On Thu, 07 Nov 2013 12:14:17 +0800 Jeff Liu <[email protected]> wrote:
> Hi Stephan, > > As per your previous comments for this fix, you have promised another > approach which > is promising to avoid entropy starvation, I got this info from the following > thread: > [PATCH] avoid entropy starvation due to stack protection > https://lkml.org/lkml/2012/12/14/267 > > My current fix has been merged into Andrew's tree(marked in "stuck" state) > for a long > time, and it also works well in our internal specific kernel, I'd like to > know if there > is any update from you, so that we can move it along for mainline. :) This: From: Jeff Liu <[email protected]> Subject: binfmt_elf.c: use get_random_int() to fix entropy depleting Entropy is quickly depleted under normal operations like ls(1), cat(1), etc... between 2.6.30 to current mainline, for instance: $ cat /proc/sys/kernel/random/entropy_avail 3428 $ cat /proc/sys/kernel/random/entropy_avail 2911 $cat /proc/sys/kernel/random/entropy_avail 2620 We observed this problem has been occurring since 2.6.30 with fs/binfmt_elf.c: create_elf_tables()->get_random_bytes(), introduced by f06295b44c296c8f ("ELF: implement AT_RANDOM for glibc PRNG seeding"). /* * Generate 16 random bytes for userspace PRNG seeding. */ get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes)); The patch introduces a wrapper around get_random_int() which has lower overhead than calling get_random_bytes() directly. With this patch applied: $ cat /proc/sys/kernel/random/entropy_avail 2731 $ cat /proc/sys/kernel/random/entropy_avail 2802 $ cat /proc/sys/kernel/random/entropy_avail 2878 Analyzed by John Sobecki. This has been applied on a specific Oracle kernel and has been running on the customer's production environment (the original bug reporter) for several months; it has worked fine until now. Signed-off-by: Jie Liu <[email protected]> Cc: Al Viro <[email protected]> Cc: Andreas Dilger <[email protected]> Cc: Alan Cox <[email protected]> Cc: Arnd Bergmann <[email protected]> Cc: John Sobecki <[email protected]> Cc: James Morris <[email protected]> Cc: Jakub Jelinek <[email protected]> Cc: Ted Ts'o <[email protected]> Cc: Greg Kroah-Hartman <[email protected]> Acked-by: Kees Cook <[email protected]> Cc: Ulrich Drepper <[email protected]> Signed-off-by: Andrew Morton <[email protected]> --- fs/binfmt_elf.c | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff -puN fs/binfmt_elf.c~binfmt_elfc-use-get_random_int-to-fix-entropy-depleting fs/binfmt_elf.c --- a/fs/binfmt_elf.c~binfmt_elfc-use-get_random_int-to-fix-entropy-depleting +++ a/fs/binfmt_elf.c @@ -140,6 +140,25 @@ static int padzero(unsigned long elf_bss #define ELF_BASE_PLATFORM NULL #endif +/* + * Use get_random_int() to implement AT_RANDOM while avoiding depletion + * of the entropy pool. + */ +static void get_atrandom_bytes(unsigned char *buf, size_t nbytes) +{ + unsigned char *p = buf; + + while (nbytes) { + unsigned int random_variable; + size_t chunk = min(nbytes, sizeof(random_variable)); + + random_variable = get_random_int(); + memcpy(p, &random_variable, chunk); + p += chunk; + nbytes -= chunk; + } +} + static int create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec, unsigned long load_addr, unsigned long interp_load_addr) @@ -201,7 +220,7 @@ create_elf_tables(struct linux_binprm *b /* * Generate 16 random bytes for userspace PRNG seeding. */ - get_random_bytes(k_rand_bytes, sizeof(k_rand_bytes)); + get_atrandom_bytes(k_rand_bytes, sizeof(k_rand_bytes)); u_rand_bytes = (elf_addr_t __user *) STACK_ALLOC(p, sizeof(k_rand_bytes)); if (__copy_to_user(u_rand_bytes, k_rand_bytes, sizeof(k_rand_bytes))) _ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
