46 -0500 Subject: [PATCH 1/2] t5100: make rfc822 comment test more careful When processing "From" headers in an email, mailinfo "unquotes" quoted strings and rfc822 parenthesized comments. For quoted strings, we actually remove the double-quotes, so: From: "A U Thor" become: Author: A U Thor Email: someone@example.com But for comments, we leave the outer parentheses in place, so: From: A U (this is a comment) Thor becomes: Author: A U (this is a comment) Thor Email: someone@example.com So what is the comment "unquoting" actually doing? In our code, being in a comment section has exactly two effects: 1. We'll unquote backslash-escaped characters inside a comment section. 2. We _won't_ unquote double-quoted strings inside a comment section. Our test for comments in t5100 checks this: From: "A U Thor" (this is \(really\) a comment (honestly)) So it is covering (1), but not (2). Let's add in a quoted string to cover this. Moreover, because the comment appears at the end of the From header, there's nothing to confirm that we correctly found the end of the comment section (and not just the end-of-string). Let's instead move it to the beginning of the header, which means we can confirm that the existing quoted string is detected (which will only happen if we know we've left the comment block). As expected, the test continues to pass, but this will give us more confidence as we refactor the code in the next patch. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- t/t5100/comment.expect | 2 +- t/t5100/comment.in | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-) diff --git a/t/t5100/comment.expect b/t/t5100/comment.expect index 7228177984..bd71956a47 100644 --- a/t/t5100/comment.expect +++ b/t/t5100/comment.expect @@ -1,4 +1,4 @@ -Author: A U Thor (this is (really) a comment (honestly)) +Author: (this is (really) a "comment" (honestly)) A U Thor Email: somebody@example.com Subject: testing comments Date: Sun, 25 May 2008 00:38:18 -0700 diff --git a/t/t5100/comment.in b/t/t5100/comment.in index c53a192dfe..0b7e903b06 100644 --- a/t/t5100/comment.in +++ b/t/t5100/comment.in @@ -1,5 +1,5 @@ From 1234567890123456789012345678901234567890 Mon Sep 17 00:00:00 2001 -From: "A U Thor" (this is \(really\) a comment (honestly)) +From: (this is \(really\) a "comment" (honestly)) "A U Thor" Date: Sun, 25 May 2008 00:38:18 -0700 Subject: [PATCH] testing comments From dee182941fb685f5d85e61a0e9d97e8e91512f6c Mon Sep 17 00:00:00 2001 From: Jeff King Date: Thu, 14 Dec 2023 16:48:59 -0500 Subject: [PATCH 2/2] mailinfo: avoid recursion when unquoting From headers Our unquote_comment() function is recursive; when it sees a comment within a comment, like: (this is an (embedded) comment) it recurses to handle the inner comment. This is fine for practical use, but it does mean that you can easily run out of stack space with a malicious header. For example: perl -e 'print "From: ", "(" x 2**18;' | git mailinfo /dev/null /dev/null segfaults on my system. And since mailinfo is likely to be fed untrusted input from the Internet (if not by human users, who might recognize a garbage header, but certainly there are automated systems that apply patches from a list) it may be possible for an attacker to trigger the problem. That said, I don't think there's an interesting security vulnerability here. All an attacker can do is make it impossible to parse their email and apply their patch, and there are lots of ways to generate bogus emails. So it's more of an annoyance than anything. But it's pretty easy to fix it. The recursion is not helping us preserve any particular state from each level. The only flag in our parsing is take_next_literally, and we can never recurse when it is set (since the start of a new comment implies it was not backslash-escaped). So it is really only useful for finding the end of the matched pair of parentheses. We can do that easily with a simple depth counter. Signed-off-by: Jeff King Signed-off-by: Junio C Hamano --- mailinfo.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mailinfo.c b/mailinfo.c index 542d4458f6..4acf7cb601 100644 --- a/mailinfo.c +++ b/mailinfo.c @@ -57,6 +57,7 @@ static void parse_bogus_from(struct mailinfo *mi, const struct strbuf *line) static const char *unquote_comment(struct strbuf *outbuf, const char *in) { int take_next_literally = 0; + int depth = 1; strbuf_addch(outbuf, '('); @@ -70,11 +71,14 @@ static const char *unquote_comment(struct strbuf *outbuf, const char *in) take_next_literally = 1; continue; case '(': - in = unquote_comment(outbuf, in); + strbuf_addch(outbuf, '('); + depth++; continue; case ')': strbuf_addch(outbuf, ')'); - return in; + if (!--depth) + return in; + continue; } }