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    Subject[PATCH 5.0 017/246] sysctl: handle overflow for file-max
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    5.0-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    [ 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 d80bee8ff12e..28ec71d914c7 100644
    --- a/kernel/sysctl.c
    +++ b/kernel/sysctl.c
    @@ -127,6 +127,7 @@ 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;
    static int one_thousand = 1000;
    #ifdef CONFIG_PRINTK
    @@ -1722,6 +1723,8 @@ 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",
    --
    2.19.1


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