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author | Stefan Hajnoczi <stefanha@redhat.com> | 2020-05-01 15:06:44 +0100 |
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committer | Dr. David Alan Gilbert <dgilbert@redhat.com> | 2020-05-01 18:41:56 +0100 |
commit | 8c1d353d107b4fc344e27f2f08ea7fa25de2eea2 (patch) | |
tree | bb20ce88beefdd687a4c4eac62820dbaafe8c1d6 /tools | |
parent | 6dbb716877728ce4eb51619885ef6ef4ada9565f (diff) | |
download | qemu-8c1d353d107b4fc344e27f2f08ea7fa25de2eea2.zip qemu-8c1d353d107b4fc344e27f2f08ea7fa25de2eea2.tar.gz qemu-8c1d353d107b4fc344e27f2f08ea7fa25de2eea2.tar.bz2 |
virtiofsd: stay below fs.file-max sysctl value (CVE-2020-10717)
The system-wide fs.file-max sysctl value determines how many files can
be open. It defaults to a value calculated based on the machine's RAM
size. Previously virtiofsd would try to set RLIMIT_NOFILE to 1,000,000
and this allowed the FUSE client to exhaust the number of open files
system-wide on Linux hosts with less than 10 GB of RAM!
Take fs.file-max into account when choosing the default RLIMIT_NOFILE
value.
Fixes: CVE-2020-10717
Reported-by: Yuval Avrahami <yavrahami@paloaltonetworks.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20200501140644.220940-3-stefanha@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r-- | tools/virtiofsd/helper.c | 26 |
1 files changed, 25 insertions, 1 deletions
diff --git a/tools/virtiofsd/helper.c b/tools/virtiofsd/helper.c index dc59f38..00a1ef6 100644 --- a/tools/virtiofsd/helper.c +++ b/tools/virtiofsd/helper.c @@ -176,7 +176,8 @@ void fuse_cmdline_help(void) " default: no_xattr\n" " --rlimit-nofile=<num> set maximum number of file descriptors\n" " (0 leaves rlimit unchanged)\n" - " default: 1,000,000 if the current rlimit is lower\n" + " default: min(1000000, fs.file-max - 16384)\n" + " if the current rlimit is lower\n" ); } @@ -199,9 +200,32 @@ static int fuse_helper_opt_proc(void *data, const char *arg, int key, static unsigned long get_default_rlimit_nofile(void) { + g_autofree gchar *file_max_str = NULL; + const rlim_t reserved_fds = 16384; /* leave at least this many fds free */ rlim_t max_fds = 1000000; /* our default RLIMIT_NOFILE target */ + rlim_t file_max; struct rlimit rlim; + /* + * Reduce max_fds below the system-wide maximum, if necessary. This + * ensures there are fds available for other processes so we don't + * cause resource exhaustion. + */ + if (!g_file_get_contents("/proc/sys/fs/file-max", &file_max_str, + NULL, NULL)) { + fuse_log(FUSE_LOG_ERR, "can't read /proc/sys/fs/file-max\n"); + exit(1); + } + file_max = g_ascii_strtoull(file_max_str, NULL, 10); + if (file_max < 2 * reserved_fds) { + fuse_log(FUSE_LOG_ERR, + "The fs.file-max sysctl is too low (%lu) to allow a " + "reasonable number of open files.\n", + (unsigned long)file_max); + exit(1); + } + max_fds = MIN(file_max - reserved_fds, max_fds); + if (getrlimit(RLIMIT_NOFILE, &rlim) < 0) { fuse_log(FUSE_LOG_ERR, "getrlimit(RLIMIT_NOFILE): %m\n"); exit(1); |