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mingw: fix quoting of arguments

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We need to be careful to follow proper quoting rules. For example, if an
argument contains spaces, we have to quote them. Double-quotes need to
be escaped. Backslashes need to be escaped, but only if they are
followed by a double-quote character.

We need to be _extra_ careful to consider the case where an argument
ends in a backslash _and_ needs to be quoted: in this case, we append a
double-quote character, i.e. the backslash now has to be escaped!

The current code, however, fails to recognize that, and therefore can
turn an argument that ends in a single backslash into a quoted argument
that now ends in an escaped double-quote character. This allows
subsequent command-line parameters to be split and part of them being
mistaken for command-line options, e.g. through a maliciously-crafted
submodule URL during a recursive clone.

Technically, we would not need to quote _all_ arguments which end in a
backslash _unless_ the argument needs to be quoted anyway. For example,
`test\` would not need to be quoted, while `test \` would need to be.

To keep the code simple, however, and therefore easier to reason about
and ensure its correctness, we now _always_ quote an argument that ends
in a backslash.

This addresses CVE-2019-1350.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
This commit is contained in:
Johannes Schindelin 2019-09-13 16:32:43 +02:00
parent a8dee3ca61
commit 6d8684161e
2 changed files with 20 additions and 3 deletions
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9
compat/mingw.c
View File

@ -872,7 +872,7 @@ static const char *quote_arg(const char *arg)
p++;
len++;
}
if (*p == '"')
if (*p == '"' || !*p)
n += count*2 + 1;
continue;
}
@ -894,16 +894,19 @@ static const char *quote_arg(const char *arg)
count++;
*d++ = *arg++;
}
if (*arg == '"') {
if (*arg == '"' || !*arg) {
while (count-- > 0)
*d++ = '\\';
/* don't escape the surrounding end quote */
if (!*arg)
break;
*d++ = '\\';
}
}
*d++ = *arg++;
}
*d++ = '"';
*d++ = 0;
*d++ = '\0';
return q;
}

14
t/t7416-submodule-dash-url.sh
View File

@ -31,4 +31,18 @@ test_expect_success 'clone rejects unprotected dash' '
test_i18ngrep ignoring err
'
test_expect_success 'trailing backslash is handled correctly' '
git init testmodule &&
test_commit -C testmodule c &&
git submodule add ./testmodule &&
: ensure that the name ends in a double backslash &&
sed -e "s|\\(submodule \"testmodule\\)\"|\\1\\\\\\\\\"|" \
-e "s|url = .*|url = \" --should-not-be-an-option\"|" \
<.gitmodules >.new &&
mv .new .gitmodules &&
git commit -am "Add testmodule" &&
test_must_fail git clone --verbose --recurse-submodules . dolly 2>err &&
test_i18ngrep ! "unknown option" err
'
test_done