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From 520f09be3c2d351722c33daf7389d6ac4716be98 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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---
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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 26a0b75bbecb..5175c0115a05 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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@@ -739,8 +740,10 @@ 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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2.14.3
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