From: Christian Brauner christian@brauner.io
[ Upstream commit 32a5ad9c22852e6bd9e74bdec5934ef9d1480bc5 ]
Currently, when writing
echo 18446744073709551616 > /proc/sys/fs/file-max
/proc/sys/fs/file-max will overflow and be set to 0. That quickly crashes the system.
This commit sets the max and min value for file-max. The max value is set to long int. Any higher value cannot currently be used as the percpu counters are long ints and not unsigned integers.
Note that the file-max value is ultimately parsed via __do_proc_doulongvec_minmax(). This function does not report error when min or max are exceeded. Which means if a value largen that long int is written userspace will not receive an error instead the old value will be kept. There is an argument to be made that this should be changed and __do_proc_doulongvec_minmax() should return an error when a dedicated min or max value are exceeded. However this has the potential to break userspace so let's defer this to an RFC patch.
Link: http://lkml.kernel.org/r/20190107222700.15954-3-christian@brauner.io Signed-off-by: Christian Brauner christian@brauner.io Acked-by: Kees Cook keescook@chromium.org Cc: Alexey Dobriyan adobriyan@gmail.com Cc: Al Viro viro@zeniv.linux.org.uk Cc: Dominik Brodowski linux@dominikbrodowski.net Cc: "Eric W. Biederman" ebiederm@xmission.com Cc: Joe Lawrence joe.lawrence@redhat.com Cc: Luis Chamberlain mcgrof@kernel.org Cc: Waiman Long longman@redhat.com [christian@brauner.io: v4] Link: http://lkml.kernel.org/r/20190210203943.8227-3-christian@brauner.io Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/sysctl.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 27f8aa765493..a68fed9f6922 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -125,6 +125,7 @@ static int __maybe_unused one = 1; static int __maybe_unused two = 2; static int __maybe_unused four = 4; static unsigned long one_ul = 1; +static unsigned long long_max = LONG_MAX; static int one_hundred = 100; #ifdef CONFIG_PRINTK static int ten_thousand = 10000; @@ -1521,6 +1522,8 @@ static struct ctl_table fs_table[] = { .maxlen = sizeof(files_stat.max_files), .mode = 0644, .proc_handler = proc_doulongvec_minmax, + .extra1 = &zero, + .extra2 = &long_max, }, { .procname = "nr_open",