46 lines
1.7 KiB
Diff
46 lines
1.7 KiB
Diff
From 0d2b6c2e60fe044c9fb9b9314cc9ede3ead106e7 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 15:50:50 -0700
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Subject: [PATCH] fusermount: bail out on transient config read failure
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If an attacker wishes to use the default configuration instead of the
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system's actual configuration, they can attempt to trigger a failure in
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read_conf(). This only permits increasing mount_max if it is lower than the
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default, so it's not particularly interesting. Still, this should probably
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be prevented robustly; bail out if funny stuff happens when we're trying to
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read the config.
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Note that the classic attack trick of opening so many files that the
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system-wide limit is reached won't work here - because fusermount only
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drops the fsuid, not the euid, the process is running with euid=0 and
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CAP_SYS_ADMIN, so it bypasses the number-of-globally-open-files check in
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get_empty_filp() (unless you're inside a user namespace).
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---
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util/fusermount.c | 9 +++++++++
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1 file changed, 9 insertions(+)
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diff --git a/util/fusermount.c b/util/fusermount.c
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index 143bd4ac..4e0f51a3 100644
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--- a/util/fusermount.c
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+++ b/util/fusermount.c
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@@ -565,10 +565,19 @@ static void read_conf(void)
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fprintf(stderr, "%s: reading %s: missing newline at end of file\n", progname, FUSE_CONF);
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}
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+ if (ferror(fp)) {
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+ fprintf(stderr, "%s: reading %s: read failed\n", progname, FUSE_CONF);
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+ exit(1);
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+ }
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fclose(fp);
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} else if (errno != ENOENT) {
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+ bool fatal = (errno != EACCES && errno != ELOOP &&
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+ errno != ENAMETOOLONG && errno != ENOTDIR &&
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+ errno != EOVERFLOW);
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fprintf(stderr, "%s: failed to open %s: %s\n",
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progname, FUSE_CONF, strerror(errno));
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+ if (fatal)
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+ exit(1);
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}
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}
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