From: Christian Brauner <christian@xxxxxxxxxx> Subject: sysctl: handle overflow in proc_get_long proc_get_long() is a funny function. It uses simple_strtoul() and for a good reason. proc_get_long() wants to always succeed the parse and return the maybe incorrect value and the trailing characters to check against a pre-defined list of acceptable trailing values. However, simple_strtoul() explicitly ignores overflows which can cause funny things like the following to happen: echo 18446744073709551616 > /proc/sys/fs/file-max cat /proc/sys/fs/file-max 0 (Which will cause your system to silently die behind your back.) On the other hand kstrtoul() does do overflow detection but does not return the trailing characters, and also fails the parse when anything other than '\n' is a trailing character whereas proc_get_long() wants to be more lenient. Now, before adding another kstrtoul() function let's simply add a static parse strtoul_lenient() which: - fails on overflow with -ERANGE - returns the trailing characters to the caller The reason why we should fail on ERANGE is that we already do a partial fail on overflow right now. Namely, when the TMPBUFLEN is exceeded. So we already reject values such as 184467440737095516160 (21 chars) but accept values such as 18446744073709551616 (20 chars) but both are overflows. So we should just always reject 64bit overflows and not special-case this based on the number of chars. Link: http://lkml.kernel.org/r/20190107222700.15954-2-christian@xxxxxxxxxx Signed-off-by: Christian Brauner <christian@xxxxxxxxxx> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx> Cc: "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx> Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx> Cc: Joe Lawrence <joe.lawrence@xxxxxxxxxx> Cc: Waiman Long <longman@xxxxxxxxxx> Cc: Dominik Brodowski <linux@xxxxxxxxxxxxxxxxxxxx> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx> Cc: Alexey Dobriyan <adobriyan@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- --- a/kernel/sysctl.c~sysctl-handle-overflow-in-proc_get_long +++ a/kernel/sysctl.c @@ -67,6 +67,8 @@ #include <linux/bpf.h> #include <linux/mount.h> +#include "../lib/kstrtox.h" + #include <linux/uaccess.h> #include <asm/processor.h> @@ -2117,6 +2119,41 @@ static void proc_skip_char(char **buf, s } } +/** + * strtoul_lenient - parse an ASCII formatted integer from a buffer and only + * fail on overflow + * + * @cp: kernel buffer containing the string to parse + * @endp: pointer to store the trailing characters + * @base: the base to use + * @res: where the parsed integer will be stored + * + * In case of success 0 is returned and @res will contain the parsed integer, + * @endp will hold any trailing characters. + * This function will fail the parse on overflow. If there wasn't an overflow + * the function will defer the decision what characters count as invalid to the + * caller. + */ +static int strtoul_lenient(const char *cp, char **endp, unsigned int base, + unsigned long *res) +{ + unsigned long long result; + unsigned int rv; + + cp = _parse_integer_fixup_radix(cp, &base); + rv = _parse_integer(cp, base, &result); + if ((rv & KSTRTOX_OVERFLOW) || (result != (unsigned long)result)) + return -ERANGE; + + cp += rv; + + if (endp) + *endp = (char *)cp; + + *res = (unsigned long)result; + return 0; +} + #define TMPBUFLEN 22 /** * proc_get_long - reads an ASCII formatted integer from a user buffer @@ -2160,7 +2197,8 @@ static int proc_get_long(char **buf, siz if (!isdigit(*p)) return -EINVAL; - *val = simple_strtoul(p, &p, 0); + if (strtoul_lenient(p, &p, 0, val)) + return -EINVAL; len = p - tmp; _
