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Jagadeesh Krishnanjanappa
be79b8b111
* CVE-2018-10906-1:
fusermount: don't feed "escaped commas" into mount options
The old code permits the following behavior:
$ _FUSE_COMMFD=10000 priv_strace -etrace=mount -s200 fusermount -o 'foobar=\,allow_other' mount
mount("/dev/fuse", ".", "fuse", MS_NOSUID|MS_NODEV, "foobar=\\,allow_other,fd=3,rootmode=40000,user_id=1000,group_id=1000") = -1 EINVAL (Invalid argument)
However, backslashes do not have any special meaning for the kernel here.
As it happens, you can't abuse this because there is no FUSE mount option
that takes a string value that can contain backslashes; but this is very
brittle. Don't interpret "escape characters" in places where they don't
work.
* CVE-2018-10906-2:
fusermount: refuse unknown options
Blacklists are notoriously fragile; especially if the kernel wishes to add
some security-critical mount option at a later date, all existing systems
with older versions of fusermount installed will suddenly have a security
problem.
Additionally, if the kernel's option parsing became a tiny bit laxer, the
blacklist could probably be bypassed.
Whitelist known-harmless flags instead, even if it's slightly more
inconvenient.
Affects fuse < 2.9.8 and fuse < 3.2.5
Signed-off-by: Jagadeesh Krishnanjanappa <jkrishnanjanappa@mvista.com>
Signed-off-by: Armin Kuster <akuster808@gmail.com>
53 lines
1.8 KiB
Diff
53 lines
1.8 KiB
Diff
From 28bdae3d113ef479c1660a581ef720cdc33bf466 Mon Sep 17 00:00:00 2001
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From: Jann Horn <jannh@google.com>
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Date: Fri, 13 Jul 2018 15:15:36 -0700
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Subject: [PATCH] fusermount: don't feed "escaped commas" into mount options
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The old code permits the following behavior:
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$ _FUSE_COMMFD=10000 priv_strace -etrace=mount -s200 fusermount -o 'foobar=\,allow_other' mount
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mount("/dev/fuse", ".", "fuse", MS_NOSUID|MS_NODEV, "foobar=\\,allow_other,fd=3,rootmode=40000,user_id=1000,group_id=1000") = -1 EINVAL (Invalid argument)
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However, backslashes do not have any special meaning for the kernel here.
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As it happens, you can't abuse this because there is no FUSE mount option
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that takes a string value that can contain backslashes; but this is very
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brittle. Don't interpret "escape characters" in places where they don't
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work.
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CVE: CVE-2018-10906
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Upstream-Status: Backport [https://github.com/libfuse/libfuse/commit/28bdae3d113ef479c1660a581ef720cdc33bf466]
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Signed-off-by: Jagadeesh Krishnanjanappa <jkrishnanjanappa@mvista.com>
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---
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util/fusermount.c | 5 ++++-
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1 file changed, 4 insertions(+), 1 deletion(-)
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diff --git a/util/fusermount.c b/util/fusermount.c
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index 0e1d34d..143bd4a 100644
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--- a/util/fusermount.c
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+++ b/util/fusermount.c
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@@ -29,6 +29,7 @@
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#include <sys/socket.h>
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#include <sys/utsname.h>
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#include <sched.h>
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+#include <stdbool.h>
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#define FUSE_COMMFD_ENV "_FUSE_COMMFD"
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@@ -754,8 +755,10 @@ static int do_mount(const char *mnt, char **typep, mode_t rootmode,
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unsigned len;
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const char *fsname_str = "fsname=";
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const char *subtype_str = "subtype=";
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+ bool escape_ok = begins_with(s, fsname_str) ||
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+ begins_with(s, subtype_str);
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for (len = 0; s[len]; len++) {
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- if (s[len] == '\\' && s[len + 1])
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+ if (escape_ok && s[len] == '\\' && s[len + 1])
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len++;
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else if (s[len] == ',')
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break;
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--
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2.13.3
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